Chemoenzymatic synthesis of optically active 2-phenyl-2-(1H-1,2,4- triazol-1-ylmethyl)hexanenitrile

Article abstract of DOI:10.1016/S0040-4020(00)00031-4

(±)-2-Cyano-2-phenyl-1-hexanol 3 was resolved to each enantiomer using Candida rugosa and Pseudomonas fluorescens lipases in 62 and 99% ee, respectively. The absolute stereochemistry of one of the enantiomers was determined to be (S) by diastereomeric ami

Full text of DOI:10.1016/S0040-4020(00)00031-4

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 1309–1314
Chemoenzymatic Synthesis of Optically Active
2-Phenyl-2-(1H-1,2,4-triazol-1-ylmethyl)hexanenitrile
b
a
c
Dai Sig Im,a Chan Seong Cheong,b, So Ha Lee, Byoung Hee Youn and Seok Chan Kim
*
aDepartment of Chemistry, Yonsei University, Shin chon 134, Seoul 120-749, South Korea
bLife Sciences Division, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 130-650, South Korea
cDepartment of Chemistry, Kook min University, Chongnungdong, Seoul 136-702, South Korea
Received 22 November 1999; accepted 6 January 2000
Abstract—(^)-2-Cyano-2-phenyl-1-hexanol 3 was resolved to each enantiomer using Candida rugosa and Pseudomonas fluorescens
lipases in 62 and 99% ee, respectively. The absolute stereochemistry of one of the enantiomers was determined to be (S) by diastereomeric
amide formation and X-ray crystallography. The resolved alcohols of (R)- and (S)-isomer were transformed to Systhane᭨ analogues. ᭧ 2000
Elsevier Science Ltd. All rights reserved.
2-p-Chlorophenyl-2-(1H-1,2,4-triazol-1-ylmethyl)hexane-
nitrile 1 (Systhane᭨) is a systemic fungicide which inhibits
ergosterol biosynthesis.1 The stereochemistry of the sterol
biosynthesis inhibitors, particularly of the azoles and
amines, can often have a decisive influence upon biological
activity. The question concerning the influence of stereo-
chemistry upon biological activity is therefore of particular
interest in this class. For fungicidal examples, with triadi-
menol the biological activity of the threo diastereomer is
higher than that of the erythro diastereomer.2 In the case of
dichlobutrazole, the enantiomers (1R, 2R) and (1S, 2S) are
much more active than their diastereomers (1S, 2R) and (1R,
2S) in an S8 yeast enzyme system (Fig. 1).3
Systhane᭨ 1 is commercially available for crop protection
as a racemate and has one quaternary chiral carbon. To date,
there are no reports that resolve it to a single isomer and
compare the biological activities between the two
enantiomers. Thus we do not know which enantiomer is
more active biologically. We have been interested in
compound 1 with a view to separating the two enantiomers
Figure 1. Diastereomeric pairs biological activity.
and testing their biological activities. To resolve them, we
Figure 2. Retrosynthesis of Systhane᭨.
Keywords: chemoenzymatic; fungicide; quaternary carbon; lipase-catalyzed reaction.
* Corresponding author. Tel.: ϩ82-02-958-5153; fax: ϩ82-02-958-5189; e-mail: c2496@kistmail.kist.re.kr
0040–4020/00/$ - see front matter ᭧ 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00031-4

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D. S. Im et al. / Tetrahedron 56 (2000) 1309–1314
Scheme 1. Lipase-catalyzed reaction of compound 3.
used lipase which is a useful catalyst for the preparation of
enantiomerically pure compounds4 (Fig. 2).
of compound 1. It can be transformed to compound 1 and
other related compounds by chemical modifications such as
aromatic chlorination, nitration and alkylation. We selected
two kinds of lipase, Pseudomonas fluorescens and Candida
rugosa which resolved them moderately. We report here the
results of the resolution and structural determination of
compound 3 (Scheme 1).
In a lipase-catalyzed reaction, it is important to select a
proper substrate. By screening several lipases for resolving
compound 2, we did not find promising ones. Thus we synthe-
sized compound 3 as the intermediate for the preparation
Table 1. Resolutions of compound 3 using Candida rugosa and Pseudomonas fluorescens
Lipase
Reaction time (h)
Conversion (%)
Ee (%)
E
Alcohol
Acetate
Candida rugosa (CRL)
Pseudomonas fluorescens
(PFL)a
1
24
30
40
26 (S)
50 (R)
62 (R)
76 (S)
5.5
11
Pseudomonas fluorescens
48
22
28 (R)
99 (S)
Ͼ200
(Amano AK)b
a Pseudomonas fluorescens lipase from Aldrich Co.
b Pseudomonas fluorescens lipase from Amano Pharmaceutical Co.
Scheme 2. Synthesis of compounds 9 and 11.

D. S. Im et al. / Tetrahedron 56 (2000) 1309–1314
1311
Scheme 3. Synthesis of N-[(R)-a-methylbenzyl]-(2S)-cyano-2-phenylhexanamide 6.
Compound 3 was prepared by conventional methods.5 We
resolved it using C. rugosa and P. fluorescens lipases
because of their effectiveness among several lipases in
the previous report.6 The reaction was proceeded by trans-
esterification of the substrate with vinyl acetate in the
presence of lipase at 32–34ЊC and the solvent was
n-hexane.7 As shown in Table 1, the faster reacting enantio-
mer with C. rugosa and P. fluorescens lipase was found to
be (R) and (S)-one, respectively. Surprisingly, the resolving
efficiency between two kinds of P. fluorescens lipase
was different although they are derived from the same
species.
But the faster reacting enantiomer was the same as (S)-enan-
tiomer. The enantioselectivity (E)8 using P. fluorescens
lipase from Amano Pharmaceutical Co. was up to 200 and
we could obtain the enantiomerically pure (S)-enantiomer.
When C. rugosa lipase was used, we got the (R)-enantiomer
in 62% ee. Thus we adopted a strategy such as product
recycling9 to enhance its ee value. Two further enzymatic
resolutions of the compound 3 derived from the first
resolved (R)-acetate produced the (R)-enantiomer in up to
99% ee. Each enantiomer was mesylated and displaced by
triazole sodium salt by the general method as described in
Scheme 2.
Next, we attempted to crystallize diastereomeric derivatives
as follows: (i) esterification of the alcohol 3 with (1R)-(Ϫ)-
camphorsulfonyl chloride and (S)-(ϩ)-mandelic acid,
respectively; (ii) esterification of the acid 4 with alcohols
such as (Ϫ)-menthol and (ϩ)-cinchonine; (iii) diastereo-
meric salts of the acid 4 with l -quinine. All of the trials
failed to crystallize the diastereomeric derivatives for deter-
mining the absolute stereochemistry of compound 3. Thus
we derivatized carboxylic acid 4 to its diastereomeric amide
as described in Scheme 3. The diastereomeric amide of (^)-
acid 4 and (R)-(ϩ)-a-methylbenzylamine easily crystallized
in methanol and one of the diastereomeric pairs was
submitted to X-ray crystallographic analysis. Its absolute
stereochemistry was the (1R,2S)-amide 6. It was identical
to the amide which resulted from the reaction of (R)-(ϩ)-a-
methylbenzylamine with the acid of the (S)-alcohol 3, which
was resolved by C. rugosa lipase. From these results, we
determined the stereochemistry of each enantiomer derived
from compound 3.
In summary, (^)-2-cyano-2-phenyl-1-hexanol
3 was
resolved to (S)-enantiomer with up to 99% ee using
P. fluorescens lipase (Amano AK) and to (R)-enantiomer
with up to 98% ee by three times recycling enzymatic
reactions using C. rugosa lipase. The absolute stereo-
chemistry of each enantiomer was determined by X-ray
crystallography (Fig. 3).
Figure 3. Molecular structure of N-[(R)-a-methyl benzyl]-(2S)-2-cyano-2-
phenylhexanamide 6.
Each enantiomer of the Systhane᭨ analogue (phenyl without

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D. S. Im et al. / Tetrahedron 56 (2000) 1309–1314
chloride) was synthesized and submitted to testing for fungi-
cidal activities of both enantiomers. We will continue to
synthesize Systhane᭨ by chlorination of each enantiomer
of the aromatic compound 3 and study the differences of
biological activity between them. Furthermore, after synthe-
sizing other related analogues, we will study the different
biological activities between each enantiomer.
(n-hexane/ethyl acetate, 9:1); GC/MSD retention time
(min) 7.24, (m/z) 51, 57, 65, 77, 89, 103, 117 (100), 130,
145, 158, 173 (Mϩ); IR (neat) 3120, 2958, 2240, 1456,
1380 cmϪ1
;
1H NMR (250 MHz, CDCl3) d 0.90 (t,
Jˆ8.5 Hz, 3H), 1.33–1.47 (m, 4H), 1.86–1.97 (m, 2H),
3.76 (dd, Jˆ8.0, 10.0 Hz, 1H), 7.28–7.40 (m, 5H); 13C
NMR (63 MHz, CDCl3) d 14.1, 22.5, 29.5, 36.0, 37.8,
121.3, 127.6, 128.3, 129.4, 136.4; Anal. Calcd for
C12H15N: C, 83.19; H, 8.73; N, 8.08. Found: C, 83.15; H,
8.75; N, 8.03.
Experimental
General
To a stirred suspension of sodium hydride (5.82 g,
145 mmol, 60% dispersion in mineral oil) in dry DMF
(150 mL) was added dropwise 1-cyano-1-phenylpentane
(21.0 g, 121 mmol) for 30 min at 0ЊC, paraformaldehyde
(8 g, 5 equiv.) was added in several portions at 0ЊC. After
the complete addition, the mixture was warmed to room
temperature and stirred overnight. The reaction medium
was quenched with cold ice water (300 mL) and extracted
with diethyl ether (3×50 mL). The combined organic
extracts were washed with saturated aqueous NaHCO3 solu-
tion, brine, dried over MgSO4 and concentrated to furnish
26.5 g of crude 3. Silica gel column chromatography
(n-hexane/ethyl acetate, 4:1) provided 21.0 g (85.4%) as a
clear oil. Rf 0.56 (n-hexane/ethyl acetate, 2:1); GC/MSD
retention time (min) 8.80, (m/z) 51, 63, 77, 91, 103, 117,
130, 145, 158, 173 (100), 184 (MϩϪ18); IR (neat) 3502,
1H NMR (250 or 300 MHz) and 13C NMR spectra (63 or
75 MHz) were recorded on a Varian Gemini 250 or
300 MHz spectrometer with TMS as an internal reference.
IR spectra were recorded on a MIDAC 101025 FT-IR spec-
trometer and optical rotation was measured on Autopol᭨ III
polarimeter (Rudolph Research Co.). Low EI resolution
mass spectra were determined on HP GC 5972 [Column:
Hewlett-Packard fused silica capillary column HP-5 cross-
linked 5% Phenyl methyl silicone, Column ID 0.20 mm,
Film thickness: 0.11 mm, Length: 25 m, Detector: Mass
selective detector, 280ЊC, Injector 280ЊC, Program: Ini.
temp. 70ЊC (2 min), 20ЊC/min, Final temp. 300ЊC
(20 min)] and HP MS 5988A system at 70 eV. Analytical
chiral GLC work was carried out on a Hewlett Packard 5890
௣
3122, 2958, 2240, 1456, 1381, 1064 cmϪ1 1H NMR
;
Series II Gas Chromatograph [Column: Beta-DEX 110,
Fused silica capillary column, Column ID 0.25 mm, Film
thickness: 0.25 mm, Length: 30 m, Detector: FID 250ЊC,
Injector 250ЊC, Program: Ini. temp. 140ЊC (40 min), 2ЊC/min,
Final temp. 200ЊC (10 min)].
(250 MHz, CDCl3) d 0.86 (t, Jˆ8.6 Hz, 3H), 1.10–1.59
(m, 4H), 1.80–2.15 (m, 2H), 1.91 (br s, 1H), 3.89 (s, 2H),
7.34–7.46 (m, 5H); 13C NMR (63 MHz, CDCl3) d 14.1,
23.0, 27.4, 35.7, 51.5, 69.8, 122.0, 126.8, 128.6, 129.5,
136.2; Anal. Calcd for C13H17NO: C, 76.81; H, 8.43; N,
6.89. Found: C, 76.65; H, 8.47; N, 6.85.
Materials
Synthesis of acetate of (^)-2-cyano-2-phenyl-1-hexanol
(3). To a solution of (^)-3 (4.4 g, 21.7 mmol) in anhydrous
methylene chloride (20 mL) was added a trace of
4-(dimethylamino)pyridine as catalyst, excess pyridine
(5 mL) and acetic anhydride (10 mL). After the mixture
was stirred for 2 h at room temperature, and poured into
cold 10% aqueous HCl solution (30 mL), and extracted
with diethyl ether (2×20 mL). The combined organic
extracts were washed saturated aqueous NaHCO3 solution,
brine, dried over MgSO4 and concentrated to furnish 5.1 g
of crude acetyl ester. Silica gel column chromatography
(n-hexane/ethyl acetate, 10:1) provided 4.94 g (93%) of
(^)-2-cyano-2-phenylhexyl acetate as a clear oil. Rf 0.38
(n-hexane/ethyl acetate, 4:1); GC/MSD retention time
(min) 9.23, (m/z) 51, 63, 77, 91, 103, 166, 130, 145, 158,
173 (100), 186, 215, 245 (Mϩ); IR (neat) 3120, 2958, 2242,
All reactions were carried out under an atmosphere of nitro-
gen. Column chromatography was performed on Merck
Silica Gel 60 (230–400 mesh). TLC was carried out using
glass sheets precoated with silica gel 60 F254 prepared by E.
Merck. All the commercially available reagents were
obtained from Aldrich, Fluka and Tokyo Kasei Chemical
Company, and generally used without further purification.
Solvents were distilled over appropriate drying materials
before use. Lipase AK (P. fluorescens, Ͼ20000 u/g) was
obtained from Amano Pharmaceutical Company. CRL (C.
rugosa, 860 u/mg) and PFL (P. fluorescens, 42.5 u/mg)
were obtained from Sigma and Aldrich Company, respec-
tively.
Synthesis of (^)-2-cyano-2-phenyl-1-hexanol (3).5 To a
stirred suspension of sodium hydride (6.1 g, 170 mmol,
60% dispersion in mineral oil) in dry DMF (100 mL) was
added dropwise benzyl cyanide (17.6 g, 150 mmol) for
30 min at 0ЊC. After the mixture was stirred for 30 min,
1-bromobutane (20.5 g, 150 mmol) was added at 15ЊC for
12 h. The reaction medium was quenched with cold ice
water (200 mL) and extracted with diethyl ether
(3×50 mL). The combined organic extracts were washed
with saturated aqueous NaHCO3 solution, brine, dried
over MgSO4 and concentrated to furnish 30 g of crude
1-cyano-1-phenylpentane. Silica gel column chroma-
tography (n-hexane/ethyl acetate, 10:1) provided 21.3 g
(82%) of 1-cyano-1-phenylpentane as a clear oil. Rf 0.33
1
1748, 1454, 1380, 1224, 1048 cmϪ1; H NMR (250 MHz,
CDCl3) d 0.86 (t, Jˆ8.8 Hz, 3H), 1.12–1.50 (m, 4H),
1.8–1.95 (m, 2H), 2.06 (s, 3H), 4.36 (s, 2H), 7.33–
7.45(m, 5H); 13H NMR (63 MHz, CDCl3) d 13.5, 20.3,
22.2, 26.6, 35.8, 47.8, 68.3, 120.4, 126.0, 128.1, 128.5,
135.1, 169.9; Anal. Calcd for C15H19NO2: C, 73.44; H,
7.81; N, 5.71. Found: C, 73.42; H, 7.81; N, 5.58.
Kinetic resolution of (^)-2-cyano-2-phenyl-1-hexanol (3)
using P. fluorescens lipase (Amano AK)
To a stirred solution of compound 3 (210 mg, 1.03 mmol) in

D. S. Im et al. / Tetrahedron 56 (2000) 1309–1314
1313
1
anhydrous n-hexane/ethyl acetate (9:1, 10 mL) was added
Amano AK (210 mg) and vinyl acetate (89 mg, 1.03 mmol)
at 32–34ЊC. After stirring for 48 h, GC analysis showed a
conversion of 22%. From the reaction mixture, the enzyme
was removed by filtration and washed with diethyl ether
(3×10 mL). The combined organic layer was concentrated
to afford an oily residue, which was chromatographed on
silica-gel column with n-hexane/ethyl acetate (4:1) to give
the acetate of (S)-3 and unreacted alcohol (R)-3. The
isolated acetate of (S)-3 was hydrolyzed with 1.2N metha-
nolic KOH solution to afford the corresponding alcohol
(S)-3. [a]2D6ˆϪ11.02 (c 0.58, methanol). Retention time
2244, 1462, 1364, 1176, 956 cmϪ1; H NMR (300 MHz,
CDCl3) d 0.83 (t, Jˆ7.3 Hz, 3H), 1.20–1.55 (m, 4H),
1.87–2.17 (m, 2H), 2.91 (s, 3H), 4.43 (s, 2H), 7.24–7.47
(m, 5H); 13C NMR (75 MHz, CDCl3) d 14.1, 22.8, 27.1,
35.9, 38.1, 48.7, 73.2, 120.3, 126.7, 129.2, 129.7, 134.6;
Calcd for C14H19NO3S: C, 59.76; H, 6.81; N, 4.98. Found:
C, 59.70; H, 6.86; N, 4.87.
To a solution of mesylated 8 (57 mg, 0.20 mmol) in DMSO
(3 mL) was added 1,2,4-triazole sodium derivative (91 mg,
1 mmol). The mixture was heated at 105ЊC for 10 h, then
cooled to room temperature and partitioned between methy-
lene chloride and water. The organic layer was concentrated
to furnish crude triazole derivative 9 (60 mg). Purification
by silica gel column chromatography (n-hexane/ethyl ace-
tate, 2:1) provided 46 mg (90%) as a clear oil. Rf 0.28 (n-
hexane/ethyl acetate, 1:1); [a]3D1ˆϩ60.9 (c 0.55, methanol);
GC/MSD retention time 10.71 min, (m/z) 55, 63, 82, 91,
103, 116, 145 (100), 172, 185, 195, 211, 225, 239, 254
(Mϩ); IR (neat) 3122, 2956, 2872, 2240, 1508, 1450,
௣
(min) of (S)-(Ϫ)-3 was 54.88 from Beta DEX chiral
column. The enantiomeric excess of reacted alcohol (S)-3
and unreacted alcohol (R)-3 were 99 and 28%, respectively.
Kinetic resolution of (^)-2-cyano-2-phenyl-1-hexanol (3)
using P. fluorescens lipase (PFL)
To a stirred solution of compound 3 (210 mg, 1.03 mmol) in
anhydrous n-hexane/ethyl acetate (9:1, 10 mL) was added
PFL (210 mg) and vinyl acetate (89 mg, 1.03 mmol) at
32–34ЊC. After stirring for 24 h, GC analysis showed a
conversion of 40%. By the same procedure as above, the
enantiomeric excess of reacted alcohol (S)-3 and unreacted
alcohol (R)-3 were obtained in 76 and 50%, respectively.
1350, 1274, 1208, 1138 cmϪ1
;
1H NMR (300 MHz,
CDCl3) d 0.83 (t, Jˆ7.2 Hz, 3H), 1.28–1.53 (m, 4H),
1.84–2.23 (m, 2H), 4.50 (d, Jˆ14.2 Hz, 1H), 4.66 (d,
Jˆ14.2 Hz, 1H), 7.28–7.42 (m, 5H), 7.77 (s, 1H), 7.89 (s,
1H); 13C NMR (75 MHz, CDCl3) d 14.3, 23.1, 27.5, 35.7,
51.6, 58.2, 122.2, 126.7, 128.5, 129.4, 136.4, 144.6, 152.2;
Anal. Calcd for C15H18N4: C, 70.84; H, 7.13; N, 22.03.
Found: C, 70.55; H, 7.23; N, 21.50.
Kinetic resolution of (^)-2-cyano-2-phenyl-1-hexanol (3)
using C. rugosa lipase (CRL)
Synthesis of (S)-(Ϫ)-2-phenyl-2-(1H-1,2,4-triazol-1-yl-
methyl)hexanenitrile (11). Under the same procedures as
above, enantiopure triazole derivative (S)-11 was obtained
in 92% yield. [a]3D1ˆϪ61.4 (c 0.55, methanol).
To a stirred solution of compound 3 (102 mg, 0.50 mmol) in
anhydrous n-hexane/ethyl acetate (9:1, 10 mL) was added
CRL (100 mg) and vinyl acetate (43 mg, 0.50 mmol) at
32–34ЊC. After stirring for 1 h, GC analysis showed a
conversion of 30%. By the same procedure as above, the
enantiomeric excess of reacted alcohol (R)-3 and unreacted
alcohol (S)-3 were obtained in 62 and 26%, respectively.
Synthesis of (^)-2-cyano-2-phenylhexanoic acid (4). To a
solution of (^)-3 (0.8 g, 3.94 mmol) in acetone (10 mL)
was added Jones reagent (1N aqueous H2SO4 solution,
6 mL) at 0ЊC. After stirring for 3 h at room temperature,
the reaction mixture was quenched with cold ice water
(20 mL) and extracted with diethyl ether (2×20 mL). The
combined organic extracts was washed with water, dried
over MgSO4 and concentrated to furnish 710 mg of crude
(^)-acid 4 as a viscous oil. This acid was used without
further purification in the next step. Rf 0.45 (ethyl acetate/
methanol, 1:1); GC/MSD retention time (min) 4.15, (m/z)
57, 63, 77, 89, 103, 117 (100), 130, 144, 156, 173 (MϩϪ44);
IR (neat) 3480, 3122, 2962, 2870, 2254, 1716, 1452, 1380,
Product recycling using C. rugosa lipase (CRL)
The first resolved alcohol (R)-3 was used for enzyme
reaction using the same lipase under the above condition.
The (R)-enantiomer was obtained in 62% ee and by third
recycling, it was up to 98% ee. [a]2D6ˆϩ11.05 (c 0.58,
methanol), retention time (min) of (R)-(ϩ)-3 was 54.21
௣
from Beta DEX chiral column.
;
1216 cmϪ1 1H NMR (300 MHz, CDCl3) d 0.86 (t,
Synthesis of (R)-(ϩ)-2-phenyl-2-(1H-1,2,4-triazol-1-yl-
methyl)hexanenitrile (9). To a solution of (S)-3 alcohol
(44 mg, 0.23 mmol) in anhydrous methylene chloride
(3 mL) were added triethylamine (61 mL, 0.44 mmol) and
methanesulfonyl chloride (34 mL, 0.44 mmol). After the
reaction mixture was stirred for 3 h at 0ЊC, the reaction
was quenched with saturated aqueous NaHCO3 solution
(20 mL). The organic layer separated from the reaction
mixture was washed with saturated aqueous NaHCO3 solu-
tion (2×10 mL), 5% aqueous HCl solution and H2O, dried
over MgSO4 and concentrated to furnish 150 mg of crude
mesylated 8. Silica gel column chromatography (n-hexane/
ethyl acetate, 4:1) provided 57.6 mg (89%) as a clear oil. Rf
0.61 (benzene/ethyl acetate, 5:1); GC/MSD retention time
(min) 10.91, (m/z) 51, 65, 79, 103, 116, 129, 145, 172 (100),
185, 202, 224, 238, 251, 281 (Mϩ); IR (neat) 3124, 2958,
Jˆ6.8 Hz, 3H), 1.20–1.41 (m, 4H), 2.01–2.10 (m, 1H),
2.17–2.23 (m, 1H), 7.30–7.37 (m, 3H), 7.50–7.55 (m,
2H), 10.40 (s, 1H); 13C NMR (75 MHz, CDCl3) d 14.1,
22.7, 27.8, 37.8, 55.5, 119.3, 126.5, 129.1, 129.4, 134.7,
173.2; Anal. Calcd for C13H15NO2: C, 71.87; H, 6.96; N,
6.45. Found: C, 69.60; H, 6.97; N, 6.03.
Synthesis of N-[(R)-a-methylbenzyl]-2-cyano-2-phenyl-
hexanamide (5). To a stirred solution of crude (^)-acid 4
(300 mg, 1.38 mmol) in anhydrous methylene chloride
(3 mL) and dimethylformamide (3 mL) was added 3-hy-
droxy-1,2,3-benzotriazin-4(3H)-one (270 mg, 1.66 mmol)
and DCC (341 mg, 1.66 mmol) at 0ЊC. After the mixture
was stirred for 30 min, (R)-(ϩ)-a-methylbenzylamine
(201 mg, 1.66 mmol) was added at 0ЊC. After the mixture

1314
D. S. Im et al. / Tetrahedron 56 (2000) 1309–1314
was stirred for 3 h at room temperature, ethyl acetate
(20 mL) was added. After removing the white solid by fil-
tering, the filtrate was washed with saturated aqueous
NaHCO3 solution, brine, dried over MgSO4 and concen-
trated to furnish 600 mg of crude 5 as diastereomeric
mixtures. Silica gel column chromatography (n-hexane/
ethyl acetate, 10:1) provided 380 mg (86%) of diastereo-
meric amide as a white solid. The recrystallization of
compound 5 from methanol gave N-[(R)-a-methylbenzyl]-
(2S)-cyano-2-phenylhexanamide 6 (70 mg); mp 100–
103ЊC; Rf 0.49 (n-hexane/ethyl acetate, 2:1); [a]2D0ˆϩ25.1
(c 0.15, methanol); GC/MSD retention time (min) 12.22,
(m/z) 51, 77, 91, 105 (100), 130, 145, 173, 190, 201, 215,
248, 277, 305, 320 (Mϩ); IR (KBr) 3370, 3150, 2964, 2932,
an Enraf-Nonius CAD4 automated diffractometer equipped
with a Mo X-ray tube and a graphite crystal monochro-
mator; crystal data for (1R,2S)-6: C21H24N2O, Mˆ320.42,
monoclinic, C2 (#5), aˆ20.003 (4), bˆ8.612 (4), cˆ11.063
3
˚
˚
(2) A, aˆ90, bˆ99.97 (2), gˆ90, Vˆ876.9 (9) A , Zˆ4,
Dcˆ1.134 g cmϪ3
,
F(000)ˆ688. Final
R
indices:
R1ˆ0.0588, wR2ˆ0.1440.
Acknowledgements
We are grateful to the Korea Institute of Science and Tech-
nology for financial support and Dr Kwan Mook Kim for X-
ray crystallographic analysis.
1
2868, 2238, 1686, 1652, 1526, 1450, 1250 cmϪ1; H NMR
(300 MHz, CDCl3) d 0.84 (t, Jˆ3.6 Hz, 3H), 1.25 (m, 4H),
1.37 (d, Jˆ11.1 Hz, 3H), 2.06 (m, 1H), 2.38 (m, 1H), 5.04
(m, 1H), 6.38 (d, Jˆ7.4 Hz, 1H), 7.26–7.60 (m, 10H); 13C
NMR (75 MHz, CDCl3) d 14.1, 21.9, 22.1, 28.0, 38.3, 50.5,
54.8, 120.7, 126.3, 126.4, 128.0, 129.1, 129.2, 129.5, 135.9,
142.7, 165.9; Anal. Calcd for C21H24N2O: C, 78.71; H, 7.55;
N, 8.74. Found: C, 78.90; H, 7.61; N, 8.78.
References
1. Haug, G.; Hoffmann Chemistry of Plant Protection—Sterol
Biosynthesis, Inhibitors and Antifeeding Compounds; Springer:
Berlin, 1986, p 25.
N-[(R)-a-methylbenzyl]-(2R)-cyano-2-phenylhexanamide
7. Mp 71–74ЊC; Rf 0.52 (n-hexane/ethyl acetate, 2:1);
[a]2D0ˆϪ17.7 (c 0.15, methanol); GC/MSD retention time
(min) 12.08, (m/z) 51, 77, 91, 105 (100), 130, 145, 173, 190,
201, 215, 249, 264, 277, 305, 320 (Mϩ); IR (KBr) 3312,
3122, 2964, 2932, 2870, 2240, 1684, 1652, 1528, 1450,
2. Kramer, W.; Buchel, K. H.; Draber, W. Pesticide Chemistry.
Human Welfare and the Environment 1983, 1, 223.
3. Baldwin, B. C.; Wiggins, T. E. Pestic. Sci. 1984, 15, 156.
4. (a) Brieva, R.; Crich, J. Z.; Sih, C. J. J. Org. Chem. 1993, 58,
1068. (b) Hallinan, K. O.; Honda, T. Tetrahedron 1995, 51, 12211.
(c) Fadel, A.; Arzel, P. Tetrahedron: Asymmetry 1995, 6, 893. (d)
Shiotani, S.; Okada, H.; Nakamata, K.; Yamamoto, T.; Sekino, F.
Heterocycles 1996, 43, 1031.
5. Miller, G. A.; Carley, H. E.; Chan, H. F. DOS 2 604 047, 1976,
Rohm and Haas Company.
6. Cheong, C. S.; Im, D. S.; Kim, J. Y.; Kim, I. O. Biotechnol. Lett.
1996, 18, 1419.
1250 cmϪ1
;
1H NMR (300 MHz, CDCl3) d 0.90 (t,
Jˆ3.6 Hz, 3H), 1.25 (m, 4H), 1.37 (d, Jˆ11.1 Hz, 3H),
2.06 (m, 1H), 2.38 (m, 1H), 5.04 (m, 1H), 6.35 (d,
Jˆ7.3 Hz, 1H), 7.26–7.60 (m, 10H); 13C NMR (75 MHz,
CDCl3) d 14.1, 22.1, 22.7, 28.0, 37.9, 50.4, 54.8, 120.7,
126.1, 126.4, 127.8, 129.0, 129.2, 129.5, 135.8, 142.5,
165.7.
7. Each enzyme was used as mass equivalent to substrate.
8. Chen, C. S.; Fugimoto, Y.; Girdaukas, G.; Sih, C. J. J. Am.
Chem. Soc. 1982, 104, 7294.
X-Ray crystallographic analysis
9. Guo, Z. W. J. Org. Chem. 1993, 58, 5748.
The X-ray crystallographic data were collected at 293 K on