Enzymatic resolution of alicyclic β-lactams

Article abstract of DOI:10.1016/S0957-4166(00)00070-7

Racemates of N-hydroxymethylated β-lactams 4-6 were resolved through the lipase-catalyzed asymmetric acylation of the primary hydroxy group at the 6S stereogenic centre. High enantioselectivity (E>200) was observed when the enzymatic reactions were perfor

Full text of DOI:10.1016/S0957-4166(00)00070-7

Tetrahedron: Asymmetry 11 (2000) 1593±1600
Enzymatic resolution of alicyclic b-lactams
00
Judit Kaman, Eniko Forro and Ferenc Fulop*
Institute of Pharmaceutical Chemistry, University of Szeged, H-6701, Szeged, PO Box 121, Hungary
Received 8 February 2000; accepted 18 February 2000
Abstract
Racemates of N-hydroxymethylated b-lactams 4±6 were resolved through the lipase-catalyzed asym-
metric acylation of the primary hydroxy group at the 6S stereogenic centre. High enantioselectivity
(E>200) was observed when the enzymatic reactions were performed in acetone with lipase PS as catalyst
and vinyl butyrate as acyl donor. The hydrolysis of the enantiomeric azetidinones 4a±6a and 4b±6b resulted
in the enantiomerically pure alicyclic b-amino acids 4c±6c and 4d±6d. When the less reactive enantiomers
4b±6b were treated with NH4OH/MeOH, enantiomerically pure b-lactams 4e±6e were formed. # 2000
Elsevier Science Ltd. All rights reserved.
1. Introduction
The alicyclic b-amino acids, derived from the alicycle-condensed azetidinones, are of biological
importance, e.g. b-amino acids can be introduced into peptides in order to increase or modify
their biological activities.1,2 Through such exchanges, the stability of the natural peptides can be
increased. Among such amino acids, cispentacin, (1R,2S)-2-aminocyclopentanecarboxylic acid, is
a simple natural product with e€ective antifungal properties. This compound has been prepared,
for example, by enantioselective synthesis3 and enzymatic resolution.4 (1R,2S)-2-Amino-3-cyclo-
hexenecarboxylic acid was recently described as an anti-Candida agent.5 The (1R,2S) enantiomer
of 2-amino-4-cyclohexenecarboxylic acid is a key intermediate in the synthesis of carbapenem
antibiotics.6,7 (1R,2S)-2-Aminocyclohexanecarboxylic acid as part of a peptide exhibited thrombin-
inhibitory activity.8 Since these compounds are interesting from both chemical and pharmacological
aspects, our aim was to study the lipase-catalyzed resolution of 1±3 in order to obtain them in
optically active form and to hydrolyze them to the corresponding enantiomerically pure amino
acids. The unsaturated amino acids can also be functionalized, e.g. by making use of the reactivity
of the double bond.
* Corresponding author. Tel: 36 62 545564; fax: 36 62 420604; e-mail: fulop@pharma.szote.u-szeged.hu
0957-4166/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(00)00070-7

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1594
2. Results and discussion
There are several possibilities to resolve alicyclic-condensed azetidinones. Evans et al. investi-
gated the enantiospeci®c hydrolysis of (þ)-6-azabicyclo[3.2.0]hept-3-en-7-one. Even though a
large number of commercially available isolated enzymes proved unsuccessful, lactamases in a
special whole-cell preparation, ENZA-1 (Rhodococcus equi NCIB 40213), did give rise to the
enantioselective ring opening of this compound.9 If the lactam ring was activated with acyl-
protecting groups such as tert-butoxycarbonyl or acetyl, the lactam bond could be hydrolyzed
enantioselectively by numerous hydrolytic enzymes (esterases, lipases and proteases).10 One other
possibility to resolve such compounds is the enzyme-catalyzed kinetic resolution of the N-
hydroxymethylated derivatives. 5,5-Disubstituted hydantoins, substituted pyrrolidinones, pho-
topyridones and 2-azabicyclo[2.2.1]hept-5-en-3-ones have been prepared in enantiomerically
pure form. In these cases, the resolutions were based on the lipase PS or AK-catalyzed asym-
metric acylation of the primary hydroxy group or on the hydrolysis of the corresponding ester
derivatives.11 14
Since the preparation of N-hydroxymethyl derivatives of 4±6 (starting from 1±3) is simple4 and
the above group can easily be removed under basic reaction conditions, the possibilities of lipase-
catalyzed asymmetric acylation of 4±6 were investigated in the present work (Scheme 1).
Scheme 1. (i) Lipase PS, vinyl butyrate in acetone; (ii) 18% HCl, then ion-exchange chromatography; (iii) NH4OH/
MeOH
In order to ®nd the optimal conditions for gram-scale resolutions of 4±6, some preliminary
experiments were needed. The e€ects of enzyme, acyl donor and solvent on the enantioselectivity
and on the reaction rate in the enzymatic reactions were investigated for compound 4.

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1595
Lipase PS and lipase AK are the enzymes most commonly used in the resolution of alcohols
with remote stereocentres.15,16 As concerns the butyrylation of 4 under the same conditions,
lipase PS displayed a somewhat higher selectivity (Table 1, rows 2±5) than that with lipase AK.
The acylation of 4 with vinyl butyrate was also investigated in the presence of Novozym 435 in
tetrahydrofuran (THF). In this case, low enantioselectivity (after 45 min, conv.=43%, ees=32%,
eep=40%, E=3) was observed.
Table 1
E€ects of vinyl ester (0.2 M) and solvent on the acylation of 4 (0.1 M) in the presence of lipase
PS (25 mg ml^1), PSa or AKa (50 mg ml^1) at room temperature
One of the fundamental criteria of enzymatic kinetic resolution is the irreversibility of acyl
transfer. For this reason and on the basis of our previous studies,17 19 vinyl esters were used as
acyl donors. A better E value was observed when the lipase AK-catalyzed acylation of 4 was
performed with vinyl butyrate (VB) instead of vinyl acetate (VA) in acetone (Table 1, rows 1 and 2).
Organic solvents can also have marked e€ects on the reaction rate and the enantioselectivity of
enzymatic reactions. High enantioselectivities were observed in acetone, acetonitrile and THF
(Table 1). When the lipase PS-catalyzed butyrylations of 4 were performed in diethyl ether or
diisopropyl ether, higher reaction rates but lower enantioselectivities were observed (Table 1,
rows 8 and 9).
On the basis of the small-scale experiments (Table 1), the gram-scale resolutions of 4±6 were
performed in acetone with vinyl butyrate in the presence of lipase PS at room temperature. The
results are reported in Table 2 and in the Experimental. Although the stereogenic centre is two
atoms removed from the reaction centre, excellent selectivities (E>200) were observed in every
lipase PS-catalyzed gram-scale resolution (Table 2).
2.1. Absolute con®gurations
The stereochemistry was con®rmed in each set of compounds. Thus, treatment of 4a with 18%
25
.
HCl resulted in 4c HCl with speci®c rotation ‰ꢀŠD =±0.9 (c=0.51, MeOH). This is close to the value
of ^1 (c=0.59, MeOH) reported for (1R,2S)-2-aminocyclohexanecarboxylic acid hydrochloride.20

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Â
1596
Table 2
Lipase PSa (50 mg ml^1)-catalyzed resolution of 4±6 (0.1 M) in the presence of vinyl butyrate (0.2 M)
in acetone, at room temperature
.
Compound 4c HCl was puri®ed by ion-exchange chromatography and converted to amino acid
4c with ‰ꢀŠ2D5=±19.6 (c=0.25, H2O).
When 5b was hydrolyzed with 18% HCl, amino acid 5d was formed with ‰ꢀŠ2D5=+34 (c=0.27,
H2O). This value is close to the +36.4 (c=0.45, H2O) reported for (1S,2R) 2-amino-4-cyclo-
hexenecarboxylic acid.21
The hydrolysis of 6a resulted in amino acid 6c, which was converted into 4c by hydrogenation
in the presence of Pd/C in methanol.22 The resulting amino acid 4c was derivatized with TAGIT
reagent and its HPLC peak was found to be identical with that of 4c prepared by hydrolysis of
4a.23 The con®guration is therefore proved to be 1R,2S.
In conclusion, the lipase PS-catalyzed butyrylation of 4±6 displayed 6S selectivity.
3. Experimental
3.1. Materials and methods
The racemic alicyclic-condensed azetidinones 1±3 were obtained by cycloaddition of chloro-
sulfonyl isocyanate to the corresponding cycloalkenes.24 26 Vinyl acetate was purchased from
Aldrich Co. and vinyl butyrate from Fluka. Lipase PS and lipase AK were obtained from Amano
Pharmaceuticals, and Novozym 435 as an immobilized preparation from NOVO Nordisk. Before
use, lipase PS (5 g) and lipase AK (5 g) were dissolved in Tris±HCl bu€er (0.02 M; pH 7.8) in the
presence of sucrose (3 g), followed by adsorption on Celite (7 g; Sigma). The lipase preparations
thus obtained contained 20% (w/w) of lipase. All the solvents were of the highest analytical
grade. For gram-scale resolutions, acetone was dried over Na2SO4 for some days before use.
The ee values of the unreacted alcohols 4b±6b and the produced enantiomers of esters 4a±6a
and the enantiomerically pure azetidinones 4e±6e were determined by gas chromatography on a
Chrompack CP-Chirasil-DEX CB column (25 m).
For ion-exchange chromatography, Varion KS resin was used. The ee values of the amino acid
enantiomers 4c±6c and 4d±6d were determined by HPLC on an APEX ODS column (0.46 cmÂ25
cm, Jones Chromatography Ltd.), with 0.1% aqueous tri¯uoroacetic acid:methanol (1:1) as
eluent. For chiral derivatization, 2,3,4,6-tetra-O-acetyl-b-d-glucopyranosyl isothiocyanate
(TAGIT) was used, according to the literature.27

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1
Optical rotations were measured with a Perkin±Elmer 341 polarimeter. H NMR spectra were
recorded on a Bruker Avance DRX 400 spectrometer. Melting points were determined on a
Ko¯er apparatus.
3.2. Preparation of racemic 7-hydroxymethyl-7-azabicyclo[4.2.0]octan-8-one 4
7-Azabicyclo[4.2.0]octan-8-one 1 (2 g, 16 mmol) was dissolved in THF (40 ml). Paraformaldehyde
(0.58 g, 19.33 mmol), K2CO3 (0.22 g, 1.59 mmol) and H2O (1.6 ml) were added. The solution was
sonicated for 5 h. The solvent was evaporated o€ and the residue was dissolved in diethyl ether
(80 ml). The solution was dried over Na2SO4 and evaporated down. The residue was recrystal-
lized from diisopropyl ether at ^20ꢀC, but the resulting white crystalline product 4 (1.75 g, 11.29
1
mmol) melted at room temperature. H NMR (400 MHz, CDCl3) ꢁ (ppm): 1.46±1.90 (8H, m,
4ÂCH2), 3.20±3.24 (1H, m, H-1), 3.94±3.98 (1H, m, H-6), 4.54 (1H, d, CH2OH, J=11.6), 4.80
(1H, d, CH2OH, J=11.6). Anal. calcd for C8H13NO2: C, 61.91; H, 8.44; N, 9.02; found: C, 62.03;
H, 8.31; N, 9.09.
3.3. Preparation of racemic 7-hydroxymethyl-7-azabicyclo[4.2.0]oct-3-en-8-one 5
With the procedure described above, 7-azabicyclo[4.2.0]oct-3-en-8-one 2 (2 g, 16.26 mmol)
ꢀ
1
a€orded white crystals of 5 (1.63 g, 10.65 mmol, mp 59±61 C). H NMR (400 MHz, CDCl3) ꢁ
(ppm): 2.12±2.18 (2H, m, H-2a and H-5a), 2.42±2.56 (2H, m, H-2b and H-5b), 3.35±3.38 (1H, m,
H-1), 4.11±4.13 (1H, m, H-6), 4.50 (1H, d, CH2OH, J=11.7), 4.74 (1H, d, CH2OH, J=11.7),
5.69±5.86 (2H, m, CHCH). Analysis: calculated for C8H11NO2: C, 62.73; H, 7.24; N, 9.14; found:
C, 62.79; H, 7.13; N, 9.02.
3.4. Preparation of racemic 7-hydroxymethyl-7-azabicyclo[4.2.0]oct-4-en-8-one 6
With the procedure described above, 7-azabicyclo[4.2.0]oct-2-en-8-one 3 (2 g, 16.26 mmol)
ꢀ
1
a€orded white crystals of 6 (1.69 g, 11.04 mmol, mp 56±58 C). H NMR (400 MHz, CDCl3) ꢁ
(ppm): 1.58±1.61 (1H, m), 2.07±2.12 (3H, m), 3.46±3.53 (1H, m, H-1), 4.14 (1H, t, H-6, J=4.9),
4.43 (1H, d, CH2OH, J=11.6), 4.66 (1H, d, CH2OH, J=11.6), 6.01±6.20 (2H, m, CHCH). Anal.
calcd for C8H11NO2: C, 62.73; H, 7.24; N, 9.14; found: C, 62.51; H, 7.14; N, 9.21.
3.5. General procedure for a typical small-scale experiment
The appropriate N-hydroxymethyl-b-lactams 4±6 (0.1 M solution) in an organic solvent (1 ml)
were added to lipase PS (50 mg ml^1) or lipase AK (50 mg ml^1) or Novozym 435 (30 mg ml^1).
A vinyl ester (0.2 M in the reaction mixture) was added and the mixture was shaken at room
temperature. The progress of the reaction was followed by taking samples (0.1 ml) from the
reaction mixture at intervals and analyzing them by gas chromatography.
3.6. Gram-scale resolution of 4
Racemic 4 (1 g, 6.45 mmol) was dissolved in dry acetone (65 ml), lipase PS (3.25 g) and vinyl
butyrate (1.47 g, 12.90 mmol) were added and the mixture was stirred at room temperature. After
5 h, a few drops of triethylamine were added in order to enhance the stability of the unreacted

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1598
acid-labile 4b, and the enzyme was ®ltered o€ at 50% conversion. The acetone was evaporated
o€. The residue was chromatographed on silica, with elution with dichloromethane for separation
of the ester (1R,6S)-4a (0.58 g, 2.58 mmol; ‰ꢀŠ2D5=±15.5 (c=1, MeOH); ee=98%) as a pale-yellow
oil. Elution with dichloromethane:ethyl acetate (1:1) a€orded the unreacted (1S,6R)-4b (0.36 g,
25
1
2.32 mmol; ‰ꢀŠD =±31.7 (c=1, MeOH); ee=97%) as a colourless oil. H NMR (400 MHz,
CDCl3) ꢁ (ppm) for 4a: 0.95 (3H, t, CH3, J=7.4), 1.45±1.93 (10H, m, 4ÂCH2 and CH2CH2CH3),
2.31 (2H, t, CH2CH2CH3, J=7.4), 3.24±3.25 (1H, m, H-1), 3.87±3.88 (1H, m, H-6), 5.11 (1H, d,
CH2OCOPr, J=11.2), 5.18 (1H, d, CH2OCOPr, J=11.2). Anal. calcd for C12H19NO3: C, 63.98;
1
H, 8.50; N, 6.22; found: C, 64.03; H, 8.57; N, 6.28. The H NMR (400 MHz, CDCl3) ꢁ (ppm)
data for 4b are similar to those for (þ)-4. Anal. calcd for C8H13NO2: C, 61.91; H, 8.44; N, 9.02;
found: C, 61.80; H, 8.36; N, 9.05.
3.7. Gram-scale resolution of 5
With the procedure described above, the reaction of racemic 5 (1 g, 6.53 mmol) and vinyl
butyrate (1.48 g, 13.06 mmol) in dry acetone (65 ml) in the presence of lipase PS (3.25 g) for 4 h
a€orded the ester (1R,6S)-5a (0.5 g, 2.24 mmol; ‰ꢀŠ2D5=±6.3 (c=1, MeOH); ee=99%) as a pale-
yellow oil, together with the unreacted alcohol (1S,6R)-5b (0.25 g, 1.63 mmol; ‰ꢀŠ2D5=±46.1 (c=1,
MeOH); mp 72±75ꢀC; ee=97%). 1H NMR (400 MHz, CDCl3) ꢁ (ppm) for 5a: 0.95 (3H, t, CH3,
J=7.4), 1.63±1.68 (2H, m, CH2CH2CH3), 2.16±2.20 (2H, m, H-2a and H-5a), 2.31 (2H, t,
CH2CH2CH3 J=7.4), 2.44±2.58 (2H, m, H-2b and H-5b), 3.38±3.41 (1H, m, H-1), 4.02±4.04 (1H,
m, H-6), 5.04 (1H, d, CH2OCOPr, J=11.3), 5.12 (1H, d, CH2OCOPr, J=11.4), 5.29±5.85 (2H,
m, CHCH). Anal. calcd for C12H17NO3: C, 64.55; H, 7.67; N, 6.27; found: C, 64.63; H, 7.61; N,
6.35.
1
The H NMR (400 MHz, CDCl3) ꢁ (ppm) data for 5b are similar to those for (þ)-5. Anal.
calcd for C8H11NO2: C, 62.73; H, 7.24; N, 9.14; found: C, 62.65; H, 7.16; N, 9.21.
3.8. Gram-scale resolution of 6
With the procedure described above, the reaction of racemic 6 (1 g, 6.53 mmol) and vinyl
butyrate (1.48 g, 13.06 mmol) in dry acetone (65 ml) in the presence of lipase PS (3.25 g) for 6 h
a€orded the ester (1R,6S)-6a (0.49 g, 2.21 mmol; ‰ꢀŠ2D5=±43.3 (c=0.5, CHCl3); ee=99%) as a
pale-yellow oil, together with the unreacted alcohol (1S,6R)-6b (0.32 g, 2,09 mmol; ‰ꢀŠ2D5=±9.5
(c=1.88, MeOH); ee=94%) as a colourless oil. 1H NMR (400 MHz, CDCl3) ꢁ (ppm) for 6a: 0.95
(3H, t, CH3, J=7.4), 1.56±2.15 (6H, m, 2ÂCH2 and CH2CH2CH3), 2.30 (2H, t, CH2CH2CH3,
J=7.5), 3.48±3.51 (1H, m, H-1), 4.11 (1H, t, H-6, J=4.9), 5.00 (1H, d, CH2OCOPr, J=11.2), 5.16
(1H, d, CH2OCOPr, J=11.2), 6.02±6.21 (2H, m, CHCH). Anal. calcd for C12H17NO3: C, 64.55;
1
H, 7.67; N, 6.27; found: C, 64.72; H, 7.81; N, 6.33. The H NMR (400 MHz, CDCl3) ꢁ (ppm)
data for 6b are similar to those for (þ)-6. Anal. calcd for C8H11NO2: C, 62.73; H, 7.24; N, 9.14;
found: C, 62.61; H, 7.32; N, 9.23.
3.9. Acid hydrolysis of 4a and 4b
(1R,6S)-4a (0.3 g, 1.33 mmol) was dissolved in 18% HCl (6 ml) and re¯uxed for 2 h at 70ꢀC.
The solvent was evaporated o€, the residue was puri®ed by ion-exchange chromatography and
the product was recrystallized from ethanol, which a€orded white crystals of (1R,2S)-4c (0.07 g,

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Â
1599
0.39 mmol; ‰ꢀŠ2D5=±19.6 (c=0.25, H2O); mp 229±230ꢀC; ee=98%). 1H NMR (400 MHz, D2O) ꢁ
(ppm) for 4c: 1.39±1.95 (8H, m, 4ÂCH2), 2.62±2.66 (1H, m, H-1), 3.45±3.49 (1H, m, H-2). Anal.
calcd for C7H13NO2: C, 64.55; H, 7.67; N, 6.27; found: C, 64.31; H, 7.51; N, 6.39.
Similarly, (1S,6R)-4b (0.2 g, 1.29 mmol) a€orded white crystals of (1S,2R)-4d (0.1 g, 0.56
mmol; ‰ꢀŠ2D5=+20 (c=0.25, H2O); mp 230±231ꢀC; ee=97%).
The 1H NMR (400 MHz, D2O) ꢁ (ppm) data for 4d are similar to those for 4c. Anal. found: C,
64.25; H, 7.43; N, 6.15.
3.10. Acid hydrolysis of 5a and 5b
Similarly, (1R,6S)-5a (0.2 g, 0.89 mmol) a€orded white crystals of (1R,2S)-5c (69 mg, 0.39 mmol;
‰ꢀŠ2D5=±36.2 (c=0.5, H2O); mp 224±225ꢀC; ee=99%). 1H NMR (400 MHz, D2O) ꢁ (ppm) for 5c:
2.16±2.44 (4H, m, 2ÂCH2), 2.67±2.71 (1H, m, H-1), 3.69±3.73 (1H, m, H-2), 5.57±5.76 (2H, m,
CHCH). Anal. calcd for C7H11NO2: C, 59.56; H, 7.85; N, 9.92; found: C, 59.28; H, 7.78; N, 9.81.
Similarly, (1S,6R)-5b (0.15 g, 0.98 mmol) a€orded white crystals of (1S,2R)-5d (45 mg, 0.32
mmol; ‰ꢀŠ2D5=+34 (c=0.27, H2O); mp 223±226ꢀC; ee=97%); lit.21 ‰ꢀŠD25=+36.4 (c=0.45, H2O).
The 1H NMR (400 MHz, D2O) ꢁ (ppm) data for 5d are similar to those for 5c. Anal. found: C,
59.73; H, 7.83; N, 9.75.
3.11. Acid hydrolysis of 6a and 6b
Similarly, (1R,6S)-6a (0.2 g, 0.89 mmol) a€orded white crystals of (1R,2S)-6c (48 mg, 0.34
25
mmol; ‰ꢀŠD =+120 (c=0.25, H2O); mp 220±221ꢀC; ee=99%). H NMR (400 MHz, D2O) ꢁ
(ppm) for 6c: 1.80±2.19 (4H, m, 2ÂCH2), 2.72±2.77 (1H, m, H-1), 3.95±4.03 (1H, m, H-2), 5.71±
6.14 (2H, m, CHCH). Anal. calcd for C7H11NO2: C, 59.56; H, 7.85; N, 9.92; found: C, 59.68; H,
7.96; N, 9.81.
1
Similarly, (1S,6R)-6b (0.25 g, 1.63 mmol) a€orded white crystals of (1S,2R)-6d (80 mg, 0.56
mmol; ‰ꢀŠ2D5=^122 (c=0.25, H2O); mp 217±218ꢀC; ee=99%).
The 1H NMR (400 MHz, D2O) ꢁ (ppm) data for 6d are similar to those for 6c. Anal. found: C,
59.40; H, 7.63; N, 9.98.
3.12. Preparation of enantiomerically pure b-lactams 4e±6e
(1S,6R)-4b (0.1 g, 0.64 mmol) was dissolved in methanol (10 ml), NH4OH (1 ml) was added
and the mixture was stirred at room temperature for 13 h. The solution was evaporated, the
residue was chromatographed on silica, and elution with dichloromethane:ethyl acetate (1:1)
a€orded white crystals of (1S,6R)-4e (65 mg, 0.52 mmol; ‰ꢀŠ2D5=±3.8 (c=0.27, CHCl3); mp 69±
71ꢀC; ee=98%).
1H NMR (400 MHz, CDCl3) ꢁ (ppm) for 4e: 1.46±1.86 (8H, m, 4ÂCH2), 3.22±3.23 (1H, m, H-
1), 3.83±3.86 (1H, m, H-6), 6 (1H, br). Anal. calcd for C7H11NO: C, 67.17; H, 8.86; N, 11.19;
found: C, 67.35; H, 8.62; N, 11.32.
Similarly, (1S,6R)-5b (50 mg, 0.33 mmol) a€orded white crystals of (1S,6R)-5e (32 mg, 0.26
mmol; ‰ꢀŠ2D5=±26.3 (c=0.50, CHCl3); mp 152±153ꢀC; ee=98%); lit.21 ‰ꢀŠ2D5=±28.6 (c=0.585,
CHCl3). 1H NMR (400 MHz, D2O) ꢁ (ppm) for 5e: 2.12±2.22 (2H, m, H-2a and H-5a), 2.32±2.51
(2H, m, H±2b and H-5b), 3.42±3.45 (1H, m, H-1), 4.06±4.09 (1H, m, H-6), 5.81±5.89 (2H, m,
CHCH). Anal. calcd for C7H9NO: C, 68.27; H, 7.37; N, 11.37; found: C, 68.45; H, 7.18; N, 11.23.

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1600
Similarly, (1S,6R)-6b (50 mg, 0.33 mmol) a€orded white crystals of (1S,6R)-6e (27 mg, 0.22
25
ꢀ
1
mmol; ‰ꢀŠD =+164 (c=0.13, CHCl3); mp 106±108 C; ee=94%). H NMR (400 MHz, CDCl3) ꢁ
(ppm) for 6e: 1.59±2.12 (4H, m, 2ÂCH2), 3.48±3.56 (1H, m, H-1), 4.03 (1H, t, H-6, J=4.78), 5.82
(1H, br), 5.94±6.17 (2H, m, CHCH). Anal. calcd for C7H9NO: C, 68.27; H, 7.37; N, 11.37; found:
C, 68.03; H, 7.25; N, 11.48.
Acknowledgements
The authors' thanks are due to OTKA (grant No. T 030452) and MKM (grant No. FKFP
0535/1999) for ®nancial support.
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