Подофілотоксин та арилтетралінові лігнани: методи синтезу кілець A, B, C, D

Podophyllotoxin, its derivatives and structural analogues are an extensive group of aryl-tetralin-lignans of interest in pharmacology due to their promising anticancer and antitumor activity. The synthesis methods that have been proposed to date seek to resolve synthetic, stereochemical, pharmacodyn...

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Опубліковано в:Журнал органічної та фармацевтичної хімії
Дата:2024
Том:22
Випуск:2
Сторінки:3-25
ISSN:2518-1548
Автори та афіліації:
  • Francisco Flores-Hernández — Laboratorio de Química Farmacéutica, Departamento de Farmacobiología, Centro Universitario de Ciencias Exactas e Ingenierías Universidad de Guadalajara
  • Tania Isabel Zárate-López — Laboratorio de Química Farmacéutica, Departamento de Farmacobiología, Centro Universitario de Ciencias Exactas e Ingenierías Universidad de Guadalajara
  • Marco Antonio Alcaráz-Cano — Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos — ORCID: 0000-0003-1754-0751
  • Jaime Escalante — Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos
  • José Domingo Rivera-Ramírez — Laboratorio de Química Farmacéutica, Departamento de Farmacobiología, Centro Universitario de Ciencias Exactas e Ingenierías Universidad de Guadalajara
Автори: Flores-Hernández, Francisco, Zárate-López, Tania Isabel, Alcaráz-Cano, Marco Antonio, Escalante, Jaime, Rivera-Ramírez, José Domingo
Формат: Стаття
Мова:Англійська
Опубліковано: National University of Pharmacy 2024
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Назва журналу:Journal of Organic and Pharmaceutical Chemistry
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Journal of Organic and Pharmaceutical Chemistry
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author Flores-Hernández, Francisco
Zárate-López, Tania Isabel
Alcaráz-Cano, Marco Antonio
Escalante, Jaime
Rivera-Ramírez, José Domingo
author_facet Flores-Hernández, Francisco
Zárate-López, Tania Isabel
Alcaráz-Cano, Marco Antonio
Escalante, Jaime
Rivera-Ramírez, José Domingo
author_institution_txt_mv [ { "author": "Francisco Flores-Hernández", "institution": "Laboratorio de Química Farmacéutica, Departamento de Farmacobiología, Centro Universitario de Ciencias Exactas e Ingenierías Universidad de Guadalajara", "orcid": "" }, { "author": "Tania Isabel Zárate-López", "institution": "Laboratorio de Química Farmacéutica, Departamento de Farmacobiología, Centro Universitario de Ciencias Exactas e Ingenierías Universidad de Guadalajara", "orcid": "" }, { "author": "Marco Antonio Alcaráz-Cano", "institution": "Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos", "orcid": "0000-0003-1754-0751" }, { "author": "Jaime Escalante", "institution": "Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos", "orcid": "" }, { "author": "José Domingo Rivera-Ramírez", "institution": "Laboratorio de Química Farmacéutica, Departamento de Farmacobiología, Centro Universitario de Ciencias Exactas e Ingenierías Universidad de Guadalajara", "orcid": "" } ]
author_orcid_str_mv 0000-0003-1754-0751
author_sort Flores-Hernández, Francisco
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container_title Журнал органічної та фармацевтичної хімії
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description Podophyllotoxin, its derivatives and structural analogues are an extensive group of aryl-tetralin-lignans of interest in pharmacology due to their promising anticancer and antitumor activity. The synthesis methods that have been proposed to date seek to resolve synthetic, stereochemical, pharmacodynamic and environmental aspects. In this review we have updated and brought together different classifications of lignan and podophyllotoxin synthesis. Transformation methods focus on the strategies used to form or functionalize rings A, B, C and D, as well as the configuration of the system of four stereogenic centers that fuse rings C and D.
doi_str_mv 10.24959/ophcj.24.308942
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fulltext ISSN 2308-8303 (Print) / 2518-1548 (Online) 3 Review Article http://ophcj.nuph.edu.ua UDC [547.7+547.6]:54.057 F. Flóres-Hernández1, T. I. Zárate-López1, M. A. Alcaráz-Cano2, J. Escalante2, J. D. Rivera-Ramírez1 1 Laboratorio de Química Farmacéutica, Departamento de Farmacobiología, Centro Universitario de Ciencias Exactas e Ingenierías Universidad de Guadalajara, 1421 Blvd. Gral. Marcelino García Barragán, Olímpica, 44430 Guadalajara, México 2 Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos, 1001 Avenida Universidad, 62209 Cuernavaca, México Podophyllotoxin and Aryltetralin Lignans: Methods for the Synthesis of Rings A, B, C, D Abstract Podophyllotoxin, its derivatives and structural analogs are an extensive group of aryl-tetralin-lignans of interest in pharma- cology due to their promising anticancer and antitumor activity. The synthesis methods proposed to date are aimed at solv- ing synthetic, stereochemical, pharmacodynamic and environmental aspects. In this review, we have updated and brought together different classifications of lignan and podophyllotoxin synthesis. Transformation methods focus on the strategies used to form or functionalize rings A, B, C and D, as well as the configuration of the system of four stereogenic centers that fuse rings C and D. Keywords: lignans; podophyllotoxin; aryltetralin-lignans; etoposide; teniposide Ф. Флорес-Ернандес1, Т. І. Сарате-Лопес1, М. А. Алькарас-Кано2, Х. Ескаланте2, Х. Д. Рівера-Рамірес1 1 Лабораторія фармацевтичної хімії, Департамент фармакобіології, Університетський центр точних наук та техніки, Університет Гвадалахари, бульвар Марселіно Гарсія Барраган, 1421, Олімпіка, м. Гвадалахара, 44430, Халіско, Мексика 2 Центр хімічних досліджень, Автономний університет штату Морелос, Університетський проспект, 1001, Куернавака, 62209, Морелос, Мексика Подофілотоксин та арилтетралінові лігнани: методи синтезу кілець A, B, C, D Анотація Подофілотоксин, його похідні та структурні аналоги є великою групою арилтетралінових лігнанів, що становлять ін- терес для фармакології, зокрема завдяки їхній багатонадійній протипухлинній дії. Методи синтезу, запропоновані сьогодні, спрямовані на вирішення синтетичних, стереохімічних, фармакодинамічних та екологічних аспектів. У цьо- му огляді ми оновили й об’єднали різні класифікації синтезу подофілотоксину та споріднених сполук. Обговорені методи зосереджені на стратегіях формування або функціоналізації кілець A, B, C і D, а також на конфігурації чотирьох стереогенних центрів, які поєднують кільця C і D. Ключові слова: лігнани; подофілотоксин; арилтетралінові лігнани; етопозид; теніпозид Citation: Flóres-Hernández, F.; Zárate-López, T. I.; Alcaráz-Cano, M. A.; Escalante, J.; Rivera-Ramírez, J. D. Podophyllotoxin and aryltetralin lignans: Methods for the synthesis of rings A, B, C, D. Journal of Organic and Pharmaceutical Chemistry 2024, 22 (2), 3 – 25. https://doi.org/10.24959/ophcj.24.308942 Received: 23 July 2024; Revised: 5 September 2024; Accepted: 7 September 2024 Copyright© 2024, F. Flóres-Hernández, T. I. Zárate-López, M. A. Alcaráz-Cano, J. Escalante, J. D. Rivera-Ramírez. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0). Funding: The authors thank the Consejo Nacional de Humanidades Ciencia y Tecnología (CONAHCYT) for the funding granted to carry out this research through the Ciencia Frontera project No. 610262 called “The chemo-enzymatic synthesis of podophyllotoxin-type lignans using green chemistry bases and their evaluation as probable antitumor compounds.” Conflict of interest: The authors have no conflict of interest to declare. ISSN 2308-8303 (Print) / 2518-1548 (Online) 4 Журнал органічної та фармацевтичної хімії 2024, 22 (2) ■ The Structure, Chemical and Pharmacological Properties of Podophyllotoxin Podophyllotoxin (1) is the most prominent and abundant metabolite of the lignan family. It has been isolated from the roots, seeds, fruits and re- sins of plant species of the Berberidaceae family, mainly from the genus Podophyllum and Bursera. The first isolation dates to 1880 when Poewys- sotzky obtained it from podophyllin resin [1, 2]. The description of a podophyllotoxin molecu- le uses structural, steric, and reactive criteria, which serve to determine aspects of transforma- tion and design of the biological activity when de- rivatives and analogs are prepared. Structurally, podophyllotoxin is an aryltetralin lignan. Lignans are a family of secondary metabolites of the shi- kimic acid pathway and can be divided into four groups: lignans, neolignans, oxyneolignans, and lignanoids (trimers and analogs) [3]. Cyclolignans form the σ backbone when two phenylpropanoid units (C6C3) are linked through their respective positions 8, also called β positions (this is a non- IUPAC nomenclature system based on their bio- genesis; 2 and 3, Scheme 1, A). In nature, phenyl- propanoid units are found in the form of propenyl- phenols 4 and cinnamyl alcohols 5 (Scheme 1, B), which, via the enzymatic oxidation, form lignans of type 6 and 7 (Scheme 1, C). The prefix arylte- tralin comes from the fact that podophyllotoxin contains a tetralin unit substituted with an aryl group (8). In the complete molecule of podophyl- lotoxin, it is possible to distinguish its five rings, which nomenclature was proposed by Moss [1]: the first four are fused, dioxolane (A), tetralin (B and C) and β-lactone (D); for its part, ring E (3,4,5-trimethoxyphenyl) is linked to tetralin. From the stereochemical point of view, four con- tiguous stereogenic centers can be distinguished in positions 7 (R), 8 (S), 7’ (R), and 8’ (S), which are denoted as 4, 3, 1, and 2, in accordance with the rules of systematic numbering for 1. In this review, each position will be denoted referring to this last classification. Finally, it is possible to distinguish that the lactone ring (D) is fused to ring C in a relative trans-configuration. From the pharmacological point of view, po- dophyllotoxin has been used for hundreds of years in traditional Chinese, Japanese, and Indian Ayur- vedic medicine due to its antiviral and antitumor properties [2]. It has been used as an antidote against poisoning, as purgative, anthelmintic, and as a poison to treat venereal warts, and it has anti-HIV properties. By 1942, Kaplan reported the best treatment for that time of condylomata acu- minata caused by the human papillomavirus [3]. By 1946, it was found that it could inhibit cell division and destroy rapidly proliferating cells due to its antimitotic and cytotoxic properties. Other reported activities include transcriptase inhibition, cardiovascular effects, immunomo- dulation, antileishmanial activity, high density lipoprotein activity, antifungal, antipsoriasis, antimalarial, antiasthmatic and anti-HIV activi- ty [2]. The mechanism of action of podophyllotoxin is in microtubules. By binding to the colchicine Me MeO O O O O O O OH MeO OMe OMe O 1 7 8 1 2 34 E B DA C 1 2 3 4 5 6 7(α) 8(β) 9(γ) 1' 2' 3' 4' 5' 6' 7'(α') 8'(β') 9'(γ') 8(β) 8'(β') A 2 3 B R2MeO HO R1 4: R1 = H a) R2 = CH2OH b) R2 = CO2H c) R2 = Me R2MeO HO R1 5: R1 = OMe O O H H OH OMe HO MeO 6 5 6 Scheme 1. The structure of podophyllotoxin (1), structural definitions of lignans (2, 3, and 8), and examples of lignans in nature (4, 5, 6, and 7) ISSN 2308-8303 (Print) / 2518-1548 (Online) 5 Journal of Organic and Pharmaceutical Chemistry 2024, 22 (2) site of the beta-tubulin subunit, it prevents it from binding to guanosine triphosphate (GTP). Thus, by interrupting the formation and stabi- lization of the microtubules that make up the cytoskeleton of eukaryotic cells, it interrupts the formation of the mitotic spindle and causes destabilization of the microtubule structure in the G2/M phase (Figure 1) [3, 4]. In addition, podophyllotoxin is highly effec- tive in the treatment of skin diseases, such as genital warts caused by the human papillomavi- rus (HPV), molluscum contagiosum and precan- cerous lesions, as well as it is highly potential as an anticancer agent due to its ability to stop cell division. Its antitumor activity has been pro- ven in the treatment of Wilms tumors, genital tu- mors, non-Hodgkin lymphomas and lung cancer. However, its use for cancer treatment is limited since it is toxic and can cause serious gastroin- testinal side effects, such as irritation, ulceration, pain, inflammation, and burns. For this reason, podophyllotoxin has been used as a precursor to obtain semisynthetic derivatives that are clini- cally applied as cytostatics in the treatment of various types of cancer [5]. Etoposide (9), teniposide (10) and etopofos (11) (Figure 2) are synthetic derivatives of podo- phyllotoxin with efficacy, enhanced selectivity, and low toxicity. They are used in chemotherapy against testicular cancer, lung cancer, and lym- phoma, leukemia, Kaposi’s sarcoma. However, they have such limitations as the development of drug resistance and myelosuppression. These compounds have a structural base of aryltetralin lignans similar to podophyllotoxin. However, the differences are that the configura- tion of position 4 is opposite (S) and the substi- tuent of that position is a protected glycosyl group. Additionally, etopofos contains a phosphate group in position 4’ of ring E [6]. These structural varia- tions generate a mechanism that is now based on the irreveersible inhibition of topoisomerase II, by forming a ternary DNA-topoisomerase-drug complex, which causes the accumulation of DNA- drug complexes. This prevents cell replication and transcription, causing double strand breaks in DNA and leading to apoptosis. Etoposide also shows other biological activities, such as cyto- toxic, insecticidal, antifungal, antiviral, anti- inflammatory, neurotoxic, immunosuppressive, Figure 1. The representation of the position and constitution of microtubules in the eukaryotic cell and of the colchicine site in the β subunit of tubulin O O O MeO OR2 OMe O O Etoposide (9) OO OR1 HO HO R1 = Me S Teniposide (10) R1 = Me Etopofos (11) R2 = H R2 = P OH O OH R2 = H R1 = Figure 2. Chemical structures of etoposide (9), teniposide (10) and etopofos (11) ISSN 2308-8303 (Print) / 2518-1548 (Online) 6 Журнал органічної та фармацевтичної хімії 2024, 22 (2) antirheumatic, antispasmogenic and hypolipide- mic action [5]. These findings demonstrated the therapeutic potential of aryl-tetralin lignans and led to the development of a new class of antineoplastics known as podophyllotoxin analogs and deriva- tives. These compounds are used in combination with other chemotherapeutic agents to improve efficacy and reduce side effects of cancer treat- ments. In some cases, podophyllotoxin deriva- tives have been shown to be effective in treating cancers that are resistant to other chemothera- peutic treatments (Figure 3) [7]. Thus, an extensive multidisciplinary research network has been generated, so the demand for podophyllotoxin and its derivatives continues to increase. The proof of this is the growing number of works and research areas in this field. For the first half of 2023, for example, considering the search engines Google academics and Concordia University Library, the number of publications referring to podophyllotoxin until 2022 (a range of approximately 80 years) was around 4000 pub- lications, approximately 50 publications per year. However, only in the period of 2022 to 2023 (18 months) approximately 700 publications were recorded with podophyllotoxin as a central topic, something like 39 monthly publications, at least one daily! By April 2024, around 500 articles had already been published on this topic, three per day. ■ The Synthesis of Aryltetralin Lignans Type Podophyllotoxin The history of podophyllotoxin synthe- sis methods In this bibliographic review, we will present a general overview of the efforts to obtain podo- phyllotoxin or one of its derivatives. This review of the most used synthesis methods is carried out, considering three aspects: (a) starting ma- terials, (b) strategies to form rings A, B, C or D and (c) strategies for controlling the configura- tion of positions 1, 2, 3 and 4. Our aim is to gen- erate a document that allows us to identify the existing methodologies for constructing strate- gic intermediate positions or structures, as well as the reaction conditions, catalysts, reagents, reaction media and efficient, rapid transforma- tion sequences and economics that made them possible. The race for the synthesis of podophyllotoxin and its derivatives began in the 1950s after a long accumulation of scientific evidence about its bio- logical activity. The first methods for obtaining it used two strategies: the intramolecular Diels- Alder reaction (vide infra) and the epimerization of picropodophyllotoxin by racemization of posi- tion 2 via the formation of enolates. Through this latter methodology, diasteromeric mixtures of 45/55 of podophyllotoxin (1) and picropodophyl- lotoxin (13) were reported, which could be sepa- rated via crystallization with a yield of 38 % of podophyllotoxin (Scheme 2). Years later, San Fe- liciano also used this strategy in the synthesis of podophyllotoxin [8, 9]. The second stage of these studies around the family of molecules began in the 1970s [10] with the first efforts to obtain the glycosylated ana- logs – etoposide [5], teniposide and etopophos [3]. Although the synthesis of these compounds is not related either the neolignan structure or the re- solution of its stereogenic centers, or, on the other hand, their mechanism of action was not related to the synthesis of tubulin, but with topoisome- rase, their notable therapeutic activity gave cer- tainty to the pharmacological potential of their chemical structure and encouraged the search for new lignans. O O Ar1 OMe O O O Ar1 O O OH O O Ar1 O O OH O O Ar1 OH O OH OH O O Ar1 O O O O Ar1 O O O Ar1 O O O O O O Ar1 O O 12 (e )pipodophillotoxin 16 (y )atein 13 (p )icropodphillotoxin 17 (p )odophillic aldehyde 14 (p )odophillic acid 18 ( )(+)-burseran 15 (d )eoxipodophillotoxin 19 ( )�-apopicropodophillotoxin Figure 3. The podophyllotoxin analogs most studied from a pharmacological point of view ISSN 2308-8303 (Print) / 2518-1548 (Online) 7 Journal of Organic and Pharmaceutical Chemistry 2024, 22 (2) The synthesis of rings A and B The third stage was the search for total syn- thesis methods of podophyllotoxin and its ana- logs (Scheme 3). In 1991, Ward provided a va- luable compilation of all the synthesis methods available up to that time and defined a general classification of four methods according to the type of transformation used, which was useful for later classifications. Thus, the methods of (a) oxoester, (b) hydroxyester, (c) Diels-Alder, and (d) conjuga- te addition, could be distinguished. These methods share two characteristics, each one focuses on the specific formation of ring C and, they all started from some derivative of 1,3-benzodioxol (methy- lenedioxyphenyl or piperonyl group). These start- ing materials have predominated in the search 1 O O Ar1 O O OH 13 O O Ar1 O O O O O Ar1 O O OHO Na Scheme 2. Epimerization of picropodophyllotoxin (13), through the protection of the hydroxyl group with a pyranyl group, and sodium enolate formation to obtain podophyllotoxin (1) O O O O OH O O O O O Ar1 O O O OTIPS O O Ar1 O O OH Ar1 O O CO2Me Me Ar1 O CO2Et Me MeO O O OH O O O O OHO Ar3 O O O O Cl O O O OH Br O O O Ar1 O O O MgBr H 26 24 28 27 29 O O OH 21 O O CO2H O Ar1 O O OMe O O O H O Br 22 MeO HO OH 31 O O 30 OH O NH2 O O H O 20 O O SR SR O O O O Ph O O Ar1 CO2Me CO2Me O O Ar2 CO2Et CO2Et O O CN OTBS O O OMe OMe O O O O OH O O O O O I Br O O O CO2Me MeO2C Ar O O O O Br O O N O Br Me Ph Me H O O O O Ar1 CO2Et O 20 O O Ar1 CO2Et CO2H O O O O Ar1 CO2Me CO2Et O O O Ar1 O O O O Ar1 O I, 48, 50, 7c, 52 II, 57 III, 22, 23 IV, 46 V, 61 VI, 64a VII, 18, 24 VIII, 39 IX, 48 X, 32, 33 XI, 25b XII, 25a XIII, 44a, 35b XIV, 67 XV, 68 XVI, 60 XVII, 28, 66 XVIII, 26 XIX, 35a, 35b, 67 XX XXI, 69, 71 XXII, 27 XXIII XXIV, 63 XXV, 62 XXVI XXVII, 10 R2 R1 R3 Ar 1 : R1 = R2 = R3 = OMe Ar 2 : R1 = R3 = OMe; R2 = OH Ar 3 : R1 = H; R2 = OH; R3 = OMe Ar 4 : R1 = R3 = OMe; R2 = OCH2Ph Ar 5 : R1 = H; R2 = OCH2O = R3 Ar 6 : R1 = H; R2 = R3 = OMe 23 25 O O O O Ar1 OH MeO2C Note: in Roman numeral the synthetic route; in Arabic numeral the bibliographic reference Scheme 3. The main starting materials in the synthesis of aryltetralin lignan analogs of podophyllotoxin. Compounds with rings A and B fused are usually chosen. ISSN 2308-8303 (Print) / 2518-1548 (Online) 8 Журнал органічної та фармацевтичної хімії 2024, 22 (2) for transformations and functionalization, and are the most useful since rings A and B are al- ready fused. From this group of compounds, pi- peronal (20, also known as heliotropin), homopi- peronyl alcohol (21), bromopiperonal (22), asym- metric aryl ketones derived from piperonal (23 and 24), vanillin derivatives (25), piperonyl chlo- ride (26), safrole (27), sesamol (28), 3,4-methy- lenedioxydihydrocinnamic acid (29), phenyl ala- nine (30), and coniferyl alcohol (31) are the most prominent prototypes, in which it is possible to carry out transformations of positions 5 or 6 of ring C (see Scheme 1). Due to their relative abun- dance in nature, few reports have focused on their synthesis during the search for aryltetralin lig- nans. The reports by Urlacher [11] and Sattely [12] are notable since it was possible to synthe- size ring A, to subsequently obtain deoxypodo- phyllotoxin (15) and podophyllotoxin (1) from co- niferyl alcohol or phenylalanine, and a cascade of modified metabolic reactions. Other precursors similar to this group of com- pounds are vanillinic acid and vanillin, which despite lacking ring A, have been used to syn- thesize structural analogs of podophyllotoxin. There are useful methods for forming the 1,3-dioxol ring on phenyl rings: for example, the reaction between 1,2-diphenols (catechols) and methylene bromide [13], methylene chloride [14], or methyl enolates [15]. The reaction of ortho- quinones and imines catalyzed by palladium to obtain substituted 1,3-dioxol rings [16] or ob- taining of piperonal using black pepper pipero- nal synthase has also been reported [17]. The reac- tivity relationships of the positions attached to the aromatic ring between safrole, isosafrole, pi- peronal and sesamol have been studied; starting from catechol, it is possible to find safrole and isosafrole as intermediates until reaching pipe- ronal, from which, in turn, protocols have been described to obtain sesamol [18 – 21]. Regarding alternatives to functionalize the 1,3-benzodioxol system in the search for arylte- tralin lignans, we can generalize two cases: 1. One can take advantage and transform a substituent into the 1,3-benzodioxol system, which carbon will be the position 4 of the aryl- teralin lignan. A side substituent has generally been a benzylic position in the form of carbonyl or primary and secondary alcohol that will become positions 2 and 3. Piperonal (20) and bromopipe- ral (22) (Scheme 2, transformations I to XVI) are the most used reagents for this purpose. In these compounds the carbonyl group is transformed into the secondary alcohol of position 4, also ac- companied by reactions that introduce the car- bons of positions 2 and 3 whether they include ring D or not. Other useful substrates to fol- low this transformation route are those used in transformations VII, XIX, XX, XXI, XXII, XXIII, XXV and XXVII. When it comes to asymmetric syntheses or resolution, this transformation route has served to assemble molecule with the neces- sary configuration in positions 3 and 4. 2. A less studied route starts from 1,3-ben- zodioxols with a substituent that in subsequent transformations would be position 1 of the tetralin- lignan. This is probably because it would involve choosing or preparing a diarylmethanyl system, which means more synthetic steps to reach the corresponding aryltetralin lignan. The formation of these types of bonds is usually designed to occur in the intermediate or final stages of the most of synthetic routes (see Scheme 4). In the litera- ture it is possible to find examples of transfor- mations XVIII and XXI. The methods of constructing ring C As mentioned before, most of the variants for the synthesis of aryltetralin lignans focus on the construction of ring C. This way makes it pos- sible to configure the four stereogenic centers of the lignans. From the pharmacological point of view, variations in positions 1 and 4 have shown good results. In general, the closure of ring C is the final step of a variety of transformations, in which we can distinguish the following three cases: A. dihydroxyester and oxoester strategies – the ring closure through the formation of a diaryl- methanyl bond between position 1 of the tetra- lin system and position 6 of the 1,3-benzodioxol ring (Scheme 4, A); B. the ring closure through Diels-Alder cyc- loadditions (Scheme 4, B); C. the conjugated addition – the ring closure through a cascade of Michael-type reactions and the nucleophilic substitution by α anions (Scheme 4, C). The next three sections focus on the most use- ful examples of these strategies. Strategy A. Dihydroxyester and oxoester strategies One of the first contributions was the work of Curran [22] where the key intermediate was a 1,3-dicarbonyl system (32). Here, the α carbon will become that of position 2 of the tetralin lig- nan, which is also in position β (or position 1 of the tetralin lignan, which is also a benzylic car- bon) has attached to ring E in some of its variants ISSN 2308-8303 (Print) / 2518-1548 (Online) 9 Journal of Organic and Pharmaceutical Chemistry 2024, 22 (2) (see Scheme 3). Thus, with the formation of the bond between position 6 and 1 through two dif- ferent strategies, ring C (33 and 34) is formed (Scheme 5). A strategy similar to that of Curran regard- ing the closure of ring C has been used indepen- dently by Daugan [26], Koga [27], and Uda [28] for the construction of deoxypodophyllotoxin epi- mers (15). The key step of these three transfor- mations is the formation of the two enantiomers of intermediate 35 obtained by resolution and enan- tioselective synthesis. Thus, with the transforma- tion of each enantiomer, the corresponding epi- mer 36 was obtained, and after resolution the epimers of 15 were generated, where the final step of synthesis was the formation of ring C since rings A, B and D were previously incorpo- rated (Scheme 6). Vandewalle proposed the same ring C clo- sure method using protected diols in the form of 1,3-dioxane [29] as a preliminary method and silylene ether (37) [30] integrated into positions 2 and 4 of tetralin. In turn, this substrate con- tains a carbonyl group in position 2. Through the aldol addition to an aryl aldehyde, position 1 and ring E are incorporated. The result is position 2 activated for the nucleophilic substitution (38) by the aryl carbon of position 6 that will close ring C (Scheme 7). As can be seen, 1,3-dicarbonyl-α,β-unsatura- ted systems that have ring E attached to posi- tion β (position 1 of aryltetralin lignan) is a key substrate to carry out this type of the cycle clo- sure. Curran noted this advantage by proposing the Michael addition between the piperonal- derived Michael donor and the Michael accep- tor 39 where the intermediate α anion carried out the intramolecular nucleophilic substitution re- sulted in the formation of ring C of compound 40 (Scheme 8) [31]. A similar strategy was proposed by Zhang [32, 33], in which a piperonal bromine derivative (41) O O Ar O O Ar A O O O O OR X Ar OR Ar R O O R B C O O Ar R R O O Ar R R O O O O Ar1 O O O Ar1 O Scheme 4. The ring C closure strategies in the synthesis of aryltetralin lignans: (A) formation of the bond between positions 6 and 1; (B) the Diels-Alder cycloaddition; (C) the Michael reaction cascade – nucleophilic substitution by enolates O O CO2Et CO2Et Ar 1. 1.3-1.5 equiv (CF3COO)3Ta ClCH2CH2Cl, 84 oC, 30 min 2. Me2SO4, K2CO3, acetone, 12 h O O CO2Et CO2Et Ar1 1.5 equiv NaIO4, EtOH, RT, 2 h ClCH2CH2Cl, TFA O O CO2Et CO2Et Ar2 32 33, 55 % 34, 100 % Scheme 5. The ring C closure proposed by Curran ISSN 2308-8303 (Print) / 2518-1548 (Online) 10 Журнал органічної та фармацевтичної хімії 2024, 22 (2) protected with a chiral pseudoephedrine auxiliary carried out the Michael-type reaction with an ac- ceptor containing ring E (Scheme 9). A sequen- tial process of the Michael addition and nucleo- philic substitution were used to incorporate an allyl group in the α-position to obtain intermedi- ate 42. Its oxidation generated the correspond- ing dialdehyde used further for the cyclization of ring C via the aldol addition to obtain inter- mediate 43. The formation of ring D was carried out via the lactonization to obtain podophyllo- toxone with the subsequent reduction generated the podophyllotoxin enanitomer ((+)-1). The extensive oxoester pathway constructs ring C in the form of a γ-oxoester intermediate 44 (Scheme 10). This strategy was originated by O O Ar5 O Ar5 O CH2OR O O CH2OR 1. LDA 2. Ar5CHO 3. H2/Pd-C 2. IO4 3. CrO3 1. BuLi 2. Ar5CH2CHO 1. Separation 2. Cl2CCO 3. Zn/HOAc 4. Bu3SnH LDA TFA O O Ar5 O Ar5 O CH2OR 1. LDA 2. Ar5CH2Br Ar5 CO2Me CO2H H2 Ar5 CO2Me CO2H 1. Resolution 2. Ca(BH4)2 Koga Dougan Ar1 H O O O (+)-15 O O Ar5 Resolution (-)-35, 64 % (+)-35, 57 % 36a rac-35 1. LiAlH4 O OHO Ar1 Koga O O CH2OR 1. LiAlH4 2. H2, Pd/C 3. IO4 4. CrO3 LDA Ar1 H O TFA O O (-)-15 36a O OHO Ar1 Uda SP MeO O MeO pTol O S pTol O Ar5 Scheme 6. The ring C closure for the synthesis of deoxypodophyllotoxin epimers (15) O CO2TMS Si O O O LDA O CO2H Si O O O Ar1 HO 1. Me3SiCl, Et3N 2. MsCl, Et3N O CO2H Si O O O Ar1 37 38, 34 % Ar1 H O 56 % Scheme 7. The ring C closure via the nucleophilic substitution in position 2 O O O O O 1. 1.2 equiv Ph3P CH + 3Br−, K2CO3, 18-crown-6, THF, 36 h O O Br OCH3 Br 1.05 equiv BuLi, THF -100 oC to RT to 1 h Ar1 CO2Et CO2Et OMe CO2Et CO2Et Ar1 H 39 (1.05 equiv) 40 Br O O OMe CO2Et CO2Et Ar1 Br 77 %, diasteromeric mixture 2. 3 equiv Br2, MeOH, RT, 36 h Scheme 8. The ring C closure using the Michael addition and aldol reaction sequence ISSN 2308-8303 (Print) / 2518-1548 (Online) 11 Journal of Organic and Pharmaceutical Chemistry 2024, 22 (2) Gensler (Route A) [34] with the construction of ring C through the aldol condensation between diaryl ketone 45 and diethyl succinate to gene- rate 46, upon which the ring closure was carried out via the Friedel-Crafts type acetylation. Rogers designed γ-aryllactone 48, which enolate carried out the addition-elimination on piperonyl chlo- ride 47 and generated intermediate 49, which, af- ter the rearrangement and decarboxylation (50), gave the oxoester intermediate (Route B) [35]. For their part, Wattanasin [36] and Doyle [37] (Route C) proposed the formation of trisubstituted cyclopropyl intermediate 52 from α,β-unsaturated piperonyl ketones 51 for constructing the corre- sponding oxoesters 44. Curran (Route D) also pro- posed the formation of type 44 oxoesters in two independent methodologies. The first is based on his own previous contributions from the 1,3-di- carbonyl system (32) [38], and the second from a methoxybromide (53) derived from piperonal to generate 55, a structural analog of 33 [29]. Strategy B. Addition via the Diels-Alder reaction Another route for the construction of ring C is through the Diels-Alder reaction remained in force for almost 50 years. One of its advantages is that it allows almost all alternative configurations of the tetraline system to be addressed. From the synthetic point of view, the diene occurs in a va- riant of the system that already contains the methylenedioxyphenyl nucleus (rings A and B), either as a resonance hybrid or as a formal structure O O N O Ph Br OtBu O Ar1 O O OtBu O 42, 65 % Ar1 O O O OtBu OAr1 O O O O OtBu OAr1 OH OH O O OtBu OAr1 O OH O O O OAr1 O nBuLi, THF, -78 oC, 0.5 h TMEDA, 1.5 h OsO4, NMNO tBuOH/THF/H2O 94 % L-proline, CH2Cl2 then NaBH4, MeOH 81 % O O O OAr1 OH (+)-1, 98 % L-selectride HCl/H2O, MeCN 41 43, 80 %90 % allyl bromide, RT, 2 h then AcOH/H2O in THF then NaIO3/SiO2 CH2Cl2, RT MnO2 MeCNthen DCC in CH2Cl2THF, -78 oC Scheme 9. The synthesis of podophyllotoxin and its enantiomer proposed by Zhang O O O Ar O O O CO2Et Ar O O CO2Et CO2Et Ar2 O O CO2Et CO2Et Ar2 O O CO2Et CO2Et Ar2 OMe O O Li Br OMe CO2Et Ar2 CO2Et + 1. Tl(O2CCF3)3 2. NaHSO3 3. Me2SO4 1. NBS/H2O 2. OH−/MeOH O O O CO2Et Kende Ar1 Et2O BF3 or SnCl4, MeNO2 1. H2, Pd/C 2. AcCl 3. SnCl4 O O Ar1 O CO2Et CO2Me SnCl4, CHCl3 RT, 12 h 1. TFA, NaHCO3 2. CeO3/Py 3. OH−/MeOH 50, 91 % O O Ar CO2Et CO2EtEtO2C CO2Et KOtBu Ar1EtO2C O O Cl O + Ar1 OEtO2C MeO2C O CO2MeKO2C Mn(OAc)3 2H2O AcOH, 70 oC KH, THF Route B 44 O O O Ar1 Route C 45 46 Route A 47 48 49, 80 % 51 32 55, 55 % 5354, 88 % Route D 66-100 % 53-95 % 60 % 50 % * RT, 24 h O O O Ar1 O EtO2C CO2Me O Me2S CO2Et * 52, >90 % Scheme 10. The oxoester pathway in constructing ring C of aryl tetralin lignans ISSN 2308-8303 (Print) / 2518-1548 (Online) 12 Журнал органічної та фармацевтичної хімії 2024, 22 (2) that is in equilibrium with a precursor. Thus, the most notable contributions offer alternatives for the design of dienophiles that allow the con- struction or almost complete incorporation of rings D and E. For the purposes of studying the Diels-Alder pathway, we can divide the contributions into intermolecular reactions (Scheme 11) and in- tramolecular reactions (Scheme 12). Many in- termolecular methods use dimethyl fumarate or its analogs as dienophiles, in which precursors of aryltetralin lignans are obtained where rings A, B, C, and E are already included, and ring D will be formed later. Thus, one of the first contri- butions was proposed by Rodrigo [39] through the formation of an isobenzofuran ring substi- tuted in position 1 with ring E (56). This system functioned as a diene and reacted with dimethyl acetylenedicarboxylate (DMAD, 57) generating an adduct already containing the aryltetralin- lignan system (58). This adduct was also formed by Berkowitz by a similar synthesis route [40]. O O Br 1. BuLi 2. Bu3P CuI O O CHO O O OH CH2OH Ar1 CO2Me Diene Dienophile O O Ar1 OH h� OMe OMe O O O O Ar Glinksi et Durst (1983) O O O Ar Jones et Thomson (1987 et 1994) CO2Me CO2Me O O AcOH O O Ar1 OMe OH Rodrigo (1980) Ar1 OMe O OMe OO MeO O O Ar CO2Me CO2Me O O O SO2 Ar O O CH2SiMe3 OH Ar O O Ar OO O O O O OAr O Ogasawara (1985) O O Ar1 OH O O Ar1 OH O O CO2Me Ar CO2Me HO Charlton (1995) MeO O OMe O MeO O OMe O MeO O OMe O O O OH Ar1 O O tBu O O O O Ar1 OH O O tBu O Choy (1990)O O OAc Ar1 56 57 58 59 60 61 62 63 64, 58 % 65 66 67, 64 % 69 68 70, 62 % O O O OTBS 71 O O OTBS ArH2N O OMe O Ar = C6F4(4-CF3) O O CO2Me OTBS NHAr OMaimone (2014, 2019) 72 73 O O Br OMe OMe Berkowitz (1996) * 3. ArCH2Br 4. H3O+ Ar1 Scheme 11. Examples of an intermolecular Diels-Alder reaction in the synthesis of aryltetralin lignans ISSN 2308-8303 (Print) / 2518-1548 (Online) 13 Journal of Organic and Pharmaceutical Chemistry 2024, 22 (2) Another method was proposed by Durst [41] forming a diene via irradiation promoting the tautomeric equilibrium between a piperonal de- rivative and the corresponding enol (59). The latter when reacting with dimethyl fumarate generates the adduct with ring C formed (60). This pro- duct and its analogs and precursors were also obtained by Thomson [42, 43] in his strategy from a diene in the form of isochromenone (61) which also reacts with dimethyl fumarate. Charlton [44] for his part, used benzocyclobu- tanol (62) to form an enol-type diene (63) reacted with dimethyl fumarate to generate a product similar to the Durst’s substituted with a hydroxyl group in position 1 (64). The last two intermolecular Diels-Alder stra- tegies employ α,β-unsaturated cyclopentacarbo- nyls as dienophiles. This alternative has the ad- vantage that the products obtained are tetralin lignans, analogs of podophyllotoxin with the five integrated rings. Ogasawara [45] used maleic an- hydride (66), which, when reacted with dimethy- lenecyclohexa-1,3-diene (65), generated the deoxy- podophyotoxin analog 67. In this methodology, it is notable how the diene can be obtained from two different substrates. Choy [46] used a dienophile integrated with a chiral auxiliary (R)-(4-oxocyc- lopent-2-en-1-yl)methyl pivalate (69), meanwhile the diene (similar to 59) was generated in a stra- tegy similar to that of Charlton frombenzocyclo- butanol (68). In this case, the product obtained was a mixture of picropodophyllotoxin epimers (70). Finally, the Maimone’s [47, 48] strategy used benzocyclobutanol 71 and the fumarate deriva- tive 72 to obtain product 73 similar to 60. Although the intermolecular Diels-Alder re- actions for constructing podophyllotoxin and its analogs are the most versatile and widespread, first the corresponding intramolecular variants were developed. A generic example is represented by the synthesis of lignan lactones 75 via the Diels-Alder reaction in which both the diene (E-propyl styrene system) and the dienophile (an α,β-unsaturated ester that in the β position is linked to the corresponding E ring) are present in the same substrate (74) [49 – 53]. It highlights the synthesis of the substrates through the classical Fischer esterification [54] and various ways of ac- tivating the corresponding Diels-Alder addition, such as microwave irradiation [55]. This stra- tegy has been used to synthesize tetralin lig- nans, such as taiwanin (76) and justicidin (77) (Scheme 12) [56]. Thus, proposals for the synthesis of podophyl- lotoxin through an intramolecular Diels-Alder re- action have been presented regularly. Durst and Speltz reported two strategies. From carbama- tes (78) [57, 58] and carbonates (79) [59] they ge- nerated dienes similar to those prepared by Choy and Charlton (80 and 81) and cyclized to generate ring C (82 and 83, Scheme 13). Czarnocki [60] also provided his version of a periciclic reaction to form ring C using proli- nol as a chiral auxiliary. Intermediate 84 under- went an electrocyclic reaction that generated com- pound 85 (Scheme 14). Strategy C. Conjugate addition Another widely used and standardized metho- dology in constructing ring C is activating posi- tion 4 as a nucleophile. This strategy can be car- ried out through α-carbon reactions, Knoevenagel- type reactions, or activations via the Corey-Seebach or other umpolung reactions, which have been the most efficient and selective in this group of transformations. Starting from piperonal (20), the general strategy is that described in all the proposals of Scheme 15 [61]. The carbonyl of piperonal (po- sition 4) is activated as a nucleophile (86), which acts as a Michael donor with α,β-unsaturated furan-2-one (87) which can be substituted with a chiral auxiliary in the γ position (R3). Once the O O OH Klemm (1963 – 1966) O O O O Ar1 O O O Ar1 O O O O O O O taiwanin 7574 O O O O O justicidin O 76 77 Scheme 12. The example of the intramolecular Diels-Alder reaction in the synthesis of aryl-tetralin lignans ISSN 2308-8303 (Print) / 2518-1548 (Online) 14 Журнал органічної та фармацевтичної хімії 2024, 22 (2) 1,4-addition is made, the corresponding enolate acts as a nucleophile for the aldol addition with an aryl aldehyde or a benzyl halide that already contains the corresponding E ring. Thus, the ge- neric product of this transformation is a system of two phenylpropanoid units (88, similar to 3) bonded by their carbons 8 and 8’ (positions 3 and 2 of the tetralin lignan, respectively). This sys- tem has the dithiane group in position 4, while in position 1 it may have a hydroxyl group (R4), depending on whether there is the aldol addi- tion or the nucleophilic substitution. The subsequent transformation consists of the release of the dithian group to generate a methy- lene (89, Route A), a methine-hydroxyl group (90, Route B) or a keto group (91, Route C) in po- sition 4. The ring closure is carried out via the nucleophilic substitution from position 6 to 1 to generate the analogs of deoxypodophyllotoxin (92), podophyllotoxin (93), and podophyllotoxone (94). O O Ar1 O N O O O O Ar1 O N O O H MeOH/TFA O O Ar1 O N O O [1,5]-H shift 84 85 Scheme 14. The intramolecular Diels-Alder cycloaddition using prolinol derivatives as a chiral auxiliary O O SR2 SR1 O O O O SR2R1S O O Ar R4 R3 ArCHO or ArCH2Br O O O O Ar R4 O O O O Ar R4 O O OH O O Ar R4 O O O O OAr O O O O OAr O O O OAr OH A B C D E F G 86 87 88 89 90 91 92 93 94 R3 Scheme 15. The general scheme of the conjugate addition method for the synthesis of aryl-tetralin lignans O O OAc Ar1 O O O O Ar1 H N CO2Me 1.LiOH, H2O 2. heating O O O NH CO2Me Ar1 MeO2C NCO Ph3SnOAc O O NHO CO2Me Ar1 O O O O O O Ar1 O CO2Me O O OO CO2Me Ar1 O O O O O CO2Me Ar1 O 78, 47 % 79 80 81 82 83 Scheme 13. Intramolecular Diels-Alder reactions using benzocyclobutanes as diene precursors ISSN 2308-8303 (Print) / 2518-1548 (Online) 15 Journal of Organic and Pharmaceutical Chemistry 2024, 22 (2) The first two examples of this methodology were the works by Ziegler [62] and González [60, 63] (Scheme 16) where through dithiolanes (86a) the hydroxyl-lignans 88a and 88b were ob- tained, their ring C closure was reported to ob- tain the corresponding epimers: epipodophyllo- toxin (12), picropodophyllotoxin (13), podophyll- otoxanes (94a – c). In the 1970s, Ziegler provided evidence to conclude that only 1,3-dithyan nu- cleophiles could carry out the corresponding Mi- chael addition; however, years later Iwasaki and Ward improved the use of 1,3-diketones or α-cyano- esters (see Schemes 22, 23 and 24). For his part, Ward [64] used this same methodology from thio- phenylacetals (86b) when constructing epimeric de- rivatives of podophyllotoxin 95, from ketone 91a. Later Ward also showed the option of em- ploying a single thioether substituent (86d,e) to obtain analogs of desoxypodophyllotoxin (92a) and epipodophyllotoxin (93a) (Scheme 17). In the early 1990s, Kutney [65] made two out- standing contributions to the synthesis of inter- mediates similar to 88 lacking ring A. The first was the use of benzyl halides as a source of ring E (Scheme 18; 88f and 88g); intermediates 89a, 89b and rac-90d and rac-90e were obtained from them. The second contribution consisted of the latter being reacted with a peroxidase with cata- lytic promiscuity from Catharanthus roseus plant, which had already made similar ring closures. Thus, the closure of ring C could be achieved in intermediate 89a to generate 92b and (S)-90e to generate 93b. A similar method to that of Scheme 16 was developed by Bhat [66], in which instead of a thio- acetal, phenylsulfoxide 86h was used as a nu- cleophile to subsequently follow the Pelter-Ward route (Scheme 19). It is noteworthy that it was possible to synthesize podophyllotoxin (1) in just a few steps of synthesis. One of the strategies to control the diaster- oselectivity of type 88 compounds was to incor- porate a menthyl group (in its two configura- tions) as a chiral auxiliary in furanone 87 (87b) (Scheme 20) and react it with the correspond- ing anions of thioketals (86i) [67 – 70] and dithio- lanes (86j) [71]. The idea of including chiral auxiliaries in ty- pe 87 furanones was originally proposed by Koga and his collaborators [25, 72]. In the similar syn- thesis to those previously explained, dithiane 96 (ring E activated as dithiane) was used to carry out the Michael type addition on lactone 87c and obtain the activated intermediate 97, a phe- nylpropanoid system with rings D and E joined through positions 1 and 2 (Scheme 21). In this case, rings A and B are integrated as piperonyl bromide through a nucleophilic substitution to O O O Ar O O + O O O Ar O O + 12 + 13 O O O Ar O R2R1 HO O O O Ar1 OHO O O O O Ar1 OHO OH O O O Ar1 O OBzO OO O R2 R1 Ziegler and González, 86a: R1 = S(CH2)3S = R2 Pelter, 86b: R1 = R2 = SPh Ziegler: Ar1CH2Cl González: CHOAr6 Pelter and Ward: CHOAr1 87a Ziegler, 88a: R1 = S(CH2)3S = R2; Ar1; 93 % (52/48 eritro:treo) González, 88b: R1 = S(CH2)3S = R2; Ar6; 66 % (isomers mixture) Pelter, 88c: R1 = R2 = SPh; Ar1; 97 % (eritro/treo mixture) Pelter NIS Ziegler, 94a; Ar1; 90 % González, 94b; Ar6 Ziegler and González, only treo 94c 91a, 85 % 90a, 55 % 95 Scheme 16. First examples of the conjugate addition as a synthesis method of aryltetralin lignans Ar1CHO O O O O Ar1 HO SR 1. Ni Raney 2. TFA O O O OAr1 HClO4 O Ar1 OH O O O O SR Ar1 O O O 86d: R = Ph 86e: R = tBu O O SR O O + 1. Hg2+ 2. H2O88d,e 50 % 92a, 60 % 93a, 60 % 87a Scheme 17. The synthesis of deoxypodophyllotoxin (85) and epipodophyllotoxin (86) from thioethers derived from piperonal ISSN 2308-8303 (Print) / 2518-1548 (Online) 16 Журнал органічної та фармацевтичної хімії 2024, 22 (2) R2O R1O SPh SPh O O + Ar4CH2Br R2O PhS SPh O O Ar4 1. I2, MeOH 2. HCl/THF R1O R2O O O Ar4 O R1O R2O O O Ar4 OH H2, Pd/C 1. BCl3 2. CaCO3 R1O R2O O O Ar2 OH R1O R2O O O Ar2 R1O R2O O OAr2 R1 = H; R2 = Me R1O R2O (S) O O Ar2 OH R1O R2O O O Ar2 Catharanthus roseus pH 6.4, H2O2 R1 = H; R2 = iPr OH Catharanthus roseus pH 6.4, H2O2 86f: R1 = H; R2 = Me 86g: R1 = H; R2 = iPr 87a 88f: R1 = H; R2 = Me 88g: R1 = H; R2 = iPr 89a: R1 = H; R2 = Me 89b: R1 = H; R2 = iPr 92b: R1 = H; R2 = Me 91b: R1 = H; R2 = Me 91c: R1 = H; R2 = iPr 90b: R1 = H; R2 = Me 90c: R1 = H; R2 = iPr rac-90d: R1 = H; R2 = Me rac-90e: R1 = H; R2 = iPr (S)-90d: R1 = H; R2 = Me (S)-90e: R1 = H; R2 = iPr 93b: R1 = H; R2 = Me R1O only; only; Scheme 18. The closure of C ring using the enzymatic catalysis with peroxidase from Catharantus roseus O O S Ar1 O O O O PhO O O O H 4 steps S PhO HO 1, 25 % 86h 60 % 1. TFA, 0 oC, 3 h 2. HgO, BF3 OEt2, 28 h 1. nBuLi, THF -78 oC, 1 h 2. 79a, 1 h 3. Ar1CHO, THF, 2 h * Scheme 19. The synthesis of podophyllotoxin using phenylsulfoxides O O R2 R1 O O + Omenth Ar1CHO O O O O R1 R2 Ar1HO Omenth 1 NiCl2, NaBH4 2. NaBH4, NaOH O O O OArHO TFA Pelter, 86i: R1 = R2 = SPh O O O O ArHO O O O O O Si CO2Me Ar HO (-)-12, 81 % Pelter Vandewalle Vandewalle, 78j: R1 = S(CH2)3S = R2 87b (-)-15 KOH, NaBH4O O O O R1 R2 Omenth O O O O R1 R2 Ar1HO O O O O R1 R2 84 % 1. LDA 2. Ti(NEt2)3Cl 3. Ar1CHO HgCl2 CaCO3 83 % 81 % 86 % ~60 % Scheme 20. The conjugate addition using chiral menthyl auxiliaries in furanones ISSN 2308-8303 (Print) / 2518-1548 (Online) 17 Journal of Organic and Pharmaceutical Chemistry 2024, 22 (2) obtain 98. The removal of the ester, benzyl and dithiane groups generated lignan 99, which sub- sequent oxidation generated (+)-burseran (100), a direct precursor of an epimer of deoxypodo- phyllotoxin. As mentioned above, Ziegler studied the ac- tivation of position 4 as a nucleophile by placing it in the α-position of thioacetals and carbonyl systems; however, the latter did not generate good results in the synthesis of podophyllotoxin- type lignans at the time (Scheme 22). This technique was later improved by Iwasa- ki [73] and Ward [74] by implementing TBS-type protecting groups in position 4 (86k) and thus obtaining 88h-type compounds (Scheme 23, A). The second stage of this methodology was proposed by Enders [75, 76] and his collaborators by incorpo- rating secondary amines as chiral auxiliaries (86l), preserving the nitrile group (Scheme 23, B). The Michael-type addition of the corresponding nucleophile proceeded with diasteromeric excess- es of up to 98 %. The subsequent removal of the auxiliary and the aldol condensation with differ- ent aldehydes reached 88 % yield and up to 96 % enantiomeric excess for compound 91d. The use of menthol as a chiral auxiliary has also been implemented in this methodology. Storer [77] reacted α-anion 86m with ketone 87b to obtain 88i, which could be oxidized to ketone 91e and reduced to alcohol 90f (Scheme 24). Recently, Hazra [78] provided a new metho- dology for the formation of type 88 (88j) interme- diates through aldol-type reactions with bromo- piperonal (22) and in situ formation of D ring (Scheme 25). This compound was cyclized to form intermediate 90g from which it was possible Ar1 S S + OBn O O Ar1 S S OBn O O 87c96 97 O O Br Ar1 SS OBn O O 98, 96 % O O Ar1 OH OH OH 99, 98 % O O Ar1 O O 100, 85 % O O THF Ni-Ra LiAlH4, THF tBuOH, NaIO4 Scheme 21. The first inclusion of chiral auxiliaries in the conjugated addition for the synthesis of lignans O O R2 R1 O O Ar O H O O R2R1 O O Ar86 87 88 a) No reaction R1 = R2 = CO2Me b) No reaction R1 = CN; R2 = OCH(OEt)CH3 c) No reaction R1 = CN; R2 = N(CH2CH2)2 d) No reaction R1 = H; R2 = SOPh e) No reaction R1 = R2 = SEt f) Reaction proceeds R1 = R2 = S(CH2)3S Scheme 22. Proposals for activation of position 4 in the α-carbon form of carbonyls and thioacetals O O OTBS CN O O Ar1 O H O O OTBSNC O OAr1HO 86k 88h, 84 % O O N CN O OPh O O N NC O O O OPh O O O OAr1HO 91d, 54-88 % O Ar = a) Ar1; b) piperonyl; c) p-anisyl; d) veratryl 86l 94-98 % 56-58 % de THF or Et2O, LDA -78 oC, 87a 60-98 % de, >96 % ee 1. tBuLi, THF, -78 oC, ArCH2Br or ZnCl2, Ar1CHO, NH4Cl, H2O 2. AgNO3, H2O, THF, TA 87a A B Scheme 23. The activation of position 4 through α anions of nitriles ISSN 2308-8303 (Print) / 2518-1548 (Online) 18 Журнал органічної та фармацевтичної хімії 2024, 22 (2) to differentially obtain podophyllotoxin (1) and two of its epimers (–)-13 and (+)-13. The synthesis of podophyllotoxin and analogs reported by Fuchs [79] could also be included in the conjugate additions. The reaction of pipe- ronal with bromomethylfuranone (87d) yields rac-trans-101, which after the Michael type ad- dition generates rac-trans-90a (hydroxyyatein) from which racemic yatein 16 could be formed (Scheme 26). It highlights the integration of a biocatalytic protocol using the enzyme 2-ODD-PH to carry out the formation of cycle C and the ste- reoselective obtaining of hydroxyyatein (+)-90a. Renata [80] also used the enzyme 2-ODD-PH in the cyclization of yatein (16), it was prepared via cross-heterocoupling of enolates of compounds 102 O O OTBDMS NC O O Ar1 O H O O OTBDMS NC O OAr1HO 86m 88i Omenth Omenth TBAF O O O OAr1HO OmenthO O O O OAr1 HO OH NaBH4 91e 90f 87c Scheme 24. The use of menthol as a chiral auxiliary in the conjugate addition of alpha anions to nitrile O O H O Br MeO H O O + O O OH Br O O 1. L-proline (cat.) DMF, 4 oC, 24 h then NaBH4, MeOH, 0 oC, 2 h 2. pTSA, toluene, 65 oC, 8 h O O OTBS Br O O TBSOTf THF, 0 oC, 12 h O O OTBS Br O O 1. LiHMDS, Ar1CHO THF, -78 oC, 6 h 2. MsCl, Et3N 0 oC to RT, 4 h then DBU, rt, 12h 22 88j, 84 % Pd, DMF, DIPEAO O OTBS O OAr1 O O OTBS O O + 1, 54 % (-)-13, 52 % (+)-13, 88 % 1. Pd/C, HCO2Na, H2O 1-pentanol, 40 oC, 12 h 2. TBAF, AcOH-THF 0 oC, 2 h 1. Pd/C, HCO2Na, H2O 1-pentanol, 40 oC, 12 h 2. TBAF, THF RT, 2 h 1. Pd/C, H2 (1 atm) MeOH, RT, 12 h 2. TBAF, THF, 0 oC, 2 h 94 % 90g, 84 % Ar1 80 oC, 12 h Scheme 25. The alternative in the synthesis of lignans by the conjugate addition O OBr O O H O + O O OH O O H rac-trans-101 Zn0, NH4Cl toluene/DME, RT 20 87d O O OH O O H rac-trans-90a O B O Ar1 Ar1 H [(RhIcod)Cl]2, Et3N, 1,4-dioxane/H2O, 70 oC, 3 h rac-16, 95 % H2, Pd/C, HClO4 2-ODD-PH FeII, Na ascorbate TRIS (pH = 7.4), 18 oC O O OH O O H (+)-90a Ar1H +12, 38 % >99 % ee Scheme 26. Obtaining hydroxyyatein and epipodophyllotoxin via an alternate conjugated addition from piperonal ISSN 2308-8303 (Print) / 2518-1548 (Online) 19 Journal of Organic and Pharmaceutical Chemistry 2024, 22 (2) and 103 from which dehydroxypodophyllotoxin (15) was subsequently obtained (Scheme 27). A strategy that shares the same reasoning as the conjugate additions described so far is the Bach’s [81] strategy, in which the formation of ring C is the critical step in the podophyllotoxin synthesis. Starting from (3,4,5-trimethoxy)-benzal- dehyde and vinylfuranone 104, rings D and E were incorporated via the aldol addition to sub- sequently incorporate the piperonyl group via the Friedel-Crafts alkylation to obtain interme- diate 105. With the formation of the correspond- ing ring C a 4-exovinylpodophyllotoxin (106) could be generated, its reduction generated po- dophyllotoxin (1) (Scheme 28). The synthesis of ring D The synthesis of ring D in aryl-tetralin lig- nans of the podophyllotoxin type and their struc- tural analogs is a poorly differentiated topic in dis- cussions of the total synthesis of these compounds. The main methods consider that the most criti- cal transformations are those that allow the synthesis of ring C with the proper configura- tion of its four tetrahedral carbons and that the synthesis of ring D is usually easier to carry out, either as an intermediate or final step. Although in most methods the formation of ring D is rela- tively simple, it is worth pointing out some pe- culiarities in this regard. Incorporation of preformed rings The simplest method to obtain ring D is its incorporation through a precursor that already contains it (Scheme 29). The works of Koga, Daugan and Uda mentioned in Scheme 5 and the general strategy of the conjugate addition in Scheme 12 are examples of this methodology. Another way to reach this ring is through the Diels-Alder type intramolecular cycloadditions pro- posed by Klemm, described in Scheme 12. In this strategy, the ester group, which will later be the O O O O O O Ar1 αKG, 2-ODD-PH O2, Fe2+ O O O O 15, 95 % Ar1 Y* O OAr1 OtBu O O Y* O N O O iPr Y* = Ar1 OtBu O LDA, CuII LiBH4, DBU, ∆ 1, 58 % 1. CrO3, 3,5-DMP 2. L-Selectride 16, 51 % 102 103 + Scheme 27. The synthesis of yatein, deoxypodophyllotoxin and podophyllotoxin implementing the enzymatic cyclization and cross-heterocoupling O O O O OH H O Ar1 + O O HO Ar1 O OAr1 O O OH O OAr1 O O OTf O OAr1 O 1, 75 % 1. OsO4, NMO NaIO4, CH2Cl2 2. LiAlH(OtBu)3 Et2O O Pd(OAc)2, PPh3 Tf2O, NEt3 89 % LDA, THF AuCl3, CH3NO2 20 oC, 1 h 104, 94 % 105, 98 % 106, 58 % -78 oC, 30 min CH2Cl2MeCN Scheme 28. The podophyllotoxin synthesis through a 4-exovinyl-podophyllotoxin formed via the Friedel-Crafts acylation O O R O O Ar O O O OAr Koga, Daugan and Uda conjugated addition Scheme 29. The incorporation of ring D through precursors that already have formed it ISSN 2308-8303 (Print) / 2518-1548 (Online) 20 Журнал органічної та фармацевтичної хімії 2024, 22 (2) lactone, is already formed, and the cycloaddition will complete the formation of rings C and D (Scheme 30). Lactonization When the incorporation of the complete D ring is not possible, a strategy that is convenient due to its simplicity and variety of conditions is the formation of the lactone-type bond from precur- sors that have a hydroxymethyl group or its syn- thetic equivalent in position 3 and an acid deriv- ative in position 2. Thus, we can find examples where the synthesis of ring D is the last step to synthesize podophyllotoxin (Scheme 31) or to ob- tain its analogs or precursors of it (Scheme 32). Thus, we can find the contributions of Rodrigo, [82, 83] Trujillo,[60, 62] Curran, [23] Koga, [25] Wattanasin, [84] Takano, [44] Wong, [85] Durst, [40, 56, 57] Vandewalle, [70] Thomson, [42] Charlton, [43] Meyers, [86] and Zhang [30, 31, 79]. It is possible to find variants where ring D is formed before incorporating other rings as in the case of Hazra [25]. Sherburn [87] reported an interesting case of the formation of ring D, and the incorporation of ring E. Starting from vinyl piperonal 27 and cro- tonyl-oxazolidinone 107, the aldol reaction pro- duct 108 was obtained, its chiral auxiliary re- lease generated 109. The formation of ring C was through the metathesis to generate tetralin 110. The key to forming rings D and E was the incorpo- ration of a thiocarbonate group (111). Thus, the epimeric protein derivative of podophyllotoxin 112 R1 R2 O O Ar Ac2O O OAr R2 R1 + O OAr R1 R2 H2, Lindlar catalyst H2, Pd/C R1 R2 O O Ar O OAr R1 R2 a) R1 = R2 = H b) R1 = R2 = -OCH2O- , Ar1 c) R1 = R2 = -OCH2O- , Ar4 d) R1 = R2 = CH3O, Ar4 e) R1 = R2 = CH3O, Ar = Ph f) R1 = R2 = R5 = H, Ar4 Ac2O Scheme 30. The ring D formation by the intramolecular Diels-Alder addition O O OMe OAr1 OH O O O O OAr1 OH Ra-Ni Rodrigo (1989) O O Cl Ar4 O NaO O O OMe OAr4 O DMF Trujillo O O OMe OAr4 OH ZnCl2 Thomson OH TBAF, ZnCl2 Vandewalle O Si tButBu O O CO2H Ar1 NHO O LiOH H+, HNO2 Durst O O Ar1 OH O O Ar1 O O OH 3. DCC Wong 1. OH− 2. H+OMe O OH Durst (1982) O O Ar1 O OH O O O O O O Ar4 HO Rodrigo (1981) O O OtBu OAr1 O OH O O O OAr1 O L-selectride THF, -78 oC HCl/H2O, MeCN then DCC in CH2Cl2 Zhang + Scheme 31. The ring D synthesis via esterification to form lactones to obtain podophyllotoxin ISSN 2308-8303 (Print) / 2518-1548 (Online) 21 Journal of Organic and Pharmaceutical Chemistry 2024, 22 (2) could be transformed into a podophyllotoxone (113), podophyllotoxin ester 114 and in podophyllotox- in epimer 115 (Scheme 33). Within the variety of options around ring D, it is possible to find that analogs have been proposed with a change in the position of the lactone function (referred to in this context as retrolactone: 117 and 118, Scheme 34A) [58, 59], a greater number of atoms forming the ring (Scheme 34B), [88] of saturated heterocycles (Scheme 34C), [66, 89] or in different positions (Scheme 34D) [90]. ■ Conclusion Taking podophyllotoxin as a natural prototy- pe (1), the synthesis of aryltetralin lignans con- tinues to be a topic of interest due to their poten- tial as therapeutic agents. During the last seven decades, the variety and quantity of works refer- ring to the synthesis of these compounds have been so enriched that methodological classifica- tions have been organized and have made it easier to understand the state of progress of this area of knowledge. The present bibliographic review O O CO2H Ar1 X CH2O, NaOH O O Ar1 X O O O O CO2H Ar1 CO2H (CF3CO)2O O O Ar1 O O O NaBH4 O O CO2H Ar1 OH OH H Charlton Curran (X = OH) Wattanasin (1982) (X = (C)=O) O O Ar1 OH O O Ar1 O O OH 1. NaIO4 2. CrO3 Koga Charlton and Ogasawara O O OH OH Br OH O pTSA, toluene 65 oC, 8 h Hazra O O O Br OH O 15 Scheme 32. The ring D synthesis via esterification to form lactones and analogs and precursors of podophyllotoxin O O O OAr1 OTBS MeOH, H2SO4 25 C, 2 h O O H O Y* O N O O Bn Y* = + O O TBSO Y* O O O OTBS OH O O OTBS OHO O OTBS O SO Ar1 O O OMe OAr1 O OH O O O OAr1 OH 27 107 108, 78 % 109, 94 % 110, 91 % 1. Bu2BOTf, NEt3, CH2Cl2, -78 oC to 0 oC, 1 h 2. H2O2, Et2O, 25 oC, 14 h 3. TBSOTf, 2,6-lutidine, CH2Cl2, 25 oC, 0.5 h NaBH4 (15 equiv) THF/H2O, 25 oC, 12 h Grubbs catalyst, CH2Cl2, 25 oC, 2 h pyridine, CH2Cl2 25 oC, 2.5 h 111 , 89 % Cl S O Ar1(Me3Si)3SiH, AIBN PhH, 80 oC, 8 h nBu4NF, AcOH, THF, 25 oC, 8 h 112, 38 % PCC, CH2Cl2, 25 oC, 5 h 1. DBU, THF, 25 oC, 6 h 2. LiEt3BH, THF, -78 C, 1 h SiO2, MeOH, 56 C, 2 hO O O OAr1 O 113, 96 % 114, 96 % 115, 81 % 3. ZnCl2, sieves, THF, 2.5 h o o o Scheme 33. The ring E incorporation and the ring D formation in the synthesis of podophyllotoxin and podophyllotoxone epimers ISSN 2308-8303 (Print) / 2518-1548 (Online) 22 Журнал органічної та фармацевтичної хімії 2024, 22 (2) has proposed a new classification focused on how to synthesize and functionalize the five rings of podophyllotoxin and its structural analogs, which will give the opportunity for synthetic and pharmaceutical chemistry groups to have a guide for optimizing already existing compound synthesis, as well as proposals from other repre- sentatives of this family. ■ References 1. Seegers, C.; Setroikromo, R.; Quax, W. Towards Metabolic Engineering of Podophyllotoxin Production. In Natural Products and Cancer Drug Discovery, Farid, A. B., Ed. IntechOpen: Rijeka, 2017. https://doi.org/10.5772/67615. 2. 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Chem. 2013, 25 (17), 9555 – 9557. https://doi.org/10.14233/ajchem.2013.15073. Information about the authors: Francisco Flóres-Hernández is bachelor’s degree applicant in Chemistry, Pharmacy, and Biology, University of Guadalajara (México). Tania Isabel Zárate-López earned a bachelor’s degree in chemistry, Pharmacy, and Biology at the University Colima (2020). As a PhD student in Biotechnological Processes at the University of Guadalajara (México), she developed chemoenzymatic and friendly environmental synthetic methods for the preparation of aryl-tetralin lignans reported in the thesis “Development of a Method for Synthesis of Podophylotoxin and Related Aryl-tetralin Lignans, Implementing Chemo-enzymatic and Green Chemistry Strategies”. https://orcid.org/0000-0002-1766-3682. Marco Antonio Alcaráz-Cano earned a bachelor’s degree (2021) in Molecular Design and Nano-Chemistry at the Chemical Research Center (CIQ) of the Institute for Research in Basic and Applied Sciences (IICBA) at the Autonomous University of the State of Morelos (UAEM), with a thesis «Review of Synthesis Methods for Podophyllotoxin Reported from 2000 – 2021» under the supervision of Dr. Jaime Escalante. He is currently a master’s degree applicant in the Laboratory of Nanochemistry and Nanocarbon under the supervision of Dr. María Luisa García Betancourt at the Chemical Research Center (CIQ) – UAEM. https://orcid.org/0000-0003-1754-0751. Jaime Escalante studied chemistry at the UNAM in Mexico City (1985), received a M.Sc. (1991) and Ph.D. (1995) from CINVESTAV-IPN, Mexico City, with a thesis on Asymmetric Synthesis of β-amino acids (supervisor E. Juaristi). Following a post-doctoral stay at the University of Illinois at Chicago, USA (with D. Crich). Later, he returned to Mexico, where he is now a Professor of Chemistry at the Chemical Research Center of Autonomous Morelos State University. He has also served as a Visiting Professor at ETH-Zurich. https://orcid.org/0000-0001-5485-0244. José Domingo Rivera-Ramírez (corresponding author) received a PhD in 2015 with a dissertation on the mechanism of selectivity of lipases mediated by the polarity of solvents. From 2014 to 2018, started to work on Signa-Apotex Inc. in the R&D department. In 2018, he moved to the University of Guadalajara (México) as assistant professor. In 2020, he founded the Laboratorio de Química Farmacéutica. His current research lines are focused on the synthesis of lignans and capsaicinoids employing green methodologies and in the elucidation of promiscuous enzymatic mechanisms. https://orcid.org/0000-0003-3188-7321; e-mail for correspondence: domingo.rivera@academicos.udg.mx.
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spelling oai:ojs.journals.uran.ua:article-3089422026-08-23T16:14:17Z Podophyllotoxin and Aryltetralin Lignans: Methods for the Synthesis of Rings A, B, C, D Подофілотоксин та арилтетралінові лігнани: методи синтезу кілець A, B, C, D Flores-Hernández, Francisco Zárate-López, Tania Isabel Alcaráz-Cano, Marco Antonio Escalante, Jaime Rivera-Ramírez, José Domingo lignans podophyllotoxin aryltetralin-lignans etoposide teniposide лігнани подофілотоксин арилтетралінові лігнани етопозид теніпозид Podophyllotoxin, its derivatives and structural analogues are an extensive group of aryl-tetralin-lignans of interest in pharmacology due to their promising anticancer and antitumor activity. The synthesis methods that have been proposed to date seek to resolve synthetic, stereochemical, pharmacodynamic and environmental aspects. In this review we have updated and brought together different classifications of lignan and podophyllotoxin synthesis. Transformation methods focus on the strategies used to form or functionalize rings A, B, C and D, as well as the configuration of the system of four stereogenic centers that fuse rings C and D. Подофілотоксин, його похідні та структурні аналоги є великою групою арилтетралінових лігнанів, що становлять інтерес для фармакології, зокрема завдяки їхній багатонадійній протипухлинній дії. Методи синтезу, запропоновані сьогодні, спрямовані на вирішення синтетичних, стереохімічних, фармакодинамічних та екологічних аспектів. У цьому огляді ми оновили й об’єднали різні класифікації синтезу подофілотоксину та споріднених сполук. Обговорені методи зосереджені на стратегіях формування або функціоналізації кілець A, B, C і D, а також на конфігурації чотирьох стереогенних центрів, які поєднують кільця C і D. National University of Pharmacy 2024-11-08 Article Article application/pdf https://ophcj.nuph.edu.ua/article/view/308942 10.24959/ophcj.24.308942 Journal of Organic and Pharmaceutical Chemistry; Vol. 22 No. 2 (2024); 3-25 Журнал органической и фармацевтической химии; Том 22 № 2 (2024); 3-25 Журнал органічної та фармацевтичної хімії; Том 22 № 2 (2024); 3-25 2518-1548 2308-8303 en https://ophcj.nuph.edu.ua/article/view/308942/304825 Copyright (c) 2024 Francisco Flores-Hernández, Tania Isabel Zárate-López, Marco Antonio Alcaráz-Cano, Jaime Escalante, José Domingo Rivera-Ramírez http://creativecommons.org/licenses/by/4.0
spellingShingle лігнани
подофілотоксин
арилтетралінові лігнани
етопозид
теніпозид
Flores-Hernández, Francisco
Zárate-López, Tania Isabel
Alcaráz-Cano, Marco Antonio
Escalante, Jaime
Rivera-Ramírez, José Domingo
Подофілотоксин та арилтетралінові лігнани: методи синтезу кілець A, B, C, D
title Подофілотоксин та арилтетралінові лігнани: методи синтезу кілець A, B, C, D
title_alt Podophyllotoxin and Aryltetralin Lignans: Methods for the Synthesis of Rings A, B, C, D
title_full Подофілотоксин та арилтетралінові лігнани: методи синтезу кілець A, B, C, D
title_fullStr Подофілотоксин та арилтетралінові лігнани: методи синтезу кілець A, B, C, D
title_full_unstemmed Подофілотоксин та арилтетралінові лігнани: методи синтезу кілець A, B, C, D
title_short Подофілотоксин та арилтетралінові лігнани: методи синтезу кілець A, B, C, D
title_sort подофілотоксин та арилтетралінові лігнани: методи синтезу кілець a, b, c, d
topic лігнани
подофілотоксин
арилтетралінові лігнани
етопозид
теніпозид
topic_facet lignans
podophyllotoxin
aryltetralin-lignans
etoposide
teniposide
лігнани
подофілотоксин
арилтетралінові лігнани
етопозид
теніпозид
url https://ophcj.nuph.edu.ua/article/view/308942
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