Хіральне розділення похідних β-СF3-α-проліну
An operationally simple and scalable preparation of all four stereoisomers of N-Boc β-CF₃-α-proline in high enantiomeric purity is described. Acylation of racemic cis-β-CF₃-α-proline with (S)-2-phenylpropanoic acid under standard amide coupling conditions affords a pair of diastereomeric amides that...
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V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the National Academy of Sciences of Ukraine
2025
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Ukrainica Bioorganica Acta| _version_ | 1869381603108585472 |
|---|---|
| author | Redka, Mykhailo O. Liashuk, Oleksandr S. Kondratov, Ivan S. Grygorenko, Oleksandr O. |
| author_facet | Redka, Mykhailo O. Liashuk, Oleksandr S. Kondratov, Ivan S. Grygorenko, Oleksandr O. |
| author_institution_txt_mv | [
{
"author": "Mykhailo O. Redka",
"institution": "V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the NAS of Ukraine, Kyiv, Ukraine; Enamine Ltd., Kyiv, Ukraine"
},
{
"author": "Oleksandr S. Liashuk",
"institution": "Taras Shevchenko National University of Kyiv, Kyiv, Ukraine; Enamine Scientific Research Institute (SRI), Kyiv, Ukraine"
},
{
"author": "Ivan S. Kondratov",
"institution": "V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the NAS of Ukraine, Kyiv, Ukraine; Enamine Germany GmbH, Frankfurt am Main, Germany "
},
{
"author": "Oleksandr O. Grygorenko",
"institution": "Taras Shevchenko National University of Kyiv, Kyiv, Ukraine; Enamine Ltd., Kyiv, Ukraine; Enamine Scientific Research Institute (SRI), Kyiv, Ukraine"
}
] |
| author_sort | Redka, Mykhailo O. |
| baseUrl_str | https://bioorganica.com.ua/index.php/journal/oai |
| collection | OJS |
| datestamp_date | 2026-06-29T16:03:06Z |
| description | An operationally simple and scalable preparation of all four stereoisomers of N-Boc β-CF₃-α-proline in high enantiomeric purity is described. Acylation of racemic cis-β-CF₃-α-proline with (S)-2-phenylpropanoic acid under standard amide coupling conditions affords a pair of diastereomeric amides that can be resolved by normal-phase column chromatography on multi-gram scale (up to 37 g per isomer). Subsequent acidic cleavage of the N,C-protection groups induce complete epimerization at the amino acid center; N-Boc protection of the resulting mixture followed by chromatographic separation provides individual N-Boc β-CF₃-α-proline stereoisomers with ee > 95%. The same sequence applied to both diastereomeric intermediate N-acyl derivatives furnishes the full set of four N-Boc β-CF₃-α-prolines in only three synthetic steps, without the need for chiral chromatography. This robust resolution protocol transforms β-CF₃-α-proline ester into a easily accessible chiral building block for peptide synthesis, conformational studies and medicinal chemistry applications. |
| doi_str_mv | 10.15407/bioorganica2025.02.035 |
| first_indexed | 2026-02-08T07:59:48Z |
| format | Article |
| fulltext |
ISSN 1814-9758. Ukr. Bioorg. Acta, 2025, Vol. 20, N 2
UDC 577.112.34
DOI: https://doi.org/10.15407/bioorganica2025.02.035
35
RESEARCH ARTICLE
Practical сhiral separation of β-СF3-α-proline
Mykhailo O. Redka1,3, Oleksandr S. Liashuk,2,4* Ivan S. Kondratov,1,5 Oleksandr O. Grygorenko.2,3,4
1 V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the NAS of Ukraine, Kyiv, Ukraine
2 Taras Shevchenko National University of Kyiv, Kyiv, Ukraine
3 Enamine Ltd. (www.enamine.net), Kyiv, Ukraine
4 Enamine Scientific Research Institute (ESRI), Kyiv, Ukraine
5 Enamine Germany GmbH, Frankfurt am Main, Germany
Abstract: An operationally simple and scalable preparation of all four stereoisomers of N-Boc β-CF₃-α-proline in high enantiomeric purity
is described. Acylation of racemic cis-β-CF₃-α-proline with (S)-2-phenylpropanoic acid under standard amide coupling conditions affords
a pair of diastereomeric amides that can be resolved by normal-phase column chromatography on multi-gram scale (up to 37 g per isomer).
Subsequent acidic cleavage of the N,C-protection groups induce complete epimerization at the amino acid center; N-Boc protection of the
resulting mixture followed by chromatographic separation provides individual N-Boc β-CF₃-α-proline stereoisomers with ee >95%. The
same sequence applied to both diastereomeric intermediate N-acyl derivatives furnishes the full set of four N-Boc β-CF₃-α-prolines in only
three synthetic steps, without the need for chiral chromatography. This robust resolution protocol transforms β-CF₃-α-proline ester into a
easily accessible chiral building block for peptide synthesis, conformational studies and medicinal chemistry applications.
Keywords: fluorine; proline; enantiomeric separation; fluorinated building blocks.
Introduction
Proline occupies a unique position among proteinogenic
amino acids due to its cyclic structure and secondary amine
functionality, which strongly restrict the accessible
backbone dihedral angles and modulate cis/trans amide
equilibria [1, 2]. As a consequence, proline residues play a
central role in controlling local and global peptide
conformation, stabilizing β-turns and shaping the three-
dimensional structures of proteins and peptidomimetics [3-
6]. Edited proline motifs have gained/recieved increasing
attention due to their potential for fine tuning of structural
and physicochemical properties [7]. Among others,
introduction of fluorine-containing groups can profoundly
affect acidity/basicity, lipophilicity, conformation, and
metabolic stability without dramatically altering the overall
Received:
Revised:
Accepted:
Published online:
23.09.2025
06.10.2025
28.10.2025
30.12.2025
Corresponding author. Tel.: +380-66-728-1226;
e-mail: o.s.liashuk@gmail.com (O.S. Liashuk)
ORCID: 0000-0002-2677-435X
size of a fragment [8-12]. Fluorinated prolines metabolic
stability without dramatically altering the overall size of a
fragment [8-12]. As a result, fluorinated prolines have
found real-world applications [13]. Being a part of
commercial drugs Ibuzatrelvir (PF-07817883), a second-
generation, orally bioavailable, is SARS-CoV-2 main pro-
tease (Mpro and 3CLpro) inhibitor [14], or Danicopan, a first-
in-class oral factor D (FD) inhibitor (Figure 1, A) [15].
Among agrochemicals, Profluazol (a herbicidal inhibitor of
protoporphyrinogen oxidase (PPO)) exemplifies the
relevance of fluorinated proline derivatives in crop
protection [16].
β-CF₃-α-proline derivatives repeatedly appeared in
literature as a potential NMR probes with acceptable
lipophilicity profile [17] and diastereomerically-dependent
metabolic stability [18, 19]. Currently reported approaches
to β-CF₃-α-prolines allowed access to either cis- or trans-
isomeric compounds as racemic mixtures (Figure 1, B)
[18, 20]. To date, enantiomers separation was successfully
achieved through chromatographic resolution of C-terminal
modified β-CF₃-α-prolines [18, 19]. However, due to the
high proteolytic stability of amide derivatives of cis-β-CF₃-
α-proline, isolation of enantiomerically pure free
cis-amino acids remains a challenging task [18, 19].
© Redka M.O. et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use,
distribution, and reproduction in any medium, provided the original author and source are credited.
Ukrainica Bioorganica Acta
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https://orcid.org/0000-0002-2677-435X
ISSN 1814-9758. Ukr. Bioorg. Acta, 2025, Vol. 20, N 2
36
Herein, we report an operationally simple and scalable
method that resolves racemic cis-β-CF₃-α-proline (±)-cis-1
into its individual enantiomers via N-modification strategy
(Figure 1, C). The protocol affords all 4 stereoisomeric
forms of N-Boc cis-β-CF₃-α-proline 2 in high enantiomeric
excess and is suitable for multi-gram preparation, thus
providing sufficient material quantities for peptide
synthesis, conformational and physicochemical studies, and
biological evaluation.
N
O
N
O
HN S
O
O Cl
Cl
F
F
Profluazol
N
N
O Br
F
Danicopan
N
O
H
N
N
N
NO
O
N
CF3
HN O
O
N
O
HN
H
N
O
Ibuzatrelvir
a SARS-CoV-2
main protease (Mpro)
inhibitor
factor D
inhibitor
protoporphyrinogen
oxidase (PPO) inhibitor
(B) Reported data on the synthesis of ß-?F3-a-Proline
(C) This
work
(A) Fluorinated Pro-drugs
N
H
CF3
O
O
N
Boc
CF3
OH
O
Tolmachova et al., 2018
RF
CHO
N
HEtO2C
O
O
N
Boc
CO2Et
RF
< 0.5 gN
H
CO2H
RF
5–7 steps1. Hydrogenation
2. FG
transformations
cis- and trans-
4 enantiomers
f
rom single batch
Decagram
s
cale
1. N-derivatization
2
Redka et al., 2025
high dr,
racemates
RF = CHF2, CF3
2. CC separation
3. PG conversion
*
*
N
Boc
CF3
H
N
O
Ph
X
N
Boc
CF3
OH
O
N
Boc
CF3
OH
O
X = H or OH
Modification
Separation
Hydrolysis Hydrolysis
Separation
and (2S, 3R)-enantiomer
unsuccesful
(±)-c
is-1
Figure 1. (A) Fluorinated proline motifs in drugs; (B) Synthesis
and enantiomer separation reported in literature; (C) Results,
reported in this work.
Results and Discussion
As was mentioned in introduction, previously reported
attempts to obtain enantiomerically pure β-CF₃-α-prolines
(either cis- or trans-) were based on the separation of the
C-modified amide derivatives.
Although the separation of the C-derivatives was
successful, subsequent deprotection of the carboxamide
fragment in the cis-isomeric β-CF₃-α-proline derivatives
required prolonged reaction time under harsch conditions
and led to significant epimerization at the the α-position.
Due to this the corresponding enantiomers of cis-2 were
accessed only through additional chromatographic
purification on chiral stationary phase, being impractical for
large scale preparation of the target compounds.
To avoid the carboxamide hydrolysis step, we envisaged
an alternative approach, based on the N-derivatization
strategy [21, 22]. Treatment of the starting amine (±)-cis-1
with (S)-3 under classical amide coupling conditions
(HATU, DIPEA, DMF, rt, 12 h) cleanly produced corres-
ponding amide cis-4, which was successfully separated to
diastereomeric pairs (+)-cis-4 and (−)-cis-4, yielding up to
37 g of each of the isomers (Scheme 1). Initially, the
absolute configuration of the stereocentres in the separated
compounds were unknown, therefore each of the com-
pounds were identified by their rotational angle and
retention time on the chromatograms of the HPLC with
chiral stationary phase and assigned (−)-cis-4 and (+)-cis-4
according to the lower and higher [α]D value, respectively.
Upon further studies the exact configuration of the centres
were established for both (+)-cis-4 and (−)-cis-4; accurate
representation of the stereocenters on Scheme 1 and below
were made for clarity.
N
H
CF3
O
O
N
CF3
O
O
O
O
OH
N
CF3
O
O
O
(S)-3
+
(-)-cis-4 (+)-cis-4
37 g 37 g
*absolute configurations were established after subsequent steps
HATU, DIPEA
DMF
[a]D = 68.1° [a]D = 80.8°
(±)-cis-1
de > 99% de > 99%
50%
HCl
Scheme 1. Synthesis and separation of the amide derivatives 4.
N
CF3
O
O
O
Ph (-)-cis-4
N+
CF3
OH
O
N+
CF3
OH
O
+
Boc2O
MeOH N
Boc
CF3
OH
O
N
Boc
CF3
OH
O
(2S,3R)-2 (2R,3R)-2
(-)-cis-5 (-)-trans-5
analyzed
by 19F NMR
Crude
mixture
of
cis-/trans-5
Chromatography
separation and
Et3N
N
Boc
CF3
OH
O
(2S,3R)-2
N
Boc
CF3
OH
O
(2R,3R)-2
N
Boc
CF3
OH
O
N
Boc
CF3
OH
O
(2S,3S)-2 (2R,3S)-2
5M HCl
dioxane/H2O
1:1 v/v
ca. 1:1
[a]D = 20.1°
ee > 99%
9.3. g
[a]D = -20.4°
ee > 99%
30% from
(+)-cis-5
7.7 g
[a]D = 27.0°
ee > 95%
7.2 g
ee > 97%
[a]D = -30.3°
repeated for (+)-isomer Rf = 0.50 Rf = 0.10
36% from
(-)-cis-5
28% from
(-)-trans-5
HH HH
Cl
-
Cl
-
6.4 g
25% from
(+)-cis-5
(A)
(B)
(C)
reflux
Scheme 2. (A) Deprotection of compound (−)-cis-4. (B) Prepa-
ration and separation of N-Boc β-CF₃-α-proline 2. (C) Compo-
unds, prepared in this work.
M.O. Redka et al.
37
Further studies were devoted to the deprotection of
compounds 4 aiming the preparation of the convenient in
routine application building blocks. Alkaline hydrolysis was
again found inefficient, giving moderate 72 h-conversion to
unprotected compounds 5 even at elevated temperatures
(less than 40%). In opposite, acidic cleavage of the
N,C-protection groups was found to be more advantageous
– upon reflux in 5M HCl in dioxane/water mixture
complete conversion to 5 could be achieved in 72 h without
significant decomposition of the material (Scheme 2, A).
Albeit high isolated yield of the products 5, complete
epimerization at the α-centre of (−)-cis-4 occurred
producing ca. 1:1 mixture of (−)-cis-5 and (−)-trans-5
(concluded by 19F NMR of the reaction mixture). Any
attempts to improve the quality of the product (including
variation of the concentration and temperature) were
unfruitful; changing of the acid (i.e. TFA or H2SO4)
typically led to diminishment of the yield or were unable to
cleave the amide fragment.
To achieve the separation of the diastereomeric mixture,
the obtained crude mixture of (−)-cis-5 and (−)-trans-5 was
subjected for N-Boc protection under typical conditions
(Boc2O, Et3N in MeOH) and subsequent separation by flash
column chromatography using Hex/THF gradient (from 3:1
to 1:1 v/v). Analysis of the two obtained compounds and
comparison thereof with previously reported data approved
the high enantiomeric purity (ee > 99%) and allowed exact
assignment of the stereocenters in compounds (−)-cis-2 and
(−)-trans-2, found to be (R)- at β-position (Scheme 2, B)
[18,19]. The same procedure, applied for (+)-cis-4 granted
access to compounds (+)-cis-2 and (+)-trans-2 with (S)-con-
figuration at β-position in comparable yields. Altogether, a
full set of enantiomers of N-Boc β-CF₃-α-proline 2 was
obtained in 3 synthetic steps without application of chiral
separation techniques (Scheme 2, C).
Conclusions
In summary, we have developed an operationally simple
and scalable strategy for the preparation of enantiomerically
pure β-CF₃-α-prolines based on the separation and
transformations of the N-acyl derivatives of the known
scaffold. Acylation of the racemic cis-β-CF₃-α-proline with
(S)-2-phenylpropanoic acid under standard amide bond
formation conditions provided diastereomeric amides
suitable for separation via normal phase column
chromatography on multi-gram scale (up to 37 g for each
isomer). Subsequent acidic cleavage of the N,C-protection
groups led to a complete epimerization of the amino acid
fragment. Subsequent N-Boc protection and separation via
column chromatography allowed the separate isolation of
the diastereomeric pair of N-Boc amino acids. Comparison
of the analytical data of the obtained compounds with
literature data confirmed their high enantiomeric purity (ee
> 95%) and allowed unambiguous assignment of the
stereocentres absolute configuration. Application of the
same protocol to both diastereomeric amides furnished the
full set of four stereoisomers of N-Boc β-CF₃-α-proline in
only three synthetic steps, without the need for chiral
chromatographic resolution at any stage.
Experimental section
The solvents were purified according to the standard
procedure [23]. Ester (±)-cis-1⸱HCl was synthesized
according to the previously reported procedure [20]. All
other reagents were obtained from Enamine Ltd. Melting
points were measured on the MPA100 OptiMelt automated
melting point system. 1H, 13C{1H}, and 19F{1H} NMR
spectra were recorded on a Bruker 170 Avance 500
spectrometer (at 500 MHz for 1H NMR) or Varian Unity
Plus 400 spectrometer (at 400 MHz for 1H NMR, 101 MHz
for 13C{1H} NMR, and 376 MHz for 19F{1H} NMR). NMR
chemical shifts are reported in ppm (δ scale) downfield
from TMS as an internal standard and are referenced using
residual NMR solvent peaks at 7.26 and 77.16 ppm for
1H and 13C{1H} in CDCl3, 2.50 and 39.52 ppm for 1H and
13C{1H} in DMSO-d6. Coupling constants (J) are given in
Hz. Spectra are reported as follows: chemical shift (δ, ppm),
multiplicity, integration, and coupling constants (Hz).
Elemental analyses were performed at the Laboratory of
Organic Analysis, Department of Chemistry, Taras
Shevchenko National University of Kyiv. Preparative flash
chromatography was performed on a puriFlash® XS_520
Plus using Interchim PF-100P6-F0800 column. Chiral
HPLC analysis for (−)-cis-4 and (+)-cis-4 was conducted
using Chiralpak ID (250×4.6 mm, 5 μm); Chiralpak IB
(250×4.6 mm, 5 μm); Chiralpak IA-U (100×3.0 mm,
1.6 μm); Chiralpak IG-U (100×3.0 mm, 1.6 μm) and
Chiralcel OJ-H (250×4.6 mm, 5 μm) columns. Chiral HPLC
analysis for a set of compounds 2 was conducted using
Chiralpak IC (250 × 4.6 mm, 5 µm).
General procedure for the synthesis of compounds (±)-cis-
4.
To a solution of ester (±)-cis-1⸱HCl [18, 19]. (110.0 g,
0.444 mol) in DMF (500 ml), (S)-2-phenylpropanoic acid
(70.1 g, 0.467 mol), then N,N-diisopropylethylamine
(154.9 ml, 114.9 g, 0.889 mol) and HATU (219.6 g,
0.578 mol) were subsequently added at room temperature
and the resulting mixture was stirred at the same
temperature for 16 h and then concentrated under reduced
pressure to dryness. The residue was purified by flash
column chromatography (hexanes/t-BuOMe 2:3 to 4:1 v/v)
with separation of two diastereoisomers. Diastereomeric
purity was assigned by NMR and HPLC on chiral stationary
phase (see SI for details).
Ethyl (2S,3R)-1-[(2S)-2-phenylpropanoyl]-3-(trifluorome-
thyl)pyrrolidine-2-carboxylate ((-)-cis-4)).
Yield: 37.3 g, 0.109 mol, 25%. Yellowish viscous oil;
TLC (hexane/t-BuOMe 1:1 v/v) Rf 0.33; [α]D
20 68.1 (c 1.00,
MeOH); 1H NMR (500 MHz, CDCl3) δ 7.37-7.29 (m, 2H),
7.28-7.21 (m, 3H, overlapped with solvent residual peak),
4.76 (d, J = 8.2 Hz, 1H), 4.21-4.11 (m, 2H), 3.71 (q, J =
7.0 Hz, 1H), 3.57-3.47 (m, 2H), 3.08-2.97 (m, 1H), 2.27-
ISSN 1814-9758. Ukr. Bioorg. Acta, 2025, Vol. 20, N 2
38
2.06 (m, 2H), 1.42 (d, J = 7.0 Hz, 3H), 1.22 (t, J = 7.2 Hz,
3H).; 13C NMR (101 MHz, CDCl3) δ 172.6, 168.9, 140.5,
129.0, 127.6, 127.1, 125.1 (q, JC-F = 277.4 Hz), 61.7, 58.3,
45.5, 45.09, 45.08 (q, JC-F = 30.0 Hz), 44.6, 24.7, 20.4, 13.9;
19F NMR (376 MHz, CDCl3) δ -68.05; Anal. Calcd. for
C17H20F3NO3: C, 59.47; H, 5.87; N, 4.08. Found: C, 60.36;
H, 5.57; N, 4.54.
Ethyl (2R,3S)-1-[(2S)-2-phenylpropanoyl]-3-(trifluorome-
thyl)pyrrolidine-2-carboxylate (+)-cis-4).
Yield: 37.1 g, 0,108 mol, 24%. Yellowish viscous oil;
TLC (hexane/EtOAc 1:1 v/v) Rf 0.44; [α]D
20
80.8 (c 1.00,
MeOH); 1H NMR (500 MHz, CDCl3) δ 7.36-7.18 (m, 5H,
overlapped with solvent residual peak), 4.69 (d, J = 8.0 Hz,
1H), 4.21 (q, J = 7.1 Hz, 2H), 3.91 (t, J = 9.4 Hz, 1H), 3.78
(q, J = 6.9 Hz, 1H), 3.24-3.15 (m, 1H), 2.95-2.83 (m, 1H),
2.40-2.28 (m, 1H), 2.15-2.04 (m, 1H), 1.43 (d, J = 6.9 Hz,
3H), 1.28 (t, J = 7.1 Hz, 3H).); 13C NMR (101 MHz,
CDCl3) δ 172.9, 169.5, 140.9, 129.0, 127.6, 127.2, 125.0 (q,
JC-F = 277.4 Hz), 61.8, 58.3, 45.4, 45.1 (q, JC-F = 30.0 Hz),
44.8, 24.5, 20.0, 13.9; 19F NMR (376 MHz, CDCl3) δ
-68.12; Anal. Calcd. for C17H20F3NO3: C, 59.47; H, 5.87; N,
4.08. Found 601.2144.
General procedure for the synthesis of compounds 2.
To a solution of compound 4 (37.3 g, 0.109 mol) in
anhydrous HCl (ca. 4 M in dioxane, 125 ml), 6 M aq HCl
(125 ml) was added in one portion. The resulting mixture
was heated to 100 °C and stirred at this temperature for
72 h. Upon completion of the reaction (concluded by 1H
NMR spectrum of the small aliquot of the reaction mixture),
organic solvents were removed under reduced pressure and
the aqueous residue was extracted with t-BuOMe
(3 × 50 ml). The organic phase was discarded, the aqueous
layer was evaporated to dryness under reduced pressure,
giving a mixture of cis-/trans-5 (in a ca. 1:1 ratio) as HCl
salts, which was used in the next step without further
purification. To a solution of crude cis-/trans-5⸱HCl
(20.0 g, ca. 0.091 mol) in MeOH (300 ml), Et3N (38.2 ml,
27.7 g, 0.274 mol) and neat Boc2O (26.2 g, 0.120 mol) were
subsequently added in a dropwise manner at room
temperature. The resulting mixture was stirred at the same
temperature until the gas evolution ceased and concentrated
under reduced pressure. The residue was dissolved in water
(100 ml), the resulting solution was acidified with 1 M aq
NaHSO4 (170 ml) to pH = 4 and then extracted with EtOAc
(3 × 150 ml). The combined organic layers were dried over
Na2SO4 and concentrated under reduced pressure to give
crude product as a mixture of disatereoisomers. Individual
isomers were separated by column chromatography
(hexanes/THF 3:1 to 1:1, v/v gradient).
(2S,3R)-1-(tert-Butoxycarbonyl)-3-(trifluoromethyl)pyrro-
lidine-2-carboxylic acid ((2S,3R)-2).
Yield: 9.31 g, 32.9 mmol, 36 % (from 20.0 g, 91.1 mmol
of (−)-cis-5). Colourless powder, mp 126-127 °C; TLC
(hexanes/THF 2:1 v/v) Rf 0.49; [α]D
20 20.15 (c 0.50,
MeOH); enantiomeric excess (> 99 %) was determined by
chiral HPLC: 100:0 er, tR (S,R)-major enantiomer, 9.6 min
(Chiralpack IC column; 10% 2-propanol in hexane (0.1 %
TFA); 0.6 mL/min). Other physical and spectral data are
consistent with those previously reported [19].
(2R,3R)-1-(tert-Butoxycarbonyl)-3-(trifluoromethyl)pyrro-
lidine-2-carboxylic acid ((2R,3R)-2).
Yield: 7.24 g, 25.6 mmol, 28 % (from 20.0 g, 91.1 mmol
of (−)-cis-5). Colourless crystals, mp 86-87 °C; TLC
(hexanes/THF 2:1 v/v) Rf = 0.11; [α]D
20 26.97 (c 0.50,
MeOH); enantiomeric excess (˃ 95 %) was determined by
chiral HPLC: 98.1:1.9 er, tR (R,R)-major enantiomer, 6.2
min (Chiralpack IC column; 10% 2-propanol in hexane
(0.1 % TFA); 0.8 mL/min). Other physical and spectral data
are consistent with those previously reported [19].
(2R,3S)-1-(tert-Butoxycarbonyl)-3-(trifluoromethyl)pyrro-
lidine-2-carboxylic acid ((2R,3S)-2).
Yield: 7.67 g, 27.1 mmol, 30 % (from 19.9 g, 91.0 mmol
of (+)-cis-5). Colourless powder; mp 127-129 °C; TLC
(hexane/THF 2:1 v/v) Rf 0.48; [α]D
20 -20.38 (c 0.50,
MeOH); enantiomeric excess (˃ 99 %) was determined by
chiral HPLC: 100:0 er, tR (R,S)-major enantiomer, 10.1 min
(Chiralpack IC column; 10% 2-propanol in hexane (0.1%
TFA); 0.6 mL/min). Other physical and spectral data are
consistent with those previously reported [19].
(2S,3S)-1-(tert-Butoxycarbonyl)-3-(trifluoromethyl)-pyrro-
lidine-2-carboxylic acid ((2S,3S)-2).
Yield: 6.44 g, 22.7 mmol, 25% (from 19.9 g, 91.0 mmol
of (+)-cis-5)). Beige powder; mp 84-85 °C; TLC
(hexanes/THF 2:1 v/v) Rf 0.14; [α]D
20 -30.32 (c 0.50,
MeOH); enantiomeric excess (˃ 97%) was determined by
chiral HPLC: 98.6:1.4 er, tR (S,S)-major enantiomer, 9.7
min (Chiralpack IC column; 5% 2-propanol in hexane
(0.1% TFA); 0.6 mL/min). Other physical and spectral data
are consistent with those previously reported [19].
Notes
Acknowledgments and finances. This work was funded
by Enamine Ltd. O.S.L. received additional funding from
Ministry of Education and science of Ukraine, grant
No. 25BF037-01 (0125U002249). The authors thank
Dr. Anastasiia Hurieva for help with manuscript
preparation. We also thank Prof. Andriy A. Tolmachov for
his encouragement and support, and all the people of
Ukraine for making this manuscript possible.
Data availability statement. The raw NMR data is
freely available at public repository (DOI:
https://doi.org/10.5281/zenodo.17817173 ).
Conflict of interest. The authors are/have been
employees, trainees, or consulting scientists of Enamine
https://doi.org/10.5281/zenodo.17817173
M.O. Redka et al.
39
Ltd. that offers all the building blocks described in this
paper in the company’s catalog.
Supporting information
The Supporting Information to this article contains the
copies of NMR spectra of the novel compounds and chiral
analysis data for compounds 4.
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Хіральне розділення похідних β-СF3-α-проліну
М.O. Редька1,3, О.C. Ляшук2,4*, І.C. Кондратов1,5, О.O. Григоренко2,3,4.
1 Інститут біоорганічної хімії та нафтохімії ім. В.П. Кухаря НАН України, Київ, Україна
2 Київський національний університет імені Тараса Шевченка, Київ, Україна
3 ТОВ «Єнамін» (www.enamine.net), Київ, Україна
4 Науково-дослідний інститут (НДІ) «Єнамін», Київ, Україна
5 ТОВ «Єнамін-Німеччина» (GmbH), Франкфурт-на-Майні, Німеччина
Резюме: У цій роботі описано просту та масштабовану стратегію отримання всіx чотирьох стереоізомерів N-Boc β-CF₃-α-проліну з високою
енантіомерною чистотою. Ацилювання рацемічного цис-β-CF₃-α-проліну (S)-2-фенілпропановою кислотою за стандартних умов амідного
каплінгу приводить до утворення пари діастереомерних амідів, які можна розділити за допомогою нормально-фазової колонкової хроматографії в
багатограмовому масштабі (до 37 г на кожен ізомер). Подальше кислотне розщеплення N- і C-термінальних захисних груп приводило до повної
епімеризації в амінокислотному центрі; подальша обробка отриманої суміші амінокислот Boc2O з хроматографічним розділенням продуктів дає
окремі діастереомери N-Boc β-CF₃-α-проліну з ee > 95%. Застосування цієї послідовності до обох діастереомерних проміжних N-ацильних
похідних забезпечує доступ до повного набору з чотирьох ізомерних N-Boc β-CF₃-α-пролінів лише за три синтетичні етапи, без використання
хіральної хроматографії. Запропонований надійний протокол розділення перетворює β-CF₃-α-пролін на практично доступний хіральний
будівельний блок для синтезу пептидів, конформаційних досліджень та застосувань у медичній хімії.
Ключові слова: флуор; пролін; енантіомерне розділення; флуоровані будівельні блоки.
|
| id | oai:ojs2.bioorganica.com.ua:article-118 |
| institution | Ukrainica Bioorganica Acta |
| keywords_txt_mv | keywords |
| language | English |
| last_indexed | 2026-06-30T01:00:22Z |
| publishDate | 2025 |
| publisher | V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the National Academy of Sciences of Ukraine |
| record_format | ojs |
| resource_txt_mv | bioorganicacomua/8a/728884fc5788c4557ad9fa4efe038f8a.pdf |
| spelling | oai:ojs2.bioorganica.com.ua:article-1182026-06-29T16:03:06Z Practical сhiral separation of β-СF3-α-proline Хіральне розділення похідних β-СF3-α-проліну Redka, Mykhailo O. Liashuk, Oleksandr S. Kondratov, Ivan S. Grygorenko, Oleksandr O. fluorine proline enantiomeric separation fluorinated building blocks флуор пролін енантіомерне розділення флуоровані будівельні блоки An operationally simple and scalable preparation of all four stereoisomers of N-Boc β-CF₃-α-proline in high enantiomeric purity is described. Acylation of racemic cis-β-CF₃-α-proline with (S)-2-phenylpropanoic acid under standard amide coupling conditions affords a pair of diastereomeric amides that can be resolved by normal-phase column chromatography on multi-gram scale (up to 37 g per isomer). Subsequent acidic cleavage of the N,C-protection groups induce complete epimerization at the amino acid center; N-Boc protection of the resulting mixture followed by chromatographic separation provides individual N-Boc β-CF₃-α-proline stereoisomers with ee &gt; 95%. The same sequence applied to both diastereomeric intermediate N-acyl derivatives furnishes the full set of four N-Boc β-CF₃-α-prolines in only three synthetic steps, without the need for chiral chromatography. This robust resolution protocol transforms β-CF₃-α-proline ester into a easily accessible chiral building block for peptide synthesis, conformational studies and medicinal chemistry applications. У цій роботі описано просту та масштабовану стратегію отримання всіч чотирьох стереоізомерів N-Boc β-CF₃-α-проліну з високою енантіомерною чистотою. Ацилювання рацемічного цис-β-CF₃-α-проліну (S)-2-фенілпропановою кислотою за стандартних умов амідного каплінгу приводить до утворення пари діастереомерних амідів, які можна розділити за допомогою нормально-фазової колонкової хроматографії в багатограмовому масштабі (до 37 г на кожен ізомер). Подальше кислотне розщеплення N- і C-термінальних захисних груп призводило до повної епімеризації в амінокислотному центрі; подальша обробка отриманої суміші амінокислот Boc2O з хроматографічним розділенням продуктів дає окремі діастереомери N-Boc β-CF₃-α-проліну з ee &gt; 95%. Застосування цієї послідовності до обох діастереомерних проміжних N-ацильних похідних забезпечує доступ до повного набору з чотирьох ізомерних N-Boc β-CF₃-α-пролінів лише за три синтетичні етапи, без використання хіральної хроматографії. Запропонований надійний протокол розділення перетворює β-CF₃-α-пролін на практично доступний хіральний будівельний блок для синтезу пептидів, конформаційних досліджень та застосувань у медичній хімії. V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the National Academy of Sciences of Ukraine 2025-12-31 Article Article application/pdf application/pdf https://bioorganica.com.ua/index.php/journal/article/view/118 10.15407/bioorganica2025.02.035 Ukrainica Bioorganica Acta; Vol. 20 No. 2 (2025): Ukrainica Bioorganica Acta; 35-39 Ukrainica Bioorganica Acta; Том 20 № 2 (2025): Ukrainica Bioorganica Acta; 35-39 1814-9766 1814-9758 10.15407/bioorganica2025.02 en https://bioorganica.com.ua/index.php/journal/article/view/118/104 https://bioorganica.com.ua/index.php/journal/article/view/118/105 Copyright (c) 2025 Mykhailo O. Redka, Oleksandr S. Liashuk, Ivan S. Kondratov, Oleksandr O. Grygorenko https://creativecommons.org/licenses/by/4.0 |
| spellingShingle | флуор пролін енантіомерне розділення флуоровані будівельні блоки Redka, Mykhailo O. Liashuk, Oleksandr S. Kondratov, Ivan S. Grygorenko, Oleksandr O. Хіральне розділення похідних β-СF3-α-проліну |
| title | Хіральне розділення похідних β-СF3-α-проліну |
| title_alt | Practical сhiral separation of β-СF3-α-proline |
| title_full | Хіральне розділення похідних β-СF3-α-проліну |
| title_fullStr | Хіральне розділення похідних β-СF3-α-проліну |
| title_full_unstemmed | Хіральне розділення похідних β-СF3-α-проліну |
| title_short | Хіральне розділення похідних β-СF3-α-проліну |
| title_sort | хіральне розділення похідних β-сf3-α-проліну |
| topic | флуор пролін енантіомерне розділення флуоровані будівельні блоки |
| topic_facet | fluorine proline enantiomeric separation fluorinated building blocks флуор пролін енантіомерне розділення флуоровані будівельні блоки |
| url | https://bioorganica.com.ua/index.php/journal/article/view/118 |
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