Enantioselective enzymatic aminolysis and ammonolysis of dimethyl 3-hydroxyglutarate. Synthesis of (R)-4-amino-3-hydroxybutanoic acid

Full text of DOI:10.1021/jo960468d

6024
J . Org. Chem. 1996, 61, 6024-6027
Sch em e 1
En a n tioselective En zym a tic Am in olysis
a n d Am m on olysis of Dim eth yl
3-Hyd r oxyglu ta r a te. Syn th esis of
(R)-4-Am in o-3-h yd r oxybu ta n oic Acid
Susana Puertas, Francisca Rebolledo, and
Vicente Gotor*
Departamento de Quı´mica Orga´nica e Inorga´nica,
Universidad de Oviedo, E-33071, Oviedo, Spain
Received March 7, 1996
Enzymes are now widely recognized as practical cata-
lysts for asymmetric synthesis,1 their abilities to dis-
criminate between enantiotopic groups or faces of a
prochiral molecule being of particular importance. Hy-
drolysis, transesterification, or lactonization processes2
have been applied to prochiral diesters and diols in order
to prepare chiral synthons of high optical purity. How-
ever, the potential of enzymes, especially lipases, to
catalyze the aminolysis of prochiral substrates has not
hitherto been investigated.
With this in mind, the main purpose of this work is
the study of the aminolysis and ammonolysis reactions
of a prochiral diester, dimethyl 3-hydroxyglutarate (1).
Optically active derivatives of 1 have proven utility in
the synthesis of natural products; for example (R)- and
(S)-3-hydroxyglutaric acid monoalkyl esters are starting
materials in the synthesis of pimaricin,3 the lactone
portion of compactin, and other mevinic acids.4 In
addition, compounds derived of the aminolysis and am-
monolysis of 1, since they bear an amide function, could
be suitable precursors of biologically active amino acids,
amino alcohols, and other polyfunctionalized compounds.
We have chosen as biocatalyst the lipase from Candida
antarctica (CAL), which has shown already a great
efficiency in the resolution of both chiral esters5 and
chiral amines and diamines6 through aminolysis and
ammonolysis processes.
aminolysis and ammonolysis of 1, thus affording enan-
tiopure monoamidation products (3) with very high
yields. In all the cases, the reaction stopped at the amido
ester stage and diamides never were detected. Other
solvents such as hexane (for the aminolysis reactions) and
diisopropyl ether and THF (for the ammonolysis) were
also used but, for the same reaction time, the yields were
much lower than in 1,4-dioxane; for instance, a 98% yield
of 3a was reached after 24 h in hexane, whereas only 9
h were required in 1,4-dioxane. However, the change of
solvent did not influence on the enantioselectivity of the
enzyme; in all the solvents CAL only transformed the
pro-R ester grouping of 1, affording compounds (S)-3
independently of the amine used. Other lipases such as
Candida cylindracea and Pseudomonas cepacia were
checked in the reactions of 1 with 2a and 2d but, after 3
days of reaction, only starting materials were recovered.
The enantiopurity of compounds 3 was determined by
derivatization with (S)-3,3,3-trifluoro-2-methoxy-2-phen-
ylpropanoyl chloride (MTPA-Cl),7 to the corresponding
esters 4, whose 19F NMR spectra showed only one fluorine
signal. In contrast, MTPA-esters derived from rac-38
showed two well resolved fluorine resonances.9
CAL-catalyzed aminolysis and ammonolysis reactions
of 1 were carried out in 1,4-dioxane, with amines (2a -c)
at 30 °C and ammonia (2d ) at room temperature (Scheme
1), until disappearance of the starting diester (TLC
monitoring). In these conditions, CAL proved to be an
exceedingly effective catalyst either for the asymmetric
To assign the absolute configuration of the enzymati-
cally prepared amido esters 3, product 3a was conven-
tionally acetylated to 5a (Scheme 1), and this compound
was compared with another sample obtained from a
stereochemically well defined precursor, namely the
acetylated monoacid 7 (Scheme 2). Thus, after chemical
acetylation of 1, the resulting acetylated diester 6 was
subjected to CAL-catalyzed hydrolysis in phosphate
(1) (a) Wong, C.-H.; Whitesides, G. M. Enzymes in Synthetic Organic
Chemistry; Tetrahedron Organic Chemistry Series Vol. 12; Baldwin,
J . E., Ed.; Pergamon: New York, 1994. (b) Faber, K. Biotransforma-
tions in Organic Chemistry, 2nd ed.; Springer-Verlag, New York, 1995.
(2) For typical examples see: (a) Toone, E. J .; Werth, M. J .; J ones,
J . B. J . Am. Chem. Soc. 1990, 112, 4946. (b) Shapira, M.; Gutman, A.
L. Tetrahedron: Asymmetry 1994, 5, 1689. (c) Guanti, G.; Banfi, L.;
Narisano, E. J . Org. Chem. 1992, 57, 1540. (d) Tsuji, K.; Terao, Y.;
Achiwa, K. Tetrahedron Lett. 1989, 30, 6189. (e) Gutman, A. L.; Zuobi,
K.; Bravdo, T. J . Org. Chem. 1990, 55, 3546.
(7) Dale, J . A.; Dull, D. L.; Mosher, H. S. J . Org. Chem. 1969, 34,
2543.
(3) Brooks, D. W.; Palmer, J . T. Tetrahedron Lett. 1983, 24, 3059.
(4) (a) Rosen, T.; Heathcock, C. H. Tetrahedron 1986, 42, 4909. (b)
Baader, E.; Bartmann, W.; Beck, G.; Bergmann, A.; Fehlhaber, H.-
W.; J endralla, H.; Kesseler, K.; Saric, R.; Schu¨ssler, H.; Teetz, V.;
Weber, M.; Wess, G. Tetrahedron Lett. 1988, 29, 2563.
(5) (a) Garc´ıa, M. J .; Rebolledo, F.; Gotor, V. Tetrahedron: Asym-
metry 1993, 4, 2199. (b) Zoete, M. C.; Kock-van Dalen, A. C.; Rantwijk,
F.; Sheldon, R. A. J . Chem. Soc., Chem. Commun. 1993, 1831. (c) Zoete,
M. C.; Ouwehand, A. A.; Rantwijk, F.; Sheldon, R. A. Rec. Trev. Chim.
Pays-Bas 1995, 114, 171.
(6) (a) Astorga, C.; Rebolledo, F.; Gotor, V. J . Chem. Soc. Perkin
Trans.1 1994, 829. (b) Garc´ıa, M. J .; Rebolledo, F.; Gotor, V. Tetrahe-
dron 1994, 50, 6935. (c) Reetz, M. T.; Dreisbach, C. Chimia 1994, 48,
570. (d) Chamorro, C.; Gonza´lez-Mun˜iz, R.; Conde, S. Tetrahedron:
Asymmetry 1995, 6, 2343.
(8) A small amount of rac-3a -c could be obtained when diester 1
and amines (2a -c) were allowed to react in hexane during 9 days in
the absence of the enzyme. To obtain rac-3d , diester 1 was dissolved
in a solution of ammonia in methanol and the mixture was kept at 5˚
C during 28 h.
(9) As an example, 19F NMR data for the diastereomeric MTPA-
esters derived of rac-3b: δ -72.04 and -71.93 ppm (CFCl3 as an
external standard). For 4b (obtained from optically active 3b) only one
signal to -72.04 ppm was observed.
(10) Configuration was assigned according to the sign of the previ-
ously reported optical rotation for (R)-(+)-monoacid 7: Santaniello, E.;
Chiari, M.; Ferraboschi, P.; Trave, S. J . Org. Chem. 1988, 53, 1567.
(11) The ee was determined by derivatization of (S)-7 with (R)-R-
methylbenzylamine using the strategy described below in the text, and
1H NMR analysis of the obtained mixture of diastereomeric amides.
S0022-3263(96)00468-9 CCC: $12.00 © 1996 American Chemical Society

Notes
J . Org. Chem., Vol. 61, No. 17, 1996 6025
Sch em e 2
In summary, we have demonstrated that C. antarctica
lipase is an excellent catalyst for the aminolysis of a
prochiral diester. Our procedure allows the synthesis of
enantiopure monoamides derived from dimethyl 3-hy-
droxyglutarate. These compounds (3) possess three
differentiated functional groups and can be versatile
chiral synthons. From 3d , following a very simple
procedure, both free (R)-GABOB and its Cbz-derivative
can be obtained in enantiomerically pure forms. The
availability of the starting material and the high yield
and enantiopurity of the intermediate 3d make this
synthesis of (R)-GABOB an interesting alternative to
other asymmetric syntheses of this compound15 and,
especially, to those syntheses of (R)-GABOB via optical
resolution of racemates.16
buffer-1,4-dioxane, which afforded only the acetylated
monoacid (S)-(-)-710 with very good yield and 80% ee.11
The one-pot successive treatments of (S)-7 with oxalyl
chloride and catalytic amounts of DMF, and with ben-
zylamine (2a ), led to the acetylated amido ester (S)-5a .
An alternative approach to 5a from 1 by changing the
order of the two first steps (first, CAL-catalyzed hydroly-
sis; second, acetylation) was discarded because the low
optical purity (only 30% ee)12 of the intermediate hydroxy
monoacid 8.
Comparison of the signs of the optical rotations of both
compounds 5a obtained according to Schemes 1 and 2
clearly establishes the S-configuration for our product 3a .
For 3b and 3c it is assumed the S-configuration by
comparison of the 19F NMR signals of the Mosher’s esters
4a -c with those of the derived from rac-3a -c; in all the
cases the lower field signal disappears in the spectra of
optically active amides. The S-configuration for 3d was
assigned following the same strategy as for 3a .
In order to demonstrate the synthetic utility of optically
active compounds 3, the biologically active (R)-4-amino-
3-hydroxybutanoic acid [(R)-GABOB] (14) was synthe-
sized from 3d . The method, outlined in Scheme 3, mainly
involved a Hofmann rearrangement of the amide function
and a hydrolysis step. Hofmann rearrangement of 3d
was effectively accomplished with Hg(OAc)2 and NBS.13
However, the hydrolysis of the resulting oxazolidinone 9
through the smooth procedure described by Kunieda et
al.14 (N-tert-butoxycarbonylation and subsequent treat-
ment with Cs2CO3) did not lead to the desired cleavage
of the ring, but to methyl N-Boc-4-aminocrotonate (11)
as the sole product. Moreover, acid hydrolysis of 9
required drastic conditions (concd HCl, 24 h at 100 °C),
which determined the formation of racemic GABOB
together with its dehydration product.
These problems were resolved when the acetyl deriva-
tive 5d was subjected to the Hofmann rearrangement
instead of 3d , thus avoiding the formation of the cyclic
carbamate. To simplify the isolation and subsequent
hydrolysis of the rearranged product, the Hofmann
reaction of 5d was carried out with Hg(OAc)2, NBS, and
benzyl alcohol. In these conditions, the benzyl carbamate
12 was achieved and later hydrolyzed with 2 N HCl, to
give (R)-Cbz-GABOB (13). Finally, the hydrogenolysis
of compound 13 gave enantiopure (R)-GABOB (14) in
very good yield.
Exp er im en ta l Section
Gen er a l. C. antarctica lipase, SP 435, was donated by Novo
Nordisk Co. C. cylindracea and P. cepacia lipases were obtained
from Sigma Chemical Co. and Amano Pharmaceutical Co.,
respectively. All reagents were purchased from Aldrich Chemie.
Solvents were distilled over an adequate desiccant and stored
under nitrogen. Flash chromatography was performed using
Merck silica gel 60 (230-400 mesh).
Gen er a l P r oced u r e for th e Am in olysis of 1. Dimethyl
3-hydroxyglutarate (0.30 mL, 2 mmol) and 2 mmol of the
corresponding amine (2a -c) were added to a suspension of CA
lipase (180 mg) in 1,4-dioxane (7 mL) under nitrogen atmo-
sphere. The mixture was shaken at 30 °C and 250 rpm and
monitored by TLC. At completion (reaction times are indicated
in every case below), the enzyme was filtered and washed with
dichloromethane, and the combined organic solvents were
evaporated. The crude products 3a -c were essentially pure by
TLC and 1H NMR analyses. For analytical purposes, compounds
3a -c were purified by flash chromatography using hexane/ethyl
acetate 1:2 as eluent.
Meth yl (S)-4-(N-ben zylca r ba m oyl)-3-h yd r oxybu ta n oa te
(3a ): reaction time, 9 h; yield, 98%; mp 61-63 °C; [R]20 -3.8
D
(c 1.1, CHCl3); IR (Nujol) 1625, 1728 cm-1; H NMR (CDCl3) δ
1
(ppm) 2.37-2.63 (m, 4H, CH2), 3.35 (bs, OH), 3.71 (s, 3H, CH3),
4.34-4.55 (m, 3H, CH and CH2-N), 6.55 (bs, 1H, NH), 7.20-
7.45 (m, 5H, Ph); 13C NMR (CDCl3) δ (ppm) 40.58 (CH2), 41.74
(CH2), 43.10 (CH2), 51.63 (OCH3), 65.04 (CH), 127.20 (CH),
127.38 (CH), 128.43 (CH), 137.81 (C), 171.19 (CdO), 172.17
(CdO); MS (70 eV) m/ z (relative intensity) 251 (M+, 13), 106
(100), 91 (57). Anal. Calcd for C13H17NO4: C, 62.14; H, 6.82;
N, 5.57. Found: C, 62.31; H, 6.70; N, 5.45.
Met h yl (S)-4-(N-b u t ylca r b a m oyl)-3-h yd r oxyb u t a n oa t e
(3b): reaction time, 9 h; yield, 96%; oil; [R]20D -6.9 (c 1.2, CHCl3);
IR (neat) 1643, 1738 cm-1; 1H NMR (CDCl3) δ (ppm) 0.83-1.02
(t, 3H, CH3), 1.21-1.58 (m, 4H, CH2), 2.30-2.67 (m, 4H, CH2),
3.18-3.32 (m, 2H, CH2), 3.71 (s, 3H, CH3), 4.25-4.55 (m, 2H,
CH and OH), 6.42 (bs, 1H, NH); 13C NMR (CDCl3) δ (ppm) 13.36
(CH3), 19.70 (CH2), 31.07 (CH2), 38.81 (CH2), 40.70 (CH2), 41.69
(CH2), 51.44 (OCH3), 65.04 (CH), 171.24 (CdO), 171.97 (CdO);
HRMS m/ z calcd for C10H19NO4 217.1314, found 217.1316.
Anal. Calcd for C10H19NO4: C, 55.28; H, 8.81; N, 6.45. Found:
C, 55.12; H, 8.67; N, 6.58.
Met h yl (S)-4-(N-a llylca r b a m oyl)-3-h yd r oxyb u t a n oa t e
(3c): reaction time, 8 h; yield, 95%; oil; [R]20 -3.8 (c 1.03,
D
CHCl3); IR (neat) 1642, 1728 cm-1
;
1H NMR (CDCl3) δ (ppm)
2.35-2.67 (m, 4H, CH2), 3.71 (s, 3H, CH3), 3.85-3.96 (m, 2H,
CH2), 4.36-4.49 (m, 1H, CH), 4.70 (bs, 1H, OH), 5.08-5.27 (m,
2H, )CH2), 5.75-5.92 (m, 1H, )CH) 6.33 (bs, 1H, NH); 13C NMR
(CDCl3) δ (ppm) 40.70 (CH2), 41.38 (CH2), 41.75 (CH2), 51.48
(OCH3), 64.96 (CH), 115.75 (CH2), 133.61 (CH), 171.21 (CdO),
171.95 (CdO); HRMS m/ z calcd for C9H15NO4 201.1001, found
(12) The ee for 8, [R]20 +2.1 (c 1.0, CHCl3), as well as the
D
S-configuration were established by comparison of the optical rotation
with reported data in the literature for (R)-(-)-8, [R]23 -6.1 (c 0.64,
D
CHCl3): Rosen, T.; Watanabe, M.; Heathcock, C. H. J . Org. Chem.
1984, 49, 3657.
(15) (a) Kolb, H. C.; Bennani, Y. L.; Sharpless, K. B. Tetrahedron:
Asymmetry 1993, 4, 133. (b) Gopalan, A. S.; Sih, C. J . Tetrahedron
Lett. 1984, 25, 5235.
(16) Lu, Y.; Miet, C.; Kunesch, N.; Poisson, J . Tetrahedron: Asym-
metry 1990, 1, 707.
(13) J ew, S.-s.; Park, H. G.; Park, H.-J .; Park, M.-s.; Cho, Y.-s.
Tetrahedron Lett. 1990, 31, 1559.
(14) Ishizuka, T.; Kunieda, T. Tetrahedron Lett. 1987, 28, 4185.

6026 J . Org. Chem., Vol. 61, No. 17, 1996
Notes
Sch em e 3
201.1002. Anal. Calcd for C9H15NO4: C, 53.72; H, 7.51; N, 6.96.
Found: C, 53.82; H, 7.43; N, 7.11.
gave 0.91 g (46%) of the pure product. Mp 51-52 °C; [R]20D -3.0
(c 1.2, CHCl3); IR (neat) 1738 cm-1 1H NMR (CDCl3) δ (ppm)
;
2.60-2.75 (dd, 1H, CHH), 2.78-2.93 (dd, 1H, CHH), 3.24-3.37
(dd, 1H, CHH), 3.67 (s, 3H, OCH3), 3.71-3.83 (t, 1H, CHH),
4.88-5.03 (m, 1H, CH), 6.10 (bs, 1H, NH); 13C NMR (CDCl3) δ
(ppm) 38.97 (CH2), 45.67 (CH2), 52.01 (OCH3), 72.57 (CH), 159.50
(CdO), 169.67 (CdO). Anal. Calcd for C6H9NO4: C, 45.28; H,
5.70; N, 8.80. Found: C, 45.38; H, 5.82; N, 8.65.
Meth yl (S)-4-Ca r ba m oyl-3-h yd r oxybu ta n oa te (3d ). Am-
monia was bubbled through 1,4-dioxane (7 mL) at 0 °C for 10
min, after which CAL (180 mg) and 0.30 mL (2 mmol) of 1 were
added. The mixture was shaken at room temperature and 250
rpm for 5 h. Then, the enzyme was filtered and washed with
dichloromethane, and the combined organic solvents were
evaporated obtaining 3d (0.316 g, 98%), essentially pure by TLC
(R )-N -(t er t -Bu t oxyca r b on yl)-4-[(m e t h oxyca r b on yl)-
m eth yl]-2-oxooxa zolid in e (10). Et3N (0.63 mL, 4.5 mmol) and
DMAP (25 mg, 0.2 mmol) were added under nitrogen to a
solution of 9 (0.6 g, 3.8 mmol) and (Boc)2O (1.1 g, 5.0 mmol) in
THF (5 mL). After stirring at room temperature for 50 min,
the mixture was dissolved in dichloromethane, successively
washed with water, 2 N HCl, and water, and finally dried and
concentrated. Flash chromatography of the crude product
(hexane/ethyl acetate 3:1) gave 0.80 g (81%) of the pure product.
Mp 84-86 °C; [R]20D +5.8 (c 0.97, CHCl3); IR (Nujol) 1736, 1809
cm-1; 1H NMR (CDCl3) δ (ppm) 1.48 (s, 9H, CH3), 2.58-2.73 (dd,
1H, CHH), 2.79-2.92 (dd, 1H, CHH), 3.54-3.65 (dd, 1H, CHH),
3.67 (s, 3H, OCH3), 4.03-4.15 (dd, 1H, CHH), 4.73-4.88 (m, 1H,
CH); 13C NMR (CDCl3) δ (ppm) 27.81 (CH3), 38.68 (CH2), 48.39
(CH2), 52.12 (OCH3), 68.73 (CH), 83.93 (C), 149.14 (CdO), 151.24
(CdO), 169.24 (CdO); MS (70 eV) m/ z 259 (M+, <1), 244 (56),
203 (60), 159 (89), 57 (100). Anal. Calcd for C11H17NO6: C,
50.96; H, 6.61; N, 5.40. Found: C, 50.88; H, 6.73; N, 5.32.
Meth yl (R)-3-Acetoxy-4-[(ben zyloxyca r bon yl)a m in o]bu -
ta n oa te (12). BnOH (1.64 mL, 15.9 mmol) and a solution of
NBS (1.9 g, 10.7 mmol) in DMF (10 mL) were added under
nitrogen to a solution of 5d (1.6 g, 7.9 mmol) and Hg(OAc)2 (3.03
g, 9.5 mmol) in DMF (10 mL). The reaction was stirred for 22
h at 50 °C, and compound 12 was isolated using the same
procedure described for 9. The yield of 12 was 1.2 g (49%) after
flash chromatography (hexane/ethyl acetate 2:1). Mp 39-41 °C;
[R]20D +7.7 (c 0.94, CHCl3); IR (Nujol) 1688, 1732 cm-1; 1H NMR
(CDCl3) δ (ppm) 2.03 (s, 3H, CH3), 2.65 (d, 2H, CH2), 3.40-3.56
(m, 2H, CH2), 3.70 (s, 3H, OCH3), 5.08 (bs, 1H, NH), 5.11 (s,
2H, CH2), 5.20-5.37 (m, 1H, CH), 7.29-7.43 (m, 5H, Ph); 13C
NMR (CDCl3) δ (ppm) 20.70 (CH3), 36.06 (CH2), 43.31 (CH2),
51.71 (OCH3), 66.67 (CH2), 69.28 (CH), 127.93 (CH), 127.96 (CH),
128.31 (CH), 136.12 (C), 156.34 (CdO), 170.14 (CdO), 170.22
(CdO); MS (70 eV) m/ z 309 (M+, 26), 249 (59), 160 (78), 91 (100).
Anal. Calcd for C15H19NO6: C, 58.25; H, 6.19; N, 4.53. Found:
C, 58.19; H, 6.26; N, 4.41.
1
and H NMR analyses. For analytical purposes, 3d was purified
by flash chromatography using hexane/ethyl acetate/propan-2-
ol 2:8:1 as eluent. Mp 56-58 °C; [R]20 -4.2 (c 1.3, CHCl3); IR
D
(Nujol) 1665, 1726 cm-1
;
1H NMR (CDCl3) δ (ppm) 2.33-2.69
(m, 4H, CH2), 3.71 (s, 3H, CH3), 4.09 (bs, 1H, OH), 4.32-4.52
(m, 1H, CH), 6.04 (bs, 1H, NH), 6.38 (bs, 1H, NH); 13C NMR
(CDCl3) δ (ppm) 41.05 (CH2), 41.93 (CH2), 51.57 (OCH3), 64.89
(CH), 172.25 (CdO), 174.76 (CdO); MS (70 eV) m/ z (relative
intensity) 161 (M+, 1), 116 (38), 112 (41), 88 (62), 59 (100). Anal.
Calcd for C6H11NO4: C, 44.72; H, 6.88; N, 8.69. Found: C, 44.65;
H, 6.80; N, 8.53.
Meth yl (S)-3-a cetoxy-4-(N-ben zylca r ba m oyl)bu ta n oa te
(5a ) was prepared from 3a (0.125 g, 0.5 mmol) by reaction with
acetyl chloride (71 µL, 1 mmol) in a mixture of pyridine (81 µL,
1 mmol) and THF (3 mL) and in the presence of catalytic
amounts of DMAP (3 mg). At completion (TLC monitoring, 6 h
at rt), the reaction mixture was poured into water and the
product 5a extracted with ethyl acetate. Evaporation of the
organic solvent afforded 0.117 g (80%) of crude product, which
was purified by flash chromatography (hexane/ethyl acetate 1:1);
oil; [R]20D +3.3 (c 1.6, CHCl3); IR (neat) 1651, 1740 cm-1; 1H NMR
(CDCl3) δ (ppm) 2.00 (s, 3H, CH3), 2.62 (d, 2H, CH2), 2.65-2.91
(m, 2H, CH2), 3.68 (s, 3H, CH3), 4.43 (d, 2H, CH2), 5.40-5.56
(m, 1H, CH), 6.12 (bs, 1H, NH), 7.22-7.41 (m, 5H, Ph); 13C NMR
(CDCl3) δ (ppm) 20.84 (CH3), 37.97 (CH2), 40.24 (CH2), 43.46
(CH2), 51.75 (OCH3), 67.70 (CH), 127.42 (CH), 127.64 (CH),
128.57 (CH), 137.98 (C), 168.61 (CdO), 170.04 (CdO), 170.49
(CdO); HRMS m/ z calcd for C15H19NO5 293.1263, found 293.1270.
Meth yl (S)-3-a cetoxy-4-ca r ba m oylbu ta n oa te (5d ) was
prepared as described for 5a , with 2.5 h of reaction time. From
0.48 g (3 mmol) of 3d , compound 5d was obtained as an white
solid in 86% yield. For analytical purposes 5d was purified by
flash chromatography (ethyl acetate/methanol 9:1).
(S)-3-Acetoxy-4-(m eth oxyca r bon yl)bu ta n oic Acid (7). To
a mixture of phosphate buffer pH ) 7 (4 mL) and 1,4-dioxane
(1.5 mL) were added compound 6 (0.436 g, 2 mmol) and CAL
(180 mg). When the reaction was completed (1.5 h, TLC
monitoring), 3 N HCl and ethyl acetate were added. The organic
layer was separated and the aqueous layer extracted again with
ethyl acetate. The combined organic extracts were dried and
evaporated to yield compound 7 (0.39 g, 96%), which was purified
(R)-4-Ben zyloxyca r bon yla m in o-3-h yd r oxybu ta n oic Acid
(13). 2 N HCl (11 mL) was added to compound 12 (0.429 g, 1.39
mmol) and the mixture was heated at 50 °C. After 19 h, the
acid solution was extracted with ethyl acetate (3 × 15 mL). The
combined organic layers were dried and concentrated to give 13
(0.303 g, 86%) as a white solid, which was washed with hexane
and recristallyzed with ether-hexane. Mp 80-82 °C; [R]20D +4.7
by flash chromatography (hexane/ethyl acetate 3:4). Oil, [R]20
D
-4.4 (c 1.2, CHCl3), 80% ee. The spectral data for 7 were in
(c 0.29, CHCl3); IR (Nujol) 1672, 1696 cm-1 1H NMR (D2O) δ
;
accordance with literature values.10
(ppm) 2.18-2.37 (dd, 1H, CHH), 2.37-2.53 (dd, 1H, CHH), 2.95-
3.18 (m, 2H, CH2), 3.88-4.07 (m, 1H, CH), 4.96 (s, 2H, CH2),
7.15-7.40 (m, 5H, Ph); 13C NMR (CDCl3) δ (ppm) 38.39 (CH2),
45.74 (CH2), 67.02 (CH2), 67.38 (CH), 128.03 (CH), 128.14 (CH),
128.46 (CH), 136.05 (C), 157.24 (CdO), 175.75 (CdO); MS (70
(R)-4-[(Meth oxyca r bon yl)m eth yl]-2-oxooxa zolid in e (9).
A solution of NBS (3 g, 16.8 mmol) in DMF (10 mL) was added
under nitrogen to a solution of compound 3d (2 g, 12.4 mmol)
and Hg(OAc)2 (4.8 g, 15 mmol) in DMF (15 mL) and MeOH (16
mL). The reaction was stirred for 20 h at 50 °C and immediately
afterwards the white precipitate removed by filtration. The
solution was evaporated and the solid residue extracted with
dichloromethane. The organic solution was successively washed
with 10% NH4OH and water, dried, and concentrated. Flash
chromatography of the crude product (hexane/ethyl acetate 1:3)
eV) m/ z 253 (M+, 2), 108 (29), 91 (100). Anal. Calcd for C12H15
-
NO5: C, 56.91; H, 5.97; N, 5.53. Found: C, 57.02; H, 5.91; N,
5.45.
(R)-4-Am in o-3-h yd r oxybu ta n oic Acid (14). To a solution
of 122 mg of 13 (0.48 mmol) in ethanol (4 mL) was added Pd-C
(130 mg) and 1,4-cyclohexadiene (0.45 mL, 4.8 mmol), and the

Notes
J . Org. Chem., Vol. 61, No. 17, 1996 6027
mixture was heated under nitrogen at 40 °C for 4 h. Catalyst
was filtered on Celite and washed with water. Removal of the
solvents yielded compound 14 (55 mg, 96%) which was recrystal-
lized in a mixture ethanol-water. Mp 215-217 °C, [R]20D -20.2
BIO 95-0687) for financial support, and to Novo Nor-
disk Co. for the generous gift of the CA lipase.
(c 1.0, H2O), lit.15a mp 214 °C, [R]25 -20.7 (c 1.8, H2O). The
D
Su p p or t in g In for m a t ion Ava ila b le: 1H and 13C NMR
spectra for compounds 5a and 5d (3 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.
spectral data for 14 were in accordance with literature15a
values: 1H NMR (D2O) δ (ppm) 2.37 (d, 2H, CH2), 2.77 (dd, 1H,
CHH), 3.00 (dd, 1H, CHH), 3.93-4.13 (m, 1H, CH); 13C NMR
(D2O) δ (ppm) 43.01 (CH2), 44.80 (CH2), 66.22 (CH), 179.21
(CdO).
Ack n ow led gm en t. We are grateful to the Direccio´n
General de Investigacio´n Cient´ıfica y Te´cnica (Project
J O960468D