Candida antarctica lipase-catalyzed doubly enantioselective aminolysis reactions. Chemoenzymatic synthesis of 3-hydroxypyrrolidines and 4-(silyloxy)-2-oxopyrrolidines with two stereogenic centers

Article abstract of DOI:10.1021/jo981630a

Aminolyses of racemic and prochiral 3-hydroxyesters with racemic amines are effectively catalyzed by Candida antarctica lipase. In these processes, the simultaneous resolution of the ester and the amine, or the corresponding asymmetrization-resolution, takes place. In all cases, the high enantioselectivity shown by the lipase toward all the reactants allows the preparation of enantiopure 3-hydroxyamides with very high diastereomeric ratios. These 3-hydroxyamides are used as starting materials in the synthesis of 3-hydroxy-and 2-oxopyrrolidines, both containing two stereogenic centers in their structures.

Full text of DOI:10.1021/jo981630a

1464
J . Org. Chem. 1999, 64, 1464-1470
Ca n d id a a n ta r ctica Lip a se-Ca ta lyzed Dou bly En a n tioselective
Am in olysis Rea ction s. Ch em oen zym a tic Syn th esis of
3-Hyd r oxyp yr r olid in es a n d 4-(Silyloxy)-2-oxop yr r olid in es w ith
Tw o Ster eogen ic Cen ter s
V´ıctor M. Sa´nchez, Francisca Rebolledo, and Vicente Gotor*
Departamento de Quı´mica Orga´nica e Inorga´nica, Universidad de Oviedo, E-33071, Oviedo, Spain
Received August 11, 1998
Aminolyses of racemic and prochiral 3-hydroxyesters with racemic amines are effectively catalyzed
by Candida antarctica lipase. In these processes, the simultaneous resolution of the ester and the
amine, or the corresponding asymmetrization-resolution, takes place. In all cases, the high
enantioselectivity shown by the lipase toward all the reactants allows the preparation of enantiopure
3-hydroxyamides with very high diastereomeric ratios. These 3-hydroxyamides are used as starting
materials in the synthesis of 3-hydroxy- and 2-oxopyrrolidines, both containing two stereogenic
centers in their structures.
In tr od u ction
difficulty in matching an appropriate pair of substrates.
In most cases the enantioselectivity of the enzyme toward
a given substrate, for example the acyl donor, is affected
by the structure of the acyl acceptor and vice versa.6 This
implies that, although high enantioselectivities are at-
tained in the simple kinetic resolution of the substrates,
no reliable prediction may be made about the outcome
of the double kinetic resolutions. Nevertheless, a good
criterion for selecting substrates for a doubly enantiose-
lective process may be that their simple resolutions are
efficient themselves.
Lipase-catalyzed kinetic resolution of racemates is a
well-established method for the preparation of enantio-
merically enriched products.1 In organic solvents, these
enzymes have been widely used to catalyze esterification,
transesterification, and aminolysis processes.2 Usually,
the reaction is carried out with a racemic or prochiral
nucleophile (alcohol or amine) and an achiral acyl donor
(acid or ester) or vice versa, achieving the kinetic resolu-
tion of the racemate. As the enantiorecognition of the
nucleophile and the acyl donor occur at different sites of
the lipase,3 both resolutions could take place in the same
reaction. These processes, named “doubly enantioselec-
tive”, are much less-documented than the simple kinetic
resolutions. The interest of these reactions is obvious,
because if the lipase shows a high enantioselectivity
toward both reagents, a product with both a high dia-
stereomeric ratio (dr) and a high enantiomeric excess (ee),
as well as the resolution of the nucleophile and the acyl
donor, could be reached in only one step.
Here we report some highly diastereo- as well as
enantioselective aminolysis reactions mediated by Can-
dida antarctica lipase (CAL B) using a racemic [(()-1]
and a prochiral (4) â-hydroxyester and racemic amines
[(()-2a -c] as substrates. Several reasons support the
selection of these substrates. First of all, lipase-catalyzed
aminolysis of esters is an irreversible reaction,7 which is
more convenient for a kinetic resolution process than
reversible reactions,8 namely esterification and transes-
terification. So far the CAL B (Novozym SP 435) has
proven to be the most effective catalyst for the aminolysis
reaction in organic solvents. Particularly, this enzyme
has shown a great efficiency to catalyze both the simple
kinetic resolution of racemic â-hydroxyesters9 and the
asymmetrization of dimethyl 3-hydroxyglutarate10 by
aminolysis reaction, as well as the enantioselective
acylation of racemic amines with a broad variety of
esters.11 We chose three different primary amines as
nucleophiles, bearing, respectively, a phenyl group, a
furyl ring, and a linear alkyl chain at the stereocenter.
Some examples of doubly enantioselective reactions
catalyzed by lipases have appeared in the literature but,
in most cases, the reactions proceeded with modest
diastereoselectivities,4 except in some interesterifications,
in which good diastereomeric ratios were achieved,
although at low percentage of conversion.5 The lack of a
good example of this kind of processes can be due to the
(1) (a) Faber, K. Biotransformations in Organic Chemistry.
A
Textbook, 2nd ed.; Springer-Verlag: New York, 1995. (b) Wong, C.-H.;
Whitesides, G. M. Enzymes in Synthetic Organic Chemistry; Tetrahe-
dron Organic Chemistry Series Vol. 12.; Baldwin, J . E., Ed.; Pergamon
Press: New York, 1994.
(2) Santaniello, E.; Ferraboschi, P.; Grisenti, P.; Manzocchi, A.
Chem. Rev. 1992, 92, 1071.
(5) Macfarlane, E. L. A.; Roberts, S. M.; Steukers, V. G. R.; Taylor,
P. L. J . Chem. Soc., Perkin Trans. 1 1993, 2287.
(6) (a) Ema, T.; Maeno, S.; Takaya, Y.; Sakai, T.; Utaka, M. J . Org.
Chem. 1996, 61, 8610. (b) Holmberg, E.; Hult, K. Biocatalysis 1992, 5,
289.
(7) (a) West, J . B.; Wong, C. H. Tetrahedron Lett. 1987, 28, 1629.
(b) Margolin, A. L.; Klibanov, A. M. J . Am. Chem. Soc. 1987, 109, 3802.
(8) Chen, C. S.; Sih, C. J . Angew. Chem., Int. Ed. Engl. 1989, 28,
695.
(3) (a) Grochulski, P.; Bouthillier, F.; Kazlauskas, R. J .; Serreqi, A.
N.; Schrag, J . D.; Ziomek, E.; Cygler, M. Biochemistry 1994, 33, 3494.
(b) Cygler, M.; Grochulski, P.; Kazlauskas, R. J .; Schrag, J . D.;
Bouthillier, F.; Rubin, B.; Serreqi, A. N.; Gupta, A. K. J . Am. Chem.
Soc. 1994, 116, 3180. (c) Uppenberg, J .; Ohrner, N.; Norin, M.; Hult,
K.; Kleywegt, G. J .; Patkar, S.; Waagen, V.; Anthonsen, T.; J ones, T.
A. Biochemistry 1995, 34, 16838.
(4) (a) Brieva, R.; Rebolledo, F.; Gotor, V. J . Chem. Soc., Chem.
Commun. 1990, 1386. (b) Chen, P. Y.; Wu, S. H.; Wang, K. T.
Biotechnol. Lett. 1993, 15, 181. (c) Theil, F.; Kunath, A.; Ramm, M.;
Reiher, T.; Schick, H. J . Chem. Soc., Perkin Trans. 1 1994, 1994, 1509.
(9) Garc´ıa, M. J .; Rebolledo, F.; Gotor, V. Tetrahedron: Asymm.
1993, 4, 2199.
(10) Puertas, S.; Rebolledo, F.; Gotor, V. J . Org. Chem. 1996, 61,
6024.
10.1021/jo981630a CCC: $18.00 © 1999 American Chemical Society
Published on Web 02/06/1999

Doubly Enantioselective Aminolysis Reactions
J . Org. Chem., Vol. 64, No. 5, 1999 1465
Sch em e 1
and B are the enantiomers of the ester, M and N the
enantiomers of the nucleophile, then the stereoisomers
of the product are AM, AN, BM, and BN. On the
assumption that A and M are the fast-reacting enanti-
omers, φES, cES, φNU, and cNU are calculated as shown in
eqs 3-6.
(AM + AN) - (BM + BN)
(AM + AN) + (BM + BN)
φES
)
(3)
(4)
(5)
(6)
eeES
cES
)
eeES + φES
(AM + BM) - (AN + BN)
(AM + BM) + (AN + BN)
eeNU
φNU
)
Moreover, in the search for an efficient doubly enanti-
oselective process, we also took into account the synthetic
utility of the products. Thus, the presence of a leaving
group (Cl) in the ester 1 allows further chemical trans-
formations of its derivatives.12 In addition, some optically
active 3-hydroxyglutarate derivatives have been used as
intermediates for the synthesis of several interesting
compounds,10,13 and optically active amines are useful
intermediates in the synthesis of drugs and crop-protect-
ing substances.11e
cNU
)
eeNU + φNU
Dou ble Resolu tion Rea ction s. CAL-catalyzed reac-
tions between ethyl (()-4-chloro-3-hydroxybutanoate [(()-
1] and (()-2a -c were carried out in 1,4-dioxane at 30
°C in the presence of 4 Å molecular sieves. In these
conditions, the lipase only catalyzed the aminolysis of (()-
1,15 and amides 3a -c were obtained, the (3S,1′R) isomer
being major in all cases (Scheme 1). The results are
summarized in Table 1.
Resu lts a n d Discu ssion
Some considerations have to be taken into account for
the treatment of the results obtained in the double kinetic
resolutions described herein. It is well-known that for a
simple kinetic resolution, a relationship exists between
the conversion c, the ee of the remaining substrate, eeS,
and that of the product, eeP (eq 1).14 For a double kinetic
resolution there is a similar relationship between c, eeS,
and the stereoisomeric composition of the product, simply
As shown in Table 1, in the reaction of (()-1 with (()-
2a , 31% of the starting material was transformed after
6 h (entry 1). The (3S,1′R):(3R,1′R) isomeric ratio of 99:1
obtained for the amide 3a implies that CAL is very
enantioselective toward the ester. Likewise the absence
of 1′S isomers of 3a indicates that the enantioselectivity
toward the amine 2a is even higher. As a consequence,
when the reaction was stopped at ca. 50% conversion
(entry 2), the amide (3S,1′R)-3a was obtained with a high
diastereomeric ratio (97:3) and enantiopure. Moreover,
both remaining substrates 1 and 2a were also recovered
with very high ee at this conversion value. These results
show that a truly effective double kinetic resolution has
taken place, this being the first time that such a process
is reported.
eeS
c )
(1)
eeS + eeP
φES
)
(isomers derived from A) - (isomers derived from B)
(isomers derived from A) + (isomers derived from B)
There are two columns with conversion values in Table
1
(2)
1; cNMR is that measured in the H NMR spectrum of the
crude, and c is that calculated with eq 4. In all cases there
is a good agreement between those values and also with
the isolated yields of the amides (see Experimental
Section). Even though we checked that the stereoisomeric
composition of 3a was not altered during the isolation
and purification steps, the coincidence of the values of
cRMN and c corroborates this fact.
considering that the term eeP in eq 1 must be replaced
by a new term, which we have named φ (eq 2). As there
are two chiral substrates, we must define one eeS, one φ,
and one c for each one of them, that is, (eeES, φES, cES) for
the ester and (eeNU, φNU, cNU) for the nucleophile. Obvi-
ously, cES and cNU must have the same value if both
substrates are initially in equimolecular amounts. If A
The replacement of amine 2a by 2b (Table 1, entry 3)
did not affect the activity of the lipase but slightly altered
its enantioselectivity. The ee of the remaining ester was
lower than that in entry 2 (the percentages of conversion
being very similar), which means that the enantioselec-
tivity toward the ester slightly decreased when the amine
was changed. Nevertheless, the amide (3S,1′R)-3b was
also obtained with high diastereomeric ratio (96:4) and
enantiopure at a high conversion. Moreover, the amide
3b was free of the isomers derived from the amine (S)-
2b, thus indicating that the CAL was still totally enan-
tioselective toward the amine 2b. When amine 2c was
(11) See, for instance, (a) Garc´ıa, M. J .; Rebolledo, F.; Gotor, V.
Tetrahedron Lett. 1993, 34, 6141. (b) Puertas, S.; Brieva, R.; Rebolledo,
F.; Gotor, V. Tetrahedron 1993, 49, 4007. (c) J aeger, K. E.; Liebeton,
K.; Zonta, A.; Schimossek, K.; Reetz, M. T. Appl. Microbiol. Biotechnol.
1996, 46, 99. (d) Iglesias, L. E.; Sa´nchez, V. M.; Rebolledo, F.; Gotor,
V. Tetrahedron: Asymm. 1997, 8, 2675. (e) Balkenhohl, F.; Ditrich,
K.; Hauer, B.; Ladner, W. J . Prakt. Chem. 1997, 339, 381.
(12) (a) Zhou, B. N.; Gopalan, A. S.; Shieh, W. R.; Sih, C. J .;
VanMiddlesworth, F. J . Am. Chem. Soc. 1983, 105, 5925. (b) Patel, R.
N.; McNamee, C. G.; Banerjee, A.; Howell, J . M.; Robison, R. S.; Szarka,
L. J . Enzyme Microb. Technol. 1992, 14, 731.
(13) (a) Brooks, D. W.; Palmer, J . T. Tetrahedron Lett. 1983, 24,
3059. (b) Rosen, T.; Heathcock, C. H. Tetrahedron 1986, 42, 4909. (c)
Baader, E.; Wess, G.; Weber, M.; Teetz, V.; Saric, R.; Schussler, H.;
Bartmann, W.; Fehlhaber, H. W.; Bergmann, A.; Beck, G.; Kesseler,
K.; J endralla, H. Tetrahedron Lett. 1988, 29, 2563.
(15) When molecular sieves were not used, a small amount of
4-chloro-3-hydroxybutanoic acid was also formed. In the absence of the
enzyme, starting materials were recovered unchanged.
(14) Chen, C. S.; Fujimoto, Y.; Girdaukas, G.; Sih, C. J . J . Am. Chem.
Soc. 1982, 104, 7294.

1466 J . Org. Chem., Vol. 64, No. 5, 1999
Sa´nchez et al.
Ta ble 1. CAL-Ca ta lyzed Am in olysis of (()-1 w ith (()-2a -c
ratio of stereoisomers of 3a -cb
a
entry
amine
t, h
cNMR
eeES
eeNU
(3S,1′R)
(3R,1′S)
(3R,1′R)
(3S,1′S)
cc
1
2
3
4
2a
2a
2b
2c
6
24
24
24
31
50
52
32
43
92
83
49
44
93
94
51
99
97
96
92
-
-
-
-
1
3
4
5
-
-
-
3
31
49
48
35
a
b
Calculated from the 1H NMR spectrum of the crude of reaction. Determined as described in the text. c Calculated from eqs 4 or 6.
Sch em e 2
Sch em e 3
Ta ble 2. CAL-Ca ta lyzed Am in olysis of 4 w ith (()-2a ,b
5a ,bb
a
entry amine t, h cNMR
eeNU (3S,1′R) (3R,1′R)
cc
The enantiomeric excesses of all the remaining sub-
strates (R)-1 and (S)-2a -c were determined by chiral
HPLC (see the Experimetal Section for conditions) after
transforming them into suitable derivatives [(R)-6, (S)-
7a ,b, and (S)-8c].
The absolute configuration of the remaining ester (R)-1
and amine (S)-2c were determined by comparison of their
optical rotations with reported values.12a,16 For the re-
maining amines 2a ,b, the S configuration was assigned
by comparison of the retention times obtained in the
HPLC analyses of their carbamates 7a ,b with those of
samples of known configuration.
As the remaining ester 1 had the R configuration, and
the remaining amines 2a -c had the S configuration, the
major stereoisomer of the enzymatically synthesized
amides 3a -c necessarily had the (3S,1′R) configuration.
The absolute configuration of amidoester 5a was
established as follows. As the remaining amine 2a had
the S configuration, the configuration at C-1′ had to be
R. To determine the configuration at C-3, the diastere-
omeric mixture (3S,1′R)- and (3R,1′R)-5a was synthesized
from 4 and (R)-2a and subsequently converted into the
O-acetyl derivative. Its 1H NMR spectrum gave two peaks
at 1.89 and 1.91 ppm for the mixture of the diastereo-
mers. The O-acetyl derivative of the enzymatically syn-
thesized amidoester 5a gave only one peak at 1.89 ppm,
which corresponds to the (3S,1′R) isomer.17 Similarly, the
configuration at carbon 1′ of amidoester 5b was R
because the remaining amine 2b had the S configuration.
Taking into account that the CAL always forms the 3S
isomer of the resulting amidoester when 4 reacts with
different nucleophiles, such as ammonia, achiral amines,10
and amine 2a , the configuration at C-3 of 5b was
1
2
2a
2b
24
30
86
85
75
72
98
96
2
4
86
84
a
Calculated from the 1H NMR spectrum of the crude products
b
of the reaction and referred to the diester 4. Ratio of stereoiso-
mers of 5a ,b stereoisomers (3S,1′S) and (3R,1′S) were not detected.
Calculated from eq 6.
c
used (Table 1, entry 4), amide (3S,1′R)-3c was isolated
with a high diastereomeric ratio (92:8) and enantiopure,
though the reaction rate and the enantioselectivity were
lower than in the previous cases. The remaining sub-
strates were recovered with low enantiomeric excesses
because the conversion (35%) was still far from 50%.
Asym m etr iza tion -Resolu tion Rea ction s. These
processes were carried out with the prochiral substrate
4 and amines (()-2a ,b (Scheme 2) in the same conditions
as those for (()-1, but using a 2:1 molar ratio amine:
diester in order to allow the 100% conversion of the
diester. Although reactions were stopped when no ester
could be detected in TLC, some diester 4 remained
unreacted, as Table 2 shows. In both reactions the CAL
catalyzed the monoaminolysis of 4, the amidoesters 5a ,b
being the only products obtained. The lipase was totally
enantioselective toward the amines 2a ,b, exclusively
transforming the R enantiomer, as had happened in the
reactions with substrate (()-1. Moreover, the prochiral
selectivity for the ester was also high, 98:2 with amine
2a and 96:4 with 2b, amidoesters (3S,1′R)-5a ,b being
achieved with very high dr and enantiopure. As is
indicated in Table 2, there is a good agreement between
1
the conversions determined from the H NMR spectrum
of the crude (cNMR) and those calculated from eq 6 (c).
Deter m in a tion of th e Ster eoisom er ic Com p osi-
tion a n d Absolu te Con figu r a tion s. In Scheme 3 are
collected the most significant derivatives of the enzy-
matically prepared compounds that appear in this sec-
tion.
(16) Mazur, R. H. J . Org. Chem. 1970, 35, 2050.
(17) Santaniello, E.; Chiari, M.; Ferraboschi, P.; Trave, S. J . Org.
Chem. 1988, 53, 1567.

Doubly Enantioselective Aminolysis Reactions
J . Org. Chem., Vol. 64, No. 5, 1999 1467
assumed to be S. Therefore, the major isomer of the
enzymatically synthesized amidoester 5b was (3S,1′R).
The stereoisomeric composition of the amides 3a -c
and 5a ,b were all determined by HPLC. The mixtures
of the four stereoisomersstwo racemic diastereomerss
of the amides 3a -c and 5a ,b were obtained by AlCl3
catalyzed reaction of (()-2a -c with either (()-1 or 4.
These mixtures, that for the sake of brevity we named
rac-3a -c and rac-5a ,b , were used to find the optimal
conditions for the HPLC analysis. Whereas amides 3a ,
3c, and 5a were analyzed directly, the derivatization of
amides 3b and 5b was necessary. As the absolute
configurations of the minor stereoisomers were also
determined by HPLC, the analysis of each product is
discussed individually in the following paragraphs.
Am id e 3a . For rac-3a four peaks of relative areas 1.3:
1:1:1.3 (tR: 20.4, 24.5, 27.4, 31.1 min) were obtained with
the Chiralcel-OD column. These relative areas imply that
peaks at 20.4 and 31.1 min, as well as peaks at 24.5 and
27.4 min, were enantiomeric couples. The enzymatically
obtained amide 3a gave only two peaks at 20.4 and 24.5
min, with 99:1 relative areas, thus corresponding to the
peak at 20.4 min to the (3S,1′R) isomer. The comparison
of these retention times with those of the mixture of
diastereomers (3S,1′R)-3a and (3R,1′R)-3a , prepared by
AlCl3-catalyzed reaction of (()-1 and optically active (R)-
2a , showed that the minor stereoisomer of the enzymatic
sample was the (3R,1′R).
Am id e 3b. Amide 3b had to be transformed into its
O-benzoyl derivative 9b for its analysis. rac-9b gave three
peaks of relative areas 1:1:2 (tR: 15.2, 16.3, 18.9 min)
with the Chiralcel-OD column, which means that the
third peak contained two stereoisomers. Besides, the two
first peaks were partially overlapped. The enzymatic
sample 9b, which mainly contained the (3S,1′R) isomer,
gave only one peak at 15.2 min. Due to the partial
overlapping, the presence of a small amount of the
stereoisomer at 16.3 min could not be discarded. As
nothing was detected at 18.9 min, it must be concluded
that the enzyme only formed either one or two out of the
four possible stereoisomers of the amide. To decide
whether there were one or two isomers, the two samples
of 9bsrac and enzymaticswere analyzed with an achiral
HPLC column (Lichrosorb). rac-9b gave two peaks of
equal areas at 8.8 and 10.7 min, whereas the enzymatic
sample gave the same two peaks but with relative areas
4:96. This means that only two stereoisomers were
formed by the enzyme, and that they were diastereomers.
Moreover, as the enantiomeric excess of the remaining
amine (S)-2b was higher than that of the remaining ester
(R)-1 (see Table 1, entry 3), the configuration of the minor
isomer must be (3R,1′R).
F igu r e 1. HPLC chromatograms of compounds 10 (with
Lichrosorb column) and 11 (with Chiralcel OD column). A: rac-
10. B: Chemoenzymatically synthesized 10; relative area 96:
4. C: rac-11. D: Chemoenzymatically synthesized 11; relative
area 96:4.
Am id e 5a . For rac-5a four peaks of equal areas (tR:
21.0, 25.7, 29.0, 30.6 min) were obtained with the
Chiralcel-OD column. The enzymatically obtained amide
5a gave only two peaks at 21.0 and 25.7 min of relative
area 98:2. Comparison of these retention times with those
of the mixture of (3S,1′R)- and (3R,1′R)-5a , obtained by
AlCl3-catalyzed reaction of 4 and optically active (R)-2a ,
showed that the major stereoisomer of the enzymatic
sample was the (3S,1′R) and that the minor stereoisomer
was the (3R,1′R).
Am id e 5b. The stereoisomers of this compound were
not resolved in the HPLC chiral column. Several deriva-
tives of 5b were prepared, but none of them gave a good
separation of the four stereoisomers in the available
columns. However, the combination of the results for two
different derivatives of 5b, the MTPA ester 10 and the
O-(2-thienylcarbonyl) ester 11, allowed us to determine
the stereoisomeric composition of the enzymatically
obtained 5b (Figure 1).
From chromatogram B we deduced that there was a
96% of the major stereoisomer and that the other 4% may
correspond either to one or to two stereoisomers. To
decide whether the minor peak corresponded to one or
to two isomers, derivative 11 was analyzed. As chromato-
gram D shows, there was a 4% amount of one single
stereoisomer. Therefore, the chemoenzymatically pre-
pared samples 10 and 11 were composed of only two out
of the four possible stereoisomers, in a 96:4 ratio. Finally,
the enzymatically synthesized 11 gave two peaks of
relative areas 96:4 when analyzed in an achiral column
(chromatogram not shown), indicating that those two
stereoisomers were diastereomers and not enantiomers.
In conclusion, the CAL transformed the R enantiomer
of the amines 2a -c, the S enantiomer of the ester 1, and
the pro-R group of ester 4, affording the amides 3a -c
and 5a ,b with (3S,1′R) configuration. The minor stere-
oisomers of the amides 3a and 5a were (3R,1′R), which
means that the lipase was totally enantioselective to the
amine 2a . On the basis of these results and on the fact
that the ee’s of the remaining amines (S)-2a -c were
always higher than those of the remaining ester (R)-1,
the same configuration (3R,1′R) for the minor stereoiso-
mer of the amides 3b,c and 5b was assumed. The
stereochemical preference of the CAL toward the R
Am id e 3c. For rac-3a four peaks of equal areas (tR:
29.7, 34.7, 37.7, and 40.4 min) were obtained with the
Chiralcel-OD column. The enzymatically obtained amide
3c, containing mainly the (3S,1′R) isomer, gave three
peaks at 29.7, 34.7, and 40.4 min, with relative areas of
5:92:3. As the enzymatic formation of the (3R,1′S) isomer
was highly improbable because the enzyme should have
accepted simultaneously the disfavored enantiomers of
the two substrates, the two minor isomers detected had
to be the (3S,1′S) and the (3R,1′R). The unequivocal
assignment of the peaks to these two enantiomers was
not possible; however, based on their relative areas and
on the ee’s of the remaining substrates, we tentatively
assigned them as shown in Table 1.

1468 J . Org. Chem., Vol. 64, No. 5, 1999
Sa´nchez et al.
Sch em e 4
of 3a -c, the hydroxyl group had to be protected in order
to prevent side reactions.24 Silylation of amides (3S,1′R)-
3a -c, and subsequent treatment of the O-silylated
amides (3S,1′R)-13a -c with NaH or t-BuOK, afforded
(3S,1′R)-14a -c in good yields.
The NMR spectra of compunds (4S,1′R)-14a ,b showed
the presence of only one diastereomer, thus ruling out
1
the possibility of epimerization. However, the H NMR
spectrum of (4S,1′R)-14c had a small amount of the
minor stereoisomer, due to the fact that its precursor
amide 3c had a 92:8 dr (see Table 1).
Con clu sion s
The work presented in this paper demonstrates that
doubly enantioselective enzymatic reactions can be ef-
ficiently performed with a rational selection of the
enzyme, substrates, and experimental conditions. Besides
the interest of these reactions from the enzymatic point
of view, these enzymatic processes have a great synthetic
value because the diastereo- and enantioselective forma-
tion of one product, starting from racemic substrates, is
achieved in one single step. Moreover, the enzymatically
formed products are useful for the chemoenzymatic
synthesis of some interesting optically active hetero-
cycles.
enantiomer of the amines follows the rule proposed by
Kazlauskas for secondary alcohols and the isosteric
primary amines.18
Syn th esis of 3-Hyd r oxyp yr r olid in es a n d 4-(Sily-
loxy)-2-oxop yr r olid in es. Optically active 4-chloro-3-
hydroxybutanamides obtained in this work could be
transformed by reduction into 1,3-amino alcohols. Due
to the presence of the leaving group at C-4 position, the
resulting amine function could experiment a cyclization
reaction to yield 3-pyrrolidinols. Optically active 3-pyr-
rolidinols are constituents of several bioactive com-
pounds19 and can be used as intermediates for the
synthesis of other interesting molecules.20
Exp er im en ta l Section
Gen er a l. Candida antarctica lipase B, SP 435, was donated
by Novo Nordisk Co. It was kept under vacuum (rt, 10-4 Torr)
for 2 days before use. All reagents were purchased from Aldrich
Chemie. Solvents were distilled over a suitable desiccant and
stored under nitrogen. Flash chromatography was performed
using Merck silica gel 60 (230-400 mesh). Chiral HPLC
analyses were performed using a Chiralcel OD column (Daicel).
For nonchiral HPLC analyses, a Lichrosorb column was used.
Gen er a l P r oced u r e for th e En zym a tic Am in olysis of
(()-1. Ester (()-1 (5 mmol, 833 mg) and the corresponding
amine (()-2a -c (5 mmol) were added to a suspension of CA
lipase (1 g) and 700 mg of 4 Å molecular sieves (activated
powder) in 1,4-dioxane (20 mL) under nitrogen atmosphere.
The suspension was shaken at 30 °C and 250 rpm until the
desired conversion was reached. At completion, the enzyme
and the molecular sieves were filtered over a Celite pad and
washed with CH2Cl2 (4 × 10 mL). HCl(g) was bubbled through
the organic solution to form the corresponding amine hydro-
chloride, which was extracted with H2O (5 mL). The aqueous
phase was washed with CH2Cl2 (2 × 5 mL) to minimize the
loss of amide 3a -c. The combined organic extracts were dried,
evaporated, and analyzed by 1H NMR to determine the
conversion. Finally, the remaining substrate (S)-1 and the
product (3S,1′R)-3a -c were separated by flash chromatogra-
phy (hexane:AcOEt 1:1). Yields of amides 3a -c are referred
to the initial amount of ester 1.
Treatment of amides (3S,1′R)-3a -c with BH3‚THF21
gave the corresponding pyrrolidinols (3S,1′R)-12a -c
(Scheme 4) with very high yields (96% for 12a and 12c)
and high purity in most cases. To ensure that no
significant epimerization occurred during the cyclization
step, the 1.3:1 mixture of diastereomers of amide rac-3a
1
was transformed into pyrrolidinol rac-12a . Its H NMR
spectrum in CDCl3 showed separate signals for the Hb
proton (see Scheme 4) of the two diastereomers at 2.76
(dd) and 2.97 (dd) ppm, respectively. In contrast, the
spectrum of the chemoenzymatically synthesized pyrro-
lidinol (3S,1′R)-12a showed only the signal at 2.76 ppm,
which excluded the presence of the minor diastereomer.
Therefore, no significant racemization of any of the two
stereogenic centers occurred during the cyclization step.
The enzymatically obtained amides 3a -c are also
immediate precursors of γ-lactams. Optically active γ-lac-
tams are used as synthetic intermediates22 and as chiral
auxiliaries.23 As a base was required for the cyclization
(3S,1′R)- 4-Ch lor o-3-h yd r oxy-N-(1-p h en yleth yl)bu ta n -
a m id e (3a ). Yield, 45%. White solid; mp 88-90 °C; [R]25
(18) Kazlauskas, R. J .; Weissfloch, A. N. E.; Rappaport, A. T.; Cuccia,
L. A. J . Org. Chem. 1991, 56, 2656.
D
+53.0 (c 1.0, CHCl3), >99% ee, 99:1 dr; IR (KBr): 3443, 1642
(19) (a) Welstead, J ., W J .; Helsley, G. C.; Duncan, R. L.; Cale, J ., A
D.; Taylor, C. R.; DaVanzo, J . P.; Franko, B. V.; Lunsford, C. D. J .
Med. Chem. 1969, 12, 435. (b) Lunsford, C. D., Brit. Pat. 1, 170, 831,
1969; Chem. Abstr., 1970, 72: 78862P. (c) Hirose, Y.; Kariya, K.;
Sasaki, I.; Kurono, Y.; Achiwa, K. Tetrahedron Lett. 1993, 34, 5915.
(20) Sleevi, M. C.; Cale, A. D.; Gero, T. W.; J aques, L. W.; Welstead,
W. J .; J ohnson, A. F.; Kilpatrick, B. F.; Demian, I.; Nolan, J . C.;
J enkins, H. J . Med. Chem. 1991, 34, 1314.
(21) Barrett, A. G. M. In Comprehensive Organic Synthesis; Trost,
B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 8, p 249.
(22) (a) Koot, W. J .; Vanginkel, R.; Kranenburg, M.; Hiemstra, H.;
Louwrier, S.; Moolenaar, M. J .; Speckamp, W. N. Tetrahedron Lett.
1991, 32, 401. (b) Rotella, D. P. Synlett 1996, 479. (c) Klaver, W. J .;
Hiemstra, H.; Speckamp, W. N. Tetrahedron Lett. 1987, 28, 1581.
(23) Davies, S. G. Doisneau, G. J . M. Prodger, J . C. Sanganee, H. J .
Tetrahedron Lett. 1994, 35, 2369.
1
cm-1; H NMR (CDCl3) δ 1.48 (3H, d, J ) 7.0 Hz), 2.38-2.57
(2H, m), 3.40-3.65 (2H, m), 4.17 (1H, m), 5.09 (1H, m), 6.32
(1H, br d, J ) 6.7 Hz), 7.20-7.42 (5H, m); 13C NMR (CDCl3) δ
21.83, 39.40, 48.07, 48.79, 68.37, 125.82, 127.19, 128.50,
142.85, 170.40; MS m/z 241 (M+, 80), 120 (71), 106 (100), 105
(97). Anal. Calcd for C12H16ClNO2: C, 59.63; H, 6.67; N, 5.79.
Found: C, 59.76; H, 6.58; N, 5.52.
(3S,1′R)- 4-Ch lor o-N-[1-(2-fu r yl)et h yl]-3-h yd r oxyb u -
ta n a m id e (3b). Yield, 44%. White solid; mp 86-87 °C; [R]25
D
+83.5 (c 1.0, CHCl3), >99% ee, 96:4 dr; IR (KBr): 3350, 3283,
(24) For example, the epoxidation of the chlorohydrin and the
subsequent â-elimination and epoxide opening.

Doubly Enantioselective Aminolysis Reactions
J . Org. Chem., Vol. 64, No. 5, 1999 1469
1640, 1549 cm-1; 1H NMR (CDCl3) δ 1.48 (3H, d, J ) 7.0 Hz),
2.41-2.62 (2H, m), 3.50-3.65 (2H, m), 4.20 (2H, m), 5.21 (1H,
m), 6.19 (1H, dt, J ) 0.9, 3.2 Hz), 6.25 (1H, br s), 6.31 (1H, dd,
J ) 1.8, 3.2 Hz), 7.34 (1H, dd, J ) 0.9, 1.8 Hz); 13C NMR
(CDCl3) δ 19.21, 39.38, 42.72, 48.02, 68.33, 105.50, 110.06,
141.70, 154.80, 170.32; MS m/z 231 (M+, 100), 110 (80), 95 (78).
Anal. Calcd for C10H14ClNO3: C, 51.84; H, 6.09; N, 6.05.
Found: C, 52.06; H, 6.20; N, 5.94.
Calcd for C12H17NO5: C, 56.46; H, 6.71; N, 5.49. Found: C,
56.56; H, 6.99; N, 5.49.
Gen er a l P r oced u r e for th e AlCl3-Ca ta lyzed Syn th esis
of Am id es r a c-3a -c a n d r a c-5a ,b a s Sta n d a r d s for th e
Ch ir a l HP LC An a lysis. The corresponding amine (()-2a -c
(9 mmol) was added over a stirred suspension of AlCl3 (4.5
mmol, 600 mg) in 1,2-dichloroethane (2 mL) at 0 °C. After
allowing to warm to room temperature, the corresponding
ester, (()-1 or 4 (3 mmol), was added. The mixture was stirred
overnight and quenched with water (2 mL). After stirring for
30 min, the mixture was filtered through Celite and the
organic phase separated. The aqueous phase was extracted
with dichloromethane, and the combined organic phases were
dried (Na2SO4) and concentrated. The crude product was
chromatographed using hexane:AcOEt 2:1 as eluent, affording
the correponding amides in 9-34% yield.
(3S,1′R)-4-Ch lor o-N-(2-h ep t yl)-3-h yd r oxybu t a n a m id e
(3c). Yield, 32%. White solid, mp 70-72 °C; [R]25D -24 (c 0.95,
CHCl3), >99% ee, 92:8 dr; IR (KBr): 3350, 1636, 1555 cm-1
;
1H NMR (CDCl3) δ 0.89 (3H, t, J ) 6.7 Hz), 1.14 (3H, d, J )
6.5 Hz), 1.20-1.39 (6H, m), 1.39-1.51 (2H, m), 2.43-2.55 (2H,
m), 3.51-3.63 (2H, m), 3.99 (1H, m), 4.19 (1H, m), 4.34 (1H,
d, J ) 4.7 Hz), 5.62 (1H, br s); 13C NMR (CDCl3) δ 13.52, 20.22,
22.07, 25.26, 31.18, 36.09, 39.41, 44.90, 47.84, 68.19, 170.29;
MS m/z 235 (M+, 5), 186 (38), 166 (42), 164 (83), 44 (100). Anal.
Calcd for C11H22ClNO2: C, 56.04; H, 9.41; N, 5.94. Found: C,
56.15; H, 9.28; N, 5.71.
(3S,1′R)-3-Hydr oxy-N-(1-ph en yleth yl)pyr r olidin e (12a).
Over a solution of amide (3S,1′R)-3a (0.7 mmol, 169 mg) in
anhydrous THF (20 mL) was added 1 M BH3‚THF (2 mL). The
reaction mixture was refluxed under nitrogen for 4 h. Then,
the excess of borane was destroyed at room temperature with
H2O (2 mL). After distilling the solvents at reduced pressure,
the resulting solid was dissolved in 6 N HCl (5 mL) and
refluxed for 3 h. The solvent was evaporated at reduced
pressure, and, finally, the remaining solid was dissolved in
5% LiOH (5 mL) and extracted with dichloromethane. The
organic phase was dried and concentrated to yield 129 mg
Ch ir a l HP LC An a lysis of th e Rem a in in g Su bstr a tes
of th e En zym a tic Rea ction s. Eth yl (R)-4-Ch lor o-3-h y-
d r oxybu ta n oa te (1). [R]25 +21.0 (c 1.0, CHCl3, 99% ee).
D
Lit.12a for (S)-1: [R]25 -11.7 (c 5.75, CHCl3, 55% ee). The
D
enantiomeric excess was determined by chiral HPLC analysis
of its O-benzoyl derivative (R)-6: tR 14.3 min; for (()-6 tR 13.0
and 14.3 min; Rs 2.2 (n-hexane:propan-2-ol 96:4, 0.5 mL/min).
(S)-1-P h en yleth yla m in e (2a ). The hydrochloride of (S)-
2a was conventionally transformed into its benzyl carbamate
(S)-7a ,25 which was analyzed by chiral HPLC: tR 13.1 min;
for (()-7b tR 13.1 and 15.2 min; Rs 2.8 (n-hexane:propan-2-ol
90:10, 0.8 mL/min). For the assignment of the HPLC peaks,
enantiopure (R)-7a was synthesized from commercial (R)-2a .
(96%) of the pure product. White solid; mp 75-77 °C; [R]25
D
+34.8 (c 1.0, CHCl3); IR (KBr): 3200 cm-1; H NMR (CDCl3)
1
δ 1.35 (3H, d, J ) 6.4 Hz), 1.65 (1H, m), 2.08 (1H, m), 2.37
(1H, m), 2.51 (1H, dd, J ) 5.6, 10.5 Hz), 2.64 (1H, m), 2.76
(1H, dd, J ) 2.5, 10.5 Hz), 3.26 (1H, q, J ) 6.7 Hz), 3.90 (1H,
br s, OH), 4.23 (1H, m), 7.12-7.31 (5H, m); 13C NMR (CDCl3)
δ 22.52, 34.43, 51.32, 61.52, 65.40, 70.57, 126.86, 126.98,
128.14, 144.41; MS m/z 191 (M+, 9), 176 (100), 105 (73). Anal.
Calcd for C12H17NO: C, 75.35; H, 8.96; N, 7.32. Found: C,
74.43; H, 8.71; N, 7.12.
For (S)-7a : [R]25 -35.2 (c 1.0, CHCl3, 93% ee).
D
(S)-2-F u r yleth yla m in e (2b). The hydrochloride of (S)-2b
was transformed into its benzyl carbamate (S)-7b,25 which was
analyzed by chiral HPLC:11d tR 14.8 min; for (()-7b tR 14.8 and
17.0 min; Rs 2.6 (n-hexane:propan-2-ol 90:10, 0.6 mL/min). For
(3S ,1′R )-N -[1-(2-F u r yl)e t h yl]-3-h yd r oxyp yr r olid in e
(12b). Prepared as described for 12a , except that the acid
treatment was carried out using 3 N HCl, stirring the mixture
for 1 h at room temperature. The reaction crude was purified
by flash chromatography using CH2Cl2:MeOH:(30% NH4OH)
400:30:1 as eluent, obtaining a 69% yield of the pure product.
(S)-7b: [R]25 -59.6 (c 1.0, CHCl3, 94% ee).
D
(S)-2-Hep tyla m in e (2c). [R]25D +0.4 (c 10, MeOH, 51% ee).
Lit.16 for (R)-2c: [R]25 -0.8 (c 10, MeOH). The enantiomeric
D
excess was determined by chiral HPLC analysis of its benza-
mide derivative (S)-8c, obtained by treatment of (S)-2c with
benzoyl chloride and pyridine: tR 13.6 min; for (()-8c tR 12.1
and 13.6 min; Rs 1.9 (n-hexane:propan-2-ol 95:5, 1 mL/min).
White solid; mp 49-50 °C; [R]25 +36.9 (c 1.0, CHCl3); IR
D
(KBr): 3424 cm-1; 1H NMR (CDCl3) δ 1.46 (3H, d, J ) 6.9 Hz),
1.72 (1H, m), 2.13 (1H, m), 2.48 (1H, m), 2.64 (1H, dd, J )
5.4, 10.3 Hz), 2.72-2.84 (2H, m), 2.90 (1H, br s, OH), 3.68 (1H,
q, J ) 6.9 Hz), 4.32 (1H, m), 6.17 (1H, d, J ) 3.0 Hz), 6.31
(1H, dd, J ) 1.8, 3.0 Hz), 7.35 (1H, dd, J ) 0.9, 1.8 Hz); 13C
NMR (CDCl3) δ 18.20, 34.26, 49.21, 55.77, 60.04, 70.39, 106.55,
109.70, 141.37, 155.52; MS m/z 181 (M+, 13), 166 (100), 95 (84).
Anal. Calcd for C10H15NO2: C, 66.27; H, 8.34; N, 7.73. Found:
C, 66.19; H, 8.51; N, 7.92.
For (S)-8c: [R]25 +9.0, (c 1.0, CHCl3, 51% ee).
D
Gen er a l P r oced u r e for th e En zym a tic Am in olysis of
4. The same procedure as for (()-1 was followed, except that
10 mmol of the racemic amines (()-2a ,b were used.
Met h yl (3S,1′R)-3-H yd r oxy-4-[N-(1-p h en ylet h yl)ca r -
ba m oyl]bu ta n oa te (5a ). Yield, 69%. White solid; mp 60-61
°C; [R]25 +62.2 (c 1.0, CHCl3), >99% ee, 98:2 dr; IR (KBr):
D
3400, 3331, 1726, 1643, 1530 cm-1; H NMR (CDCl3) δ 1.48
1
(3S,1′R)-N-(2-Hep tyl)-3-h yd r oxyp yr r olid in e (12c). Pre-
pared from (3S,1′R)-3c (0.7 mmol, 165 mg) as described for
(3H, d, J ) 6.9 Hz), 2.32-2.43 (2H, m, J ) 3.8, 8.1, 15.2 Hz),
2.44-2.57 (2H, m, J ) 4.9, 7.9, 16.1 Hz), 3.68 (3H, s), 4.16
(1H, d, J ) 3.5 Hz, OH), 4.38 (1H, m), 5.11 (1H, m), 6.49 (1H,
da, J ) 7.0 Hz, NH), 7.22-7.40 (5H, m); 13C NMR (CDCl3) δ
21.74, 40.60, 41.65, 48.46, 51.53, 65.06, 125.76, 128.32, 126.96,
142.98, 170.40, 172.06; MS m/z 265 (M+, 7), 120 (100), 106 (69),
105 (80). Anal. Calcd for C14H19NO4: C, 63.38; H, 7.22; N, 5.28.
Found: C, 63.27; H, 6.99; N, 5.21.
12a . Yield, 96%. Oil; [R]25 +15.9 (c 1.0, CHCl3); IR (neat):
D
3340 cm-1; H NMR (CDCl3) δ 0.82 (3H, t, J ) 6.9 Hz), 0.99
1
(3H, d, J ) 6.5 Hz), 1.10-1.48 (7H, m), 1.51 (1H, m), 1.66 (1H,
m), 2.09 (1H, m), 2.19-2.39 (2H, m), 2.52-2.70 (2H, m), 2.84
(1H, m), 3.54 (1H, br s, OH), 4.25 (1H, m); 13C NMR (CDCl3)
δ 13.95, 17.36, 22.53, 25.54, 32.04, 34.48, 34.78, 49.60, 58.72,
60.00, 70.60; MS m/z 184 [(M - 1)+, 35], 114 (100), 57 (42);
HRMS m/z calcd for C11H23NO 184.1701 (M - 1), found
184.1704.
Met h yl (3S,1′R)-4-{N-[1-(2-F u r yl)et h yl]ca r b a m oyl}-3-
h yd r oxybu ta n oa te (5b). Yield, 65%. White solid; mp 40-41
°C; [R]25 +82.1 (c 1.0, CHCl3), >99% ee, 96:4 dr; IR (KBr):
D
(3S,1′R)-3-(ter t-Bu tyld im eth ylsilyloxy)-4-ch lor o-N-(1-
p h en yleth yl)bu ta n a m id e (13a ). TBDMS chloride (1.4 mmol,
211 mg), imidazole (2.1 mmol, 143 mg), and a catalytic amount
of DMAP (5 mg) were added under nitrogen over a solution of
amide (3S,1′R)-3a (0.7 mmol, 169 mg) in dried dichlo-
romethane (3 mL). The reaction was stirred overnight and
stopped by the addition of a saturated aqueous solution of NH4-
Cl (5 mL). The aqueous phase was washed twice with dichlo-
romethane, and the combined organic extracts were dried and
concentrated. Flash chromatography of the crude product
(hexane:Et2O 2:1) afforded 227 mg (91%) of the pure product.
3295, 1730, 1647, 1547 cm-1; H NMR (CDCl3) δ 1.42 (3H, d,
1
J ) 7.0 Hz), 2.37 (2H, m), 2.48 (2H, m), 3.63 (3H, s), 4.17 (1H,
br s, OH), 4.34 (1H, m), 5.14 (1H, m), 6.13 (1H, d, J ) 3.2 Hz),
6.24 (1H, dd, J ) 1.9, 3.2 Hz), 6.51 (1H, da, J ) 8.6 Hz, NH),
7.28 (1H, dd, J ) 0.9, 1.9 Hz); 13C NMR (CDCl3) δ 19.17, 40.52,
41.67, 42.51, 51.59, 65.05, 105.29, 109.95, 141.62, 155.03,
170.38, 172.12; MS m/z 255 (M+, 4), 110 (100), 95 (61). Anal.
(25) Greene, T. W.; Wuts, P. G. M. Protecting Groups in Organic
Synthesis, 2nd ed.; J ohn Wiley & Sons: New York, 1991.

1470 J . Org. Chem., Vol. 64, No. 5, 1999
Sa´nchez et al.
White solid; mp 104-106 °C; [R]25 +45.6 (c 1.0, CHCl3); IR
δ -5.10, -5.01, 16.55, 17.67, 25.47, 41.81, 48.17, 51.70, 65.33,
127.07, 126.65, 128.32, 139.94, 172.25; MS m/z 262 (M+ - 57,
74), 158 (94), 105 (100). Anal. Calcd for C18H29NO2Si: C, 67.66;
H, 9.15; N, 4.38. Found: C, 67.55; H, 9.04; N, 4.58.
D
(KBr): 3267, 1640, 1561 cm-1; H NMR (CDCl3) δ 0.01 (3H,
1
s), 0.1 (3H, s), 0.82 (9H, s), 1.50 (3H, d, J ) 6.9 Hz), 2.42 (1H,
dd, J ) 6.2, 14.6 Hz), 2.57 (1H, dd, J ) 4.7, 14.6 Hz), 3.55
(2H, d, J ) 5.16 Hz), 4.32 (1H, m), 5.11 (1H, m), 6.20 (1H, br
s, NH), 7.32 (5H, m); 13C NMR (CDCl3) δ -5.08, -4.93, 17.76,
21.67, 25.50, 41.89, 47.98, 48.78, 69.36, 126.18, 128.52, 127.27,
142.76, 168.74; MS m/z 355 (M+, <1), 298 (M+-57, 49), 194
(84), 105 (100). Anal. Calcd for C18H30ClNO2Si: C, 60.73; H,
8.49; N, 3.93. Found: C, 60.72; H, 8.36; N, 3.83.
(4S,1′R)-4-(ter t-Bu tyld im eth ylsilyloxy)-N-[1-(2-fu r yl)-
eth yl]-2-oxop yr r olid in e (14b). Potassium tert-butoxide (0.6
mmol, 67 mg) was added portionwise over a solution of
(3S,1′R)-13b (0.6 mmol, 208 mg) in anhydrous THF (30 mL)
in an ice bath. The reaction mixture was allowed to warm and
stirred for 1 h. After adding 30 mL of a saturated aqueous
solution of NH4Cl, the product was extracted with Et2O (2 ×
30 mL). The combined organic extracts were dried and
concentrated. Flash chromatography of the crude product
(hexane:AcOEt 2:1) afforded 117 mg (63%) of the pure product.
Oil; [R]25D +77.8 (c 1.2, CHCl3); IR (KBr): 1647 cm-1; 1H NMR
(CDCl3) δ -0.02 (3H, s), 0.02 (3H, m), 0.81 (9H, s), 1.43 (3H,
d, J ) 7.3 Hz), 2.35 (1H, dd, J ) 16.8, 3.7 Hz), 2.62 (1H, dd, J
) 16.8, 6.4 Hz), 2.92 (1H, dd, J ) 3.1, 10.1 Hz), 3.49 (1H, dd,
J ) 10.1, 5.7 Hz), 4.4 (1H, m), 5.45 (1H, m), 6.21 (1H, dd, J )
1.1, 3.2 Hz), 6.28 (H, dd, J ) 1.9, 3.2 Hz), 7.32 (H, dd, J ) 1.1,
1.9 Hz); 13C NMR (CDCl3) δ -5.08, -5.01, 15.61, 17.68, 25.44,
41.52, 43.68, 51.79, 65.17, 106.61, 109.82, 141.98, 153.36,
172.02; MS m/z 252 (M+ - 57, 77), 158 (88), 95 (100); HRMS
m/z calcd for C16H27NO3Si 309.1760, found 309.1787.
(3S,1′R)-3-(ter t-Bu tyld im eth ylsilyloxy)-4-ch lor o-N-[1-
(2-fu r yl)eth yl]bu ta n a m id e (13b). Prepared from (3S,1′R)-
3b (0.7 mmol, 162 mg) as described for 13a . Yield, 228 mg
(94%). White solid; mp 62-64 °C; [R]25 +57.8 (c 0.8, CHCl3);
D
IR (KBr): 1640 cm-1
;
1H NMR (CDCl3) δ 0.03 (3H, s), 0.10
(3H, s), 0.83 (9H, s), 1.46 (3H, d, J ) 6.7 Hz), 2.33-2.62 (2H,
m), 3.52 (2H, d, J ) 5.5 Hz), 4.29 (1H, m), 5.19 (1H, m), 6.16
(1H, dt, J ) 3.4 Hz), 6.28 (1H, dd, J ) 1.8, 3.4 Hz), 6.44 (1H,
br d, NH), 7.31 (1H, dd, J ) 0.9, 1.8 Hz); 13C NMR (CDCl3) δ
-5.21, -4.98, 17.69, 19.46, 25.44, 41.78, 42.59, 47.89, 69.34,
105.53, 109.95, 141.59, 154.88, 168.74; MS m/z 345 (M+, 4),
288 (24), 194 (78), 95 (100), 75 (80). Anal. Calcd for C16H28
-
ClNO3Si: C, 55.55; H, 8.16; N, 4.05. Found: C, 55.34; H, 8.28;
N, 4.43.
(3S,1′R)-3-(ter t-Bu tyld im eth ylsilyloxy)-4-ch lor o-N-(2-
h ep t yl)bu t a n a m id e (13c). Prepared from (3S,1′R)-3c (0.7
mmol, 165 mg) as described for 13a . Yield, 206 mg (84%).
(4S,1′R)-4-(ter t-Bu tyld im eth ylsilyloxy)-N-(2-h ep tyl)-2-
oxop yr r olid in e (14c). Prepared from (3S,1′R)-13c (0.6 mmol,
210 mg) as described for 14a . Yield, 118 mg (62%). White solid;
White solid; mp 51-53 °C; [R]25 -6.1 (c 1.0, CHCl3); IR
mp 46-48 °C; [R]25D -9.2 (c 1.2, CHCl3); IR (KBr): 1669 cm-1
;
D
1
(KBr): 3269, 1640, 1555 cm-1; H NMR (CDCl3) δ 0.07 (3H,
1H NMR (CDCl3) δ 0.06 (6H, s), 0.86 (12H, s), 1.06 (3H, d, J )
6.8 Hz), 1.11-1.50 (8H, m), 2.32 (1H, dd, J ) 3.0, 16.8 Hz),
2.59 (1H, dd, J ) 6.2, 16.8 Hz), 3.07 (1H, dd, J ) 2.5, 10.4
Hz), 3.45 (1H, dd, J ) 5.4, 10.4 Hz), 4.22 (1H, m), 4.40 (1H,
m); 13C NMR (CDCl3) δ -5.03, -4.90, 13.96, 17.77, 18.29,
25.52, 22.44, 25.62, 31.55, 33.78, 41.94, 45.94, 51.05, 65.26,
172.26; MS m/z 298 (M+ - 15, 7), 256 (M+ - 57, 100), 242
(48), 214 (54). Anal. Calcd for C17H35NO2Si: C, 65.12; H, 11.25;
N, 4.47. Found: C, 64.98; H, 10.99; N, 4.35.
s), 0.10 (3H, s), 0.78-0.92 (12H, m), 1.09 (3H, d, J ) 6.5 Hz),
1.21-1.48 (8H, m), 2.36 (1H, dd, J ) 6.0, 15.0 Hz), 2.50 (1H,
dd, J ) 4.7, 15.0 Hz), 3.50 (2H, d, J ) 5.2 Hz), 3.91 (1H, m),
4.29 (1H, m), 5.88 (1H, br d, J ) 8.2 Hz, NH); 13C NMR (CDCl3)
δ -5.06, -4.96, 13.85, 17.75, 20.67, 22.37, 25.52, 31.51, 36.54,
25.52, 41.94, 45.06, 47.98, 69.38, 168.84; MS m/z 334 (M+
-
15, 4), 292 (M+ - 57, 100). Anal. Calcd for C17H36ClNO2Si: C,
58.34; H, 10.37; N, 4.00. Found: C, 58.23; H,10.28; N, 4.20.
(4S,1′R)-4-(ter t-Bu tyld im eth ylsilyloxy)-2-oxo-N-(1-p h e-
n yleth yl)p yr r olid in e (14a ). NaH (1 mmol, 24 mg) was added
over a solution of (3S,1′R)-13a (0.6 mmol, 214 mg) in anhy-
drous THF (30 mL) under nitrogen. The reaction mixture was
refluxed until the substrate was consumed (3 h). After cooling
to room temperature, saturated aqueous solution of NH4Cl (30
mL) was added and the product was extracted with Et2O (2 ×
30 mL). The combined organic extracts were dried and
concentrated. Flash chromatography of the crude product
(hexane:AcOEt 2:1) afforded 174 mg (91%) of the pure product.
Ack n ow led gm en t. We are grateful to the Direccio´n
General de Investigacio´n Cient´ıfica y Te´cnica (Project
BIO 95-0687) for financial support, and to Novo Nordisk
Co. for the generous gift of CA lipase.
Su p p or t in g In for m a t ion Ava ila b le: 1H and 13C NMR
spectra for compounds 12c and 14b, and HPLC chromato-
grams for compounds 3a ,c, 5a , and 9b (7 pages). This material
is contained in libraries on microfiche, immediately follows this
article in the microfilm version of the journal, and can be
ordered from the ACS; see any current masthead page for
ordering information.
White solid; mp 67-69 °C; [R]25 +70.3 (c 1.0, CHCl3); IR
D
(KBr): 1666 cm-1; 1H NMR (CDCl3) δ -0.05 (3H, s), 0.02 (3H,
s), 0.81 (9H, s), 1.49 (3H, d, J ) 7.2 Hz), 2.37 (1H, dd, J ) 2.2,
16.7 Hz), 2.65 (1H, dd, J ) 6.0, 16.7 Hz), 2.92 (1H, dd, J )
1.82, 10.3 Hz), 3.47 (1H, dd, J ) 5.2, 10.3 Hz), 4.39 (1H, m),
5.51 (1H, q, J ) 7.2 Hz), 7.20-7.35 (5H, m); 13C NMR (CDCl3)
J O981630A