Nitrile biotransformations for the practical synthesis of highly enantiopure azido carboxylic acids and amides, 'click' to functionalized chiral triazoles and chiral β-amino acids

Article abstract of DOI:10.1016/j.tetasy.2006.08.021

Under very mild conditions, biotransformations of racemic azido nitriles using Rhodococcus erythropolis AJ270, a nitrile hydratase/amidase-containing microbial whole-cell catalyst, afforded highly enantiopure, (R)-α-arylmethyl- and (+)-α-cyclohexylmethyl-β-azidopropanoic acids and their (S)- and (-)-carboxamide derivatives in excellent yields. The resulting functionalized chiral organoazides were converted in a straightforward fashion to a pair of antipodes of α-benzyl-β-amino acids (R)-13 and (S)-13. Azido carboxamide (S)-11a and azido carboxylic acid (R)-12a underwent 'click' reactions with diethyl acetylenedicarboxylate and phenylacetylene to produce functionalized chiral triazoles 14 and 15, respectively. The easy preparation of the starting nitrile substrates, highly efficient and enantioselective biotransformation reactions, and versatile utility of the resulting functionalized azido carboxylic acids and amide derivatives, render this method very attractive and practical in organic synthesis.

Full text of DOI:10.1016/j.tetasy.2006.08.021

Tetrahedron: Asymmetry 17 (2006) 2366–2376
Nitrile biotransformations for the practical synthesis of highly
enantiopure azido carboxylic acids and amides, ‘click’
to functionalized chiral triazoles and chiral b-amino acids
Da-You Ma, De-Xian Wang, Qi-Yu Zheng and Mei-Xiang Wang*
Laboratory for Chemical Biology, Center for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences,
Beijing 100080, China
Received 7 August 2006; accepted 30 August 2006
Available online 26 September 2006
Abstract—Under very mild conditions, biotransformations of racemic azido nitriles using Rhodococcus erythropolis AJ270, a nitrile
hydratase/amidase-containing microbial whole-cell catalyst, afforded highly enantiopure, (R)-a-arylmethyl- and (+)-a-cyclohexyl-
methyl-b-azidopropanoic acids and their (S)- and (ꢀ)-carboxamide derivatives in excellent yields. The resulting functionalized chiral
organoazides were converted in a straightforward fashion to a pair of antipodes of a-benzyl-b-amino acids (R)-13 and (S)-13. Azido car-
boxamide (S)-11a and azido carboxylic acid (R)-12a underwent ‘click’ reactions with diethyl acetylenedicarboxylate and phenylacetylene
to produce functionalized chiral triazoles 14 and 15, respectively. The easy preparation of the starting nitrile substrates, highly efficient
and enantioselective biotransformation reactions, and versatile utility of the resulting functionalized azido carboxylic acids and amide
derivatives, render this method very attractive and practical in organic synthesis.
ꢀ 2006 Elsevier Ltd. All rights reserved.
1. Introduction
increasing demand for ‘click’ chemistry in the study of life
science2 and materials science,3 exploration of efficient, and
practical synthesis of highly enantiopure chiral organoaz-
ide entities, particularly functionalized and transformable
ones, is of great importance.
There has been an increasing interest in organoazide com-
pounds since the advent of highly efficient, regiospecific,
and catalytic cycloaddition reactions of azides with termi-
nal acetylenes.1 In addition to their wide applications in
‘click’ synthesis,1–3 organoazides have been known for a
long time as useful and versatile intermediates in organic
synthesis.4 For example, organoazides are powerful 1,3-di-
pole components, which are able to react with a variety of
activated alkenes and alkynes, and other 1,3-dipolarophiles
to form five-membered heterocycles.5 They also act as
the masked amines,4e,6 the source of nitrenes4e,7 and
aza ylides,4e,8 in addition to the well-known Curtius
rearrangement and related reactions. Despite the availabil-
ity of preparative methods for organic azides,4 chiral
organoazides are mainly obtained from diastereoselective
reactions of an azide ion with chiral substrates.4e The syn-
thesis of enantiopure organoazides through catalytic enan-
tioselective reactions is largely unexplored and still remains
as a challenge for synthetic chemists.9 To meet the ever
Biotransformations of nitriles, either through direct con-
version from a nitrile to a carboxylic acid catalyzed by a
nitrilase,10 or through the nitrile hydratase-catalyzed
hydration of a nitrile followed by amide hydrolysis cata-
lyzed by the amidase,11 are effective and environmentally
friendly methods for the production of carboxylic acids
and their amide derivatives.12 Recent studies have shown
that biotransformations of nitriles complement the existing
asymmetric chemical and enzymatic methods for the syn-
thesis of chiral carboxylic acids and their derivatives.13,14
The distinct features of enzymatic transformations of nitr-
iles are the formation of enantiopure carboxylic acids, and
the straightforward generation of enantiopure amides,
which are valuable organonitrogen compounds in synthetic
chemistry. Recently, we13c have shown that Rhodococcus
erythropolis AJ270,15 a nitrile hydratase/amidase-contain-
ing whole-cell catalyst, is able to efficiently and enantio-
selectively transform functionalized nitriles, including
aminonitriles,16 allyl-substituted arylacetonitriles,17 cyclo-
*
Corresponding author. Tel.: +86 10 62565610; fax: +86 10 62564723;
e-mail: mxwang@iccas.ac.cn
0957-4166/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2006.08.021

D.-Y. Ma et al. / Tetrahedron: Asymmetry 17 (2006) 2366–2376
2367
propanecarbonitriles,18 and oxiranecarbonitriles,19 into the
corresponding chiral carboxylic acids and amides. The
intention of further exploring the synthetic applications
of the powerful R. erythropolis AJ270 whole-cell catalyst
in organic chemistry led us to the current study. Consider-
ing the electronic and steric effects of the azido group and
its compatibility with living systems,2 we envisaged that the
biotransformations of azido nitriles might offer us a novel
approach to optically active azido acid and amide deriva-
tives. It is also interesting to look at the influence of azido
group on the reaction efficiency and enantioselectivity of
the nitrile hydratase and the amidase. Herein, we report
an efficient biocatalytic hydrolysis of nitriles for the practi-
cal preparation of highly enantiomerically pure a-aryl-
methyl-b-azido propanoic acids and amide derivatives.
The synthetic utility of the resulting chiral azides will also
be demonstrated in the click synthesis of triazole-contain-
ing chiral carboxylic acids and amides, and in the synthesis
of usual a-branched b-amino acids.
was observed. It was also found that a-azidophenylaceta-
mide 2 was unstable under the incubation conditions,
undergoing slow decomposition to form 2-oxophenylaceta-
mide (Table 1, entry 2). We then tried azido nitrile sub-
strates 4, 7, and 10a in which methylene(s) were
introduced inbetween the stereogenic center and benzene
ring (7 and 10a) or inbetween the stereogenic center and
azido group (4 and 10a). All these substrates and their cor-
responding amides and acids turned out to be stable under
the reaction conditions. Catalyzed by R. erythropolis AJ270
whole cells, both nitriles 4 and 7 were readily hydrated.
However, the sequential biocatalytic hydrolyses of amides
5 and 8 differed remarkably. While 50% conversion of
amide 5 into acid 6 was achieved within several hours,
some took a week to transform half of the amide 8 into
acid 9 (Table 1, entries 3–6). Unfortunately, in all cases,
the enantioselectivity for both nitrile hydration and amide
hydrolysis reactions was unsatisfactory and, therefore, the
method was not a practical way to prepare azido acids 6
and 9 and amides 5 and 8 with high enantiomeric purity.
2. Results and discussion
In sharp contrast to substrates 4 and 7, a-benzyl-b-azido-
propionitrile 10a appeared as an excellent substrate to-
wards the R. erythropolis AJ270 whole-cell catalyst. Thus,
biotransformations of racemic nitrile 10a proceeded effi-
ciently in a short period of time to furnish almost quantita-
tive yields of (S)-azido amide 11a and (R)-azido acid 12a
with excellent enantiomeric excesses (Table 1, entry 8). It
should be noted that the overall high enantioselectivity of
the nitrile biotransformations originates from the com-
bined effect of enantioselective amidase and nitrile hydra-
tase, with the former playing a dominant role, since the
enantiomeric excess of the recovered nitrile (S)-10a is low
(Table 1, entry 7).
No biotransformations of nitriles bearing an azido substi-
tuent have been reported in the literature until now. Inter-
estingly, however, Meldal et al. have observed that, in the
presence of Pseudomonas putida L-aminopeptidase-contain-
ing E. coli cells, a-azidophenylacetamide underwent dy-
namic kinetic resolution to yield optically active (S)-a-
azidophenylacetic acid.20 To start our investigation, we
first examined the R. erythropolis AJ270 whole-cell cata-
lyzed hydrolysis of a-azidophenylacetonitrile 1. Under con-
ventional conditions for the nitrile biotransformation
reaction,16 azido nitrile 1 underwent a highly efficient
hydration reaction to afford optically active amide (ꢀ)-2
and (+)-1 in good yield, albeit with low enantioselectivity
(Table 1, entry 1). Biohydrolysis of a-azidophenylacet-
amide with the amidase in R. erythropolis AJ270 was inef-
fective, and no corresponding a-azidophenylacetic acid 3
To examine the scope of the reaction and influence of the
substituent on the efficiency and enantioselectivity of bio-
transformations, a number of racemic a-arylmethyl-b-azi-
dopropionitriles 10b–h were prepared and subjected to
Table 1. Biotransformations of racemic azido nitriles
EWG
EWG
CN
EWG
N3
N3
N3
N3
( )-10a
( )-7 (EWG = CN)
(-)-8 (EWG = CONH2)
(+)-9 (EWG = CO2H)
( )-1 (EWG = CN)
( )-4 (EWG = CONH2)
(-)-2 (EWG = CONH2)
5
(-)- (EWG = CONH2)
3
(EWG = CO2H)
(-)-6 (EWG = CO2H)
Entry
Nitrile (mmol)
Reaction timea
Nitrile recovered yieldb (%), eec (%)
Amide yieldb (%), eec (%)
Acid yieldb (%), eec (%)
—
1
2
3
4
5
6
7
8
1 (2.0)
1 (0.5)
4 (2.0)
4 (0.5)
7 (2.0)
7 (0.5)
10a (2.0)
10a (2.0)
10 min
3 d
1.5 h
6 h
15 min
7 d
10 min
3.5 h
(+)-1 (51), (29.4)
—
(ꢀ)-2 (45), (64.5)
(ꢀ)-2 (38), (5.1)
d
—
(ꢀ)-4 (47), (15.8)
(ꢀ)-5 (44), (21.8)
(ꢀ)-5 (54), (36.6)
(+)-8 (58), (56.4)
(ꢀ)-8 (41), (48.4)
(R)-11a (36), (11.8)
(S)-11a (48), (>99.5)
—
(ꢀ)-6 (45), (45.0)
(+)-7 (40), (70.8)
—
(S)-10a (54), (15.8)
—
—
(+)-9 (37), (80.0)
—
(R)-12a (49), (96.2)
a Biotransformation was carried out in a suspension of Rhodococcus erythropolis AJ270 cells (2 g wet weight) in phosphate buffer (50 ml, pH 7.0) at 30 ꢁC.
b Isolated yield.
c Determined by HPLC analysis using a chiral column (SI).
d 2-Oxophenylacetamide (19%) was isolated.

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D.-Y. Ma et al. / Tetrahedron: Asymmetry 17 (2006) 2366–2376
CN
N3
CONH2
N3
CO2H
N3
Rhodococcus erythropolis AJ270
R
R
R
+
phosphate buffer, pH 7.0, 30oC
(S)-11a-k
( )-10a-k
(R)-12a-k
Scheme 1. Enantioselective biotransformations of racemic a-substituted b-azidopropionitriles.
incubation with R. erythropolis AJ270 (Scheme 1). As illus-
trated in Table 2, except for nitriles bearing a p-bromophe-
nyl 10h (Table 2, entry 9), a m-chlorophenyl 10f (Table 2,
entry 6) or an o-chlorophenyl substituent 10g (Table 2, en-
try 8), all substrates underwent complete hydration and ca.
50% amide hydrolysis within 5 h. By halving the concentra-
tion of the substrates 10f and 10h, rapid biotransforma-
tions were all effected (Table 2, entries 7 and 10).
Although the nature of the substituent and its substitution
pattern on the benzene ring of the substrates 10a–h played
a part in determining the overall conversion rate, they did
not seem to influence the enantioselectivity of the biotrans-
formations. In all cases of the a-arylmethyl-b-azidopropio-
nitriles 10b–h, biotransformations yielded highly
enantiopure (R)-acid and (S)-amide products.
The aforementioned outcome, along with our previous
studies,13c showed that the nitrile hydratase involved in
R. erythropolis AJ270 is generally less enantioselective
against most of the racemic nitriles, whereas the amidase
exhibits good to excellent enantioselectivity. In most cases,
the nitrile hydratase was not sensitive to the structural vari-
ations of the nitrile substrates, that is, the nitrile hydratase
catalyzes efficient hydration of many nitriles with low to
moderate enantioselectivity. This observation is in agree-
ment with the structure of the nitrile hydratase enzyme,
which contains a spacious active site.21 The action of the
amidase, on the other hand, is highly dependent upon the
structure, particularly the steric features of the amide sub-
strates used. This has been shown clearly by the fact that
the biotransformations of a-azido-b-phenylpropionitrile
4, a-benzyl-b-azidopropionitrile 10a, and a-cyclopropyl-
methyl-b-azidopropionitrile 10j resulted in large differences
in enantiocontrol (Table 1, entry 4; Table 2, entries 1 and
12). This suggests that the presence of both an aryl unit
or a six-membered cyclohexyl moiety and a methylene seg-
ment between the azido group and the stereogenic center in
the structure is crucial for obtaining excellent enantioselec-
tivity. It is worth noting that the azido group must also
have played a very intriguing role in biocatalytic reactions,
as racemic a-benzylpentanenitrile underwent sluggish bio-
transformations (4 days) to afford nearly quantitative
yields of the corresponding amide and acid products but
with 66.5% and 52.8% enantiomeric excess values, respec-
tively. To rationalize the beneficial azido effect is difficult
at this stage because of lack of structural information of
Encouraged by these results, we next studied the biotrans-
formations of racemic b-azidopropionitriles 10i–k that con-
tain an a-alkyl group. Although the conversion of the
alkyl-substituted nitriles 10i–k was almost comparable to
that of aryl-substituted substrates, the replacement of an
aryl group by an alkyl moiety gave rise to a dramatic
change in the enantiocontrol. While the reaction of a-
cyclohexylmethyl-b-azidopropionitrile 10i afforded equally
excellent enantiomeric yields of the products as that of bio-
transformations of a-phenylmethyl-b-azidopropionitrile
10a, only moderate enantioselectivities could be obtained
for the biotransformations of a-cyclopropylmethyl- and
a-propyl-b-azidopropionitriles 10j and 10k (Table 2, en-
tries 11–13).
Table 2. Enantioselective biotransformations of racemic a-substituted b-azidopropionitriles
Entry
10
R
Reaction conditionsa
11 Yieldb (%)
11 eec (%)
12 Yieldb (%)
12 eec (%)
1
2
3
4
5
6
7
8
10a
10b
10c
10d
10e
10f
10f
10g
10h
10h
10i
C6H5
2 mmol, 3.5 h
2 mmol, 1 h
2 mmol, 4.5 h
2 mmol, 4 h
2 mmol, 3.5 h
2 mmol, 24 h
1 mmol, 6 h
2 mmol, 20.5 h
2 mmol, 4.5 hd
1 mmol, 2 h
48
47
48
48
48.5
54
50
48.5
41.5
47
>99.5
>99.5
97.2
>99.5
86.7
81.2
>99.5
97.3
49
48
49
47
44
40
47
48
40
46.5
49
58
48
51
96.2
94.0
>99.5
>99.5
93.2
>99.5
94.8
>99.5
95.3
4-MeO–C6H5
4-Me–C6H5
4-F–C6H5
4-Cl–C6H5
3-Cl–C6H5
3-Cl–C6H5
2-Cl–C6H5
4-Br–C6H5
4-Br–C6H5
C6H11
9
93.5
10
11
12
13
14
>99.5
>99.5
83.0
84.6
>99.5
93.6
2 mmol, 7 h
49
41
48
48
95.5e
58.6e
73.5e
97.4
10j
C3H5
C2H5
C6H5
2 mmol, 1.75 h
2 mmol, 1.5 h
12 mmol, 5 hf
10k
10a
a The biotransformation was carried out in a suspension of Rhodococcus erythropolis AJ270 cells (2 g wet weight) in a phosphate buffer (50 ml, pH 7.0) at
30 ꢁC.
b Isolated yield.
c Determined by HPLC analysis using a chiral column (see SI).
d Nitrile 10h (ꢁ20%) was recovered.
e Enantiomeric excess was determined on its corresponding benzyl ester using HPLC analysis with a chiral column (see SI).
f A suspension of Rhodococcus erythropolis AJ270 cells (12 g wet weight) in 300 ml of phosphate buffer was used.

D.-Y. Ma et al. / Tetrahedron: Asymmetry 17 (2006) 2366–2376
2369
H2, Pd/C, MeOH
CO2H
r.t., 3h
(R)-(-)-12a
93%
NH2
R)-(+)-13
(
H2, Pd/C, MeOH
r.t., 3 h
aq. HCl (6M)
55oC, 43h
CO2H
N3
CO2H
NH2
(S)-(-)-11a
92%
96%
(S)-(-)-13
(S
)-(+)-12a
Scheme 2. Preparation of enantiomerically pure a-benzyl-b-aminopropanoic acid (R)-(+)-13 and its antipode (S)-(ꢀ)-13.
CO2C2H5
CO2C2H5
CONH2
EtOH, reflux, 12h
90%
N
N
N
(S)-(-)-11a +
Ph
CO2C2H5
C2H5O2C
14
CuSO4,
sodium ascorbate,
t-BuOH/H2O
r.t., 2h
CO2H
Ph
N
N
(R)-(-)-12a +
N
Ph
100%
Ph
H
15
Scheme 3. Click reactions of chiral azido amide and azido acid.
the amidase. This might be most probably due to the un-
ique structure and affinity of the azido moiety that facili-
tates its binding and recognition to the active site of the
enzyme.
amino acids as proposed by Seebach,24 has mainly relied on
diastereoselective syntheses utilizing various chiral auxilia-
ries.23 This has been demonstrated by Seebach24 and Jua-
risti.22,25 Biotransformations of azido nitriles, coupled
with chemical hydrolysis, provide a practical, straightfor-
ward and environmentally benign approach to the synthe-
sis of highly enantiomerically pure a-branched b-amino
acids in both antipodal forms.
To show the practical usefulness of this microbial catalytic
process, a multigram scale biotransformation of azido ni-
trile 10a (12 mmol) was carried out in a suspension of R.
erythropolis AJ270 (12 g wet weight) in 300 ml of phos-
phate buffer. After 5 h of incubation, highly enantiomeri-
cally pure (S)-(ꢀ)-amide 11a and (R)-(ꢀ)-acid 12a were
both obtained in more than a gram quantity (Table 2, entry
14). To demonstrate the synthetic applications of chiral azi-
do products, and also in order to examine the stereochem-
istry of biotransformations, both amide 11a and acid 12a
were transformed into b-amino acids. Thus, the catalytic
hydrogenation of acid 12a under very mild conditions
afforded (R)-(+)-a-benzyl-b-aminopropanoic acid (R)-(+)-
13 in 93%, while its antipode (S)-(ꢀ)-13 was readily pro-
duced from chemical hydrolysis of (S)-(ꢀ)-amide 11a,
which gave azido acid (S)-(+)-12a, followed by catalytic
hydrogenation (Scheme 2). No racemarization was ob-
served during the chemical hydrolysis and hydrogenation
processes. The absolute configurations of the b-amino
acids (R)-(+)-13 and (S)-(ꢀ)-13, that were assigned, based
on the comparison of the sign of the specific rotation with
that of authentic samples,22 indicate that the biotransfor-
mation products, azido amide (ꢀ)-11a and azido acid
(ꢀ)-12a are (S)- and (R)-configured, respectively. The ami-
dase involved in R. erythropolis AJ270, therefore, is (R)-
enantioselective against substrates 12a. Chiral b-amino
acids are very important building blocks in the synthesis
of b-lactam antibiotics and b-peptide mimics.23 The synthe-
sis of highly enantiopure a-branched b-amino acids, or b2-
The synthetic potential of enantiopure azido acids and
their amide derivatives resulting from biotransformations
of nitriles has been further demonstrated by the prepara-
tion of functionalized chiral triazole compounds. Scheme
3 shows the convenient and high yielding formation of 14
from a 1,3-cycloaddition reaction of (S)-(ꢀ)-11a with
diethyl acetylenedicarboxylate in refluxing ethanol. Fol-
lowing the Sharpless method,1b azido acid (R)-(ꢀ)-12a
was efficiently clicked to phenylacetylene to afford tri-
azole-containing chiral carboxylic acid 15 in quantitative
yield.
3. Conclusion
In conclusion, we have shown that R. erythropolis AJ270
whole cells can catalyze the hydrolysis of a number of azido
nitriles under very mild conditions. Both the efficiency and
enantioselectivity of biocatalysis, however, were strongly
dependent upon the structures of both nitrile and amide
substrates. While almost all the azido nitriles were effi-
ciently hydrated with the aid of low enantioselective nitrile
hydratase, the amidase exhibited excellent enantioselectiv-
ity against (R)-a-arylmethyl- and (+)-a-cyclohexylmethyl-
b-azidopropanamides. The biocatalytic reaction of racemic

2370
D.-Y. Ma et al. / Tetrahedron: Asymmetry 17 (2006) 2366–2376
azido nitriles has provided a highly efficient and practical
synthesis of highly enantiopure (R)-a-arylmethyl- or (+)-
a-cyclohexylmethyl-b-azidopropanoic acids, and their cor-
responding (S)- or (ꢀ)-amide derivatives. The resulting
functionalized chiral organoazides, which are difficult to
prepare using other methods, can serve as useful intermedi-
ates in the synthesis of polyfunctionalized chiral molecules.
This has been exemplified by the straightforward synthesis
of a pair of antipodes of a-benzyl-b-amino acids through
facile hydrogenation and chemical hydrolysis. Azido car-
boxamide (S)-11a and azido carboxylic acid (R)-12a have
been further demonstrated as reactive species, which read-
ily undergo click chemistry with diethyl acetylenedicarb-
oxylate and phenylacetylene to produce functionalized
chiral triazoles 14 and 15, respectively. The easy prepara-
tion of the starting nitrile substrates, highly efficient and
enantioselective biotransformation reactions, and the ver-
satile utility of the resulting azido carboxylic acids and
amide derivatives render this method very attractive and
practical in organic synthesis. The extension of biotransfor-
mations for the synthesis of various chiral azides and their
applications in organic synthesis are actively being investi-
gated in this laboratory.
room temperature for 5 h. Water (150 ml) was added and
the resulting mixture was extracted with diethyl ether
(3 · 50 ml). After removal of the solvent, the oil residue
was stirred with water (25 ml) at 50 ꢁC to give a-azido-b-
phenylpropanamide 5 as a precipitate (1.925 g, 84%). Fol-
lowing the same procedure for the preparation of 1, 5
was converted into a-azido-b-phenylpropionitrile 4 in
1
71.0% yield: oil; H NMR (300 MHz, CDCl3) d 7.45–7.24
(5H, m), 4.34 (1H, t, J = 7.1 Hz), 3.10 (1H, d,
J = 7.1 Hz); 13C NMR (75 MHz, CDCl3) d 133.5, 129.4,
129.0, 128.2, 115.8, 52.5, 39.1 ppm; IR (KBr) m 2110 (N3)
cmꢀ1; MS (EI) m/z (%) 172 (1) [M]+, 144 (2), 130 (2),
117 (31), 91 (100). Anal. Calcd for C9H8N4: C, 62.78; H,
4.68; N, 32.54. Found: C, 62.66; H, 4.61; N, 32.79.
4.1.3. Preparation of 4-azido-2-phenylbutyronitrile 7. Under
a nitrogen atmosphere, 4-hydroxy-2-phenyl-butyronitrile4
(1.61 g, 10 mmol) was dissolved in dry THF (100 ml), and
triphenyl phosphine (2.88 g, 11 mmol) and hydrazoic acid
solution in toluene (1.6 N, 15 ml) were added while stirring
at room temperature. Diisopropyl azodicarboxylate
(11 mmol) was added dropwise and then the mixture was
kept for stirring for 30 min. Water (50 ml) was added into
the reaction mixture, and THF removed under vacuum.
After extraction with diethyl ether (3 · 50 ml), the combined
organic layer was concentrated to 20 ml after which petro-
leum ether (20 ml) was added to precipitate triphenyl pho-
spine oxide. The solvent was removed and the residue
subjected to chromatography using a silica gel column eluted
with a mixture of petroleum ether and ethyl acetate (10:1). 4-
Azido-2-phenylbutyronitrile 7 (1.656 g, 89%) was obtained
4. Experimental
4.1. Preparation of starting nitriles and their spectroscopic
data
4.1.1. Preparation of racemic a-azidophenylacetonitrile 1.
To a mixture of racemic a-azidophenylacetic acid1 (4.425 g,
25 mmol) in dry THF (70 ml) at ꢀ25 ꢁC was added trieth-
ylamine (3.5 ml, 25 mmol) under a nitrogen atmosphere.
After stirring for 5 min, ethyl chlorocarbonate (2.4 ml)
was added and the resulting mixture was stirred for another
15 min. Dry ammonia gas was then bubbled through the
mixture for 45 min. The cooling bath was removed and
the mixture was stirred at ambient temperature to allow
the temperature of the mixture to increase to 0 ꢁC. The
reaction mixture was mixed with water (100 ml) and ex-
tracted with diethyl ether (3 · 70 ml). After drying over
anhydrous MgSO4 and removal of the solvent, the residue
was crystallized in a mixture of dichloromethane and
petroleum ether at ꢀ75 ꢁC to give a-azidophenylaceto-
amide 2 (1.82 g, 39%). To a solution of 2 (500 mg,
2.84 mmol) in dry DMF (60 ml) at 0 ꢁC was added SOCl2
(0.31 ml). After stirring for 25 min, ice water (60 ml) was
added and the mixture was extracted with diethyl ether
(3 · 30 ml). The organic layer was dried over with anhy-
drous MgSO4 and the solvent removed under vacuum. Col-
umn chromatography using silica gel eluted with a mixture
of petroleum ether and ethyl acetate (30:1) gave a-azido-
phenylacetonitrile 12 (365 mg, 81%) as a colorless liquid:
1H NMR (300 MHz, CDCl3) d 7.49 (5H, s), 5.23 (1H, s);
13C NMR (75 MHz, CDCl3) d 131.0, 130.5, 129.6, 127.4,
115.5, 54.4 ppm; IR (KBr) m 2111 cmꢀ1 (–N3).
1
as a colorless oil: H NMR (300 MHz, CDCl3) d 7.41–7.33
(5H, m), 3.97 (1H, dd, J = 6.9, 8.4 Hz), 3.57–3.48 (1H, m),
3.44–3.36 (1H, m), 2.21–2.07 (2H, m); 13C NMR (75 MHz,
CDCl3) d 134.5, 129.4, 128.5, 127.4, 120.0, 48.2, 34.9,
34.3 ppm; IR (KBr) m 2242 (CN), 2102 (N3) cmꢀ1; MS
(EI) m/z (%) 158 (22) [M–28]+, 157 (43), 156 (59), 155
(100), 130 (47), 129 (84), 104 (72), 103 (56), 102 (30). Anal.
Calcd for C10H10N4: C, 64.50; H, 5.41; N, 30.09. Found:
C, 64.90; H, 5.35; N, 30.12.
4.1.4. Preparation of b-azido-a-benzylpropionitrile 10a. To
a suspension of methyl 2-cyano-3-phenyl acrylate5 (11.2 g,
60 mmol) in isopropanol (180 ml) cooled in a water bath
was added sodium borohydride (6.84 g) with the resulting
mixture stirred overnight at ambient temperature. Acetic
acid (30%) was carefully added to the reaction mixture to
quench the remaining sodium borohydride until no bub-
bling was observed. 2-Propanol was then removed under
vacuum and the residue basified to pH 10 with aqueous so-
dium hydroxide (1 M) and extracted with diethyl ether
(3 · 50 ml). After drying over with anhydrous MgSO4
and removal of solvent, a-benzyl-b-hydroxypropionitrile
1
(9.44 g, 98%) was isolated as a colorless liquid: H NMR
(300 MHz, CDCl3) d 7.35–7.24 (5H, m), 3.77 (2H, s),
2.97 (3H, s), 2.29 (1H, br); 13C NMR (75 MHz, CDCl3) d
136.4, 129.0, 128.9, 127.4, 120.5, 61.8, 36.8, 34.5 ppm; IR
(KBr) m 3450 (OH), 2245 cmꢀ1 (C@O). Under a nitrogen
atmosphere, a-benzyl-b-hydroxypropionitrile (805 mg,
5 mmol) was dissolved in dry THF (50 ml), and triphenyl
phosphine (1.57 g, 6 mmol) and hydrazoic acid solution
in toluene (1.6 M, 3 ml) were added. After cooling down
4.1.2. Preparation of a-azido-b-phenylpropionitrile 4. a-
Bromo-b-phenylpropanamide3 (1.824 g) was dissolved in
DMSO (12 ml) and a solution of sodium azide in DMSO
(17.6 ml, 0.5 M) was added. The mixture was stirred at

D.-Y. Ma et al. / Tetrahedron: Asymmetry 17 (2006) 2366–2376
2371
to 5 ꢁC, diisopropyl azodicarboxylate (6 mmol) was added
dropwise within 45 s and then stirred for another 30 s.
Water (50 ml) was then added to the reaction mixture,
and THF was removed under vacuum. The mixture was ex-
tracted with diethyl ether (3 · 40 ml) and the combined
diethyl ether solution was concentrated to 10 ml. The addi-
tion of petroleum ether (10 ml) resulted in the precipitation
of triphenyl phospine oxide. After removal of solvent and a
silica gel column chromatography eluting with a mixture of
petroleum ether and ethyl acetate (10:1), b-azido-a-benzyl-
propionitrile 10a (441 mg, 47%) was obtained as a colorless
oil: 1H NMR (300 MHz, CDCl3) d 7.36–7.23 (5H, m),
3.54–3.47 (2H, m), 3.03–2.94 (3H, m); 13C NMR
(75 MHz, CDCl3) d 135.5, 129.1, 129.0, 127.7, 119.4,
50.9, 35.4, 33.9 ppm; IR (KBr) m 2244 (CN), 2108 (N3)
cmꢀ1; MS (EI) m/z (%) 158 (100) [Mꢀ28]+, 157 (62), 140
(21), 130 (63), 105 (19), 91 (43). Anal. Calcd for
C10H10N4: C, 64.50; H, 5.41; N, 30.09. Found: C, 64.55;
H, 5.26; N, 30.40.
(34), 141 (12), 139 (31), 127 (31), 125 (100). Anal. Calcd
for C10H9N4Cl: C, 54.43; H, 4.11; N, 25.39. Found: C,
54.50; H, 4.09; N, 25.29.
4.1.5.5. b-Azido-a-(m-chlorophenylmethyl)propionitrile
1
10f. Oil; H NMR (300 MHz, CDCl3) d 7.33–7.16 (4H,
m), 3.55 (2H, d, J = 5.7 Hz), 3.04–2.95 (3H, m); 13C
NMR (75 MHz, CDCl3) d 137.4, 134.8, 130.5, 129.2,
128.0, 127.3, 119.0, 50.9, 35.0, 33.7 ppm; IR (KBr) m 2248
(CN), 2109 (N3), 1289 cmꢀ1; MS (EI) m/z (%) 194 (15)
[Mꢀ26]+, 193 (17), 192 (52), 191 (41), 163 (28), 157 (73),
141 (19), 139 (68), 128 (55), 127 (31), 125 (100). Anal. Calcd
for C10H9N4Cl: C, 54.43; H, 4.11; N, 25.39. Found: C,
54.54; H, 4.11; N, 25.35.
4.1.5.6.
b-Azido-a-(o-chlorophenylmethyl)propionitrile
1
10g. Oil; H NMR (300 MHz, CDCl3) d 7.44–7.28 (4H,
m), 3.61 (1H, dd, J = 7.5, 12.4 Hz), 3.56 (1H, dd, J = 5.4,
12.4 Hz), 3.22–3.07 (3H, m); 13C NMR (75 MHz, CDCl3)
d 134.0, 133.5, 131.7, 130.0, 129.3, 127.4, 119.1, 51.3,
4.1.5. Nitriles 10b–k were prepared following the same
procedure reported for the preparation of 10a
33.7, 32.2 ppm; IR (KBr) m 2245 (CN), 2108 (N3) cmꢀ1
;
MS (EI) m/z (%) 194 (22) [Mꢀ26]+, 192 (81), 157 (100),
127 (25), 125 (84). Anal. Calcd for C10H9N4Cl: C, 54.43;
H, 4.11; N, 25.39. Found: C, 54.36; H, 4.13; N, 25.61.
4.1.5.1. b-Azido-a-(p-methoxyphenylmethyl)propionitrile
10b. Oil; 1H NMR (300 MHz, CDCl3) d 7.15 (2H, d,
J = 8.7 Hz), 6.88 (2H, d, J = 8.7 Hz), 3.79 (3H, s), 3.48–
3.46 (2H, m), 2.95–2.88 (3H, m); 13C NMR (75 MHz,
CDCl3) d 159.1, 130.2, 127.5, 119.5, 114.4, 55.3, 50.9,
4.1.5.7.
b-Azido-a-(p-bromophenylmethyl)propionitrile
10h. Oil; 1H NMR (300 MHz, CDCl3) d 7.40 (2H, d,
J = 8.4 Hz), 7.05 (2H, d, J = 8.4 Hz), 3.40 (2H, d,
J = 8.2 Hz), 2.92–2.83 (3H, m); 13C NMR (75 MHz,
CDCl3) d 134.5, 132.1, 130.8, 121.7, 119.1, 50.9, 34.7,
33.7 ppm; IR (KBr) m 2245 (CN), 2109 (N3) cmꢀ1; MS
(EI) m/z (%) 238 (97) [Mꢀ28]+, 236 (100), 169 (65), 171
(64), 157 (84), 140 (33). Anal. Calcd for C10H9N4Br: C,
45.30; H, 3.42; N, 21.13. Found: C, 45.11; H, 3.38; N,
21.03.
34.5, 34.1 ppm; IR (KBr) m 2251 (CN), 2107 (N3) cmꢀ1
;
MS (EI) m/z (%) 216 (4) [M]+, 188 (100), 145 (30), 121
(93). Anal. Calcd for C11H12N4O: C, 61.10; H, 5.59; N,
25.91. Found: C, 61.07; H, 5.60; N, 25.79.
4.1.5.2. b-Azido-a-(p-methylphenylmethyl)propionitrile
10c. Oil; 1H NMR (300 MHz, CDCl3) d 7.20 (2H, d,
J = 8.3 Hz), 7.16 (2H, d, J = 8.3 Hz), 3.57–3.48 (2H, m),
3.03–2.93 (3H, m), 2.37 (3H, s); 13C NMR (75 MHz,
CDCl3) d 137.4, 132.4, 130.0, 129.0, 119.5, 50.9, 35.0,
4.1.5.8. b-Azido-a-cyclohexylmethylpropionitrile 10i.
Oil; 1H NMR (300 MHz, CDCl3) d 3.52 (2H, d,
J = 6.3 Hz), 2.90–2.80 (1H, m), 1.76–0.91 (13H, m); 13C
NMR (75 MHz, CDCl3) d 120.0, 52.4, 37.0, 35.2, 33.5,
32.2, 29.9, 26.2, 25.9, 25.8 ppm; IR (KBr) m 2233 (CN),
2105 (N3) cmꢀ1; MS (EI) m/z (%) 164 (12) [Mꢀ28]+,
135(3), 121 (100), 108 (16). Anal. Calcd for C10H16N4: C,
62.47; H, 8.39; N, 29.14. Found: C, 62.25; H, 8.12; N,
29.37.
34.0, 21.1 ppm; IR (KBr) m 2244 (CN), 2107 (N3) cmꢀ1
;
MS (EI) m/z (%) 172 (100) [Mꢀ28]+, 171 (34), 157 (50),
144 (24), 143 (25), 119 (27), 118 (22), 105 (77). Anal. Calcd
for C11H12N4: C, 65.98; H, 6.04; N, 27.98. Found: C, 65.82;
H, 5.97; N, 27.98.
4.1.5.3.
b-Azido-a-(p-fluorophenylmethyl)propionitrile
1
10d. Oil; H NMR (300 MHz, CDCl3) d 7.19–7.13 (2H,
m), 7.00–6.94 (2H, m), 3.42 (2H, d, J = 8.3 Hz), 2.91–
2.83 (3H, m); 13C NMR (75 MHz, CDCl3) d 162.3 (d,
J = 243.7 Hz), 131.2 (d, J = 3.2 Hz), 130.7 (d,
J = 8.1 Hz), 119.1, 115.9 (d, J = 21.4 Hz), 50.9, 34.5,
4.1.5.9. b-Azido-a-cyclopropylmethylpropionitrile 10j.
Oil; 1H NMR (300 MHz, CDCl3) d 3.61 (1H, dd,
J = 12.3, 6.8 Hz), 3.56 (1H, dd, J = 12.3, 6.1 Hz), 2.90–
2.81 (1H, m), 1.70–1.63 (1H, m), 1.57–1.50 (1H, m),
0.93–0.79 (1H, m), 0.68–0.53 (2H, m), 0.28–0.11 (2H, m);
13C NMR (75 MHz, CDCl3) d 119.9, 51.7, 34.5, 32.7, 8.3,
4.9, 4.4 ppm; IR (KBr) m 2244 (CN), 2108 (N3) cmꢀ1; MS
(EI) m/z (%) 122 (38) [Mꢀ28]+, 107(9), 93 (34), 82 (75),
81 (100). Anal. Calcd for C7H10N4: C, 55.98; H, 6.71; N,
37.31. Found: C, 56.16; H, 6.52; N, 37.04.
34.0 ppm; IR (KBr) m 2248 (CN), 2109 (N3), 1509 cmꢀ1
;
MS (EI) m/z (%) 176 (100) [Mꢀ28]+, 175 (48), 161 (15),
158 (27), 149 (24), 148 (52), 109 (32). Anal. Calcd for
C10H9N4F: C, 58.82; H, 4.44; N, 27.44. Found: C, 58.72;
H, 4.52; N, 27.27.
4.1.5.4.
b-Azido-a-(p-chlorophenylmethyl)propionitrile
10e. Oil; 1H NMR (300 MHz, CDCl3) d 7.36 (2H, d,
J = 8.4 Hz), 7.21 (2H, d, J = 8.4 Hz), 3.53 (2H, d,
J = 3.7 Hz), 3.00–2.93 (3H, m); 13C NMR (75 MHz,
CDCl3) d 133.9, 133.7, 130.5, 129.2, 119.0, 50.9, 34.7,
33.8 ppm; IR (KBr) m 2248 (CN), 2108 (N3) cmꢀ1; MS
(EI) m/z (%) 194 (8) [Mꢀ26]+, 192 (25), 165 (15), 163
4.1.5.10. a-Azidomethylpentanenitrile 10k. Oil; 1H
NMR (300 MHz, CDCl3) d 3.55 (1H, dd, J = 12.3,
6.8 Hz), 3.50 (1H, dd, J = 12.3, 6.1 Hz), 2.81–2.72 (1H,
m), 1.73–1.43 (4H, m), 0.98 (3H, t, J = 7.1 Hz); 13C
NMR (75 MHz, CDCl3) d 119.8, 52.0, 32.1, 31.5, 20.1,

2372
D.-Y. Ma et al. / Tetrahedron: Asymmetry 17 (2006) 2366–2376
13.5 ppm; IR (KBr) m 2240 (CN), 2107 (N3) cmꢀ1; MS (EI)
m/z (%) 110 (15) [Mꢀ28]+, 95(34), 81 (46), 54 (100). Anal.
Calcd for C6H10N4: C, 52.16; H, 7.29; N, 40.55. Found: C,
51.98; H, 7.33; N, 40.69.
56.83; H, 5.30; N, 29.46. Found: C, 56.98; H, 5.36; N,
29.72.
25
4.2.3. (ꢀ)-a-Azido-b-phenylpropanoic acid 6. Oil; ½aꢂD
¼
ꢀ25:2 (c 2.300, CHCl3); ee 45.0% (chiral HPLC analysis);
1H NMR (300 MHz, CDCl3) d 10.90 (1H, br) 7.37–7.24
(5H, m), 4.16 (1H, dd, J = 9.0, 5.0 Hz), 3.24 (1H, dd,
J = 14.1, 5.0 Hz), 3.04 (1H, dd, J = 14.1, 9.0 Hz); 13C
NMR (75 MHz, CDCl3) d 176.2, 135.6, 129.2, 128.8,
127.5, 63.1, 37.5 ppm; IR (KBr) m 3445–2600 (COOH),
2116 (N3), 1719 cmꢀ1 (C@O); MS (EI) m/z (%) 191 (2)
[M]+, 163 (3) 148 (1), 119 (50), 118 (33), 92 (41), 91
(100). Anal. Calcd for C9H9N3O2: C, 56.54; H, 4.74; N,
21.98. Found: C, 56.54; H, 4.87; N, 21.63.
4.2. General procedure for the biotransformations of nitriles
To an Erlenmeyer flask (150 ml) with a screw cap was
added R. erythropolis AJ270 cells15 (2 g wet weight) and
potassium phosphate buffer (0.1 M, pH 7.0, 50 ml); the
resting cells were activated at 30 ꢁC for 0.5 h with orbital
shaking. The racemic nitrile was added in one portion to
the flask and the mixture incubated at 30 ꢁC using an orbi-
tal shaker (200 rpm). The reaction, monitored by TLC and
HPLC, was quenched after a specified period of time (see
Tables 1 and 2) by removing the biomass through a Celite
pad filtration. The resulting aqueous solution was basified
to pH 12 with aqueous NaOH (2 M). Extraction with ethyl
acetate (3 · 60 ml) gave, after drying over MgSO4, concen-
tration and a silica gel column chromatography eluting
with a mixture of petroleum ether and acetone (2:1), the
amide product. The aqueous solution was then acidified
using aqueous HCl (2 M) to pH 2 and extracted with ethyl
acetate (3 · 60 ml). The acid product was obtained after
drying over MgSO4, removal of the solvent under vacuum,
followed by a silica gel column chromatography eluted
with a mixture of petroleum ether and acetone (from 20:1
to 2:1). All products were characterized by their spectral
data and comparison of the melting points and specific
rotation with that of the known compounds, which are
listed as follows, or by full characterization. The absolute
configurations of a-arylmethyl-b-azidopropanoic acids
12b–h and amides 11b–h are tentatively assigned as (R)
and (S), respectively, as that of 12a and 11a, based on
the assumption that the introduction of a substituent on
the benzene ring does not cause an inversion of the sign
of the specific rotation. For other chiral products, absolute
configurations were not determined. Enantiomeric excess
values were obtained from HPLC analysis (see SI).
4.2.4. (+)-4-Azido-2-phenylbutanamide 8. Mp 56–60 ꢁC;
25
½aꢂD ¼ þ64:3 (c 2.425, CHCl3); ee 56.4% (chiral HPLC
1
analysis); H NMR (300 MHz, CDCl3) d 7.36–7.27 (5H,
m), 5.74 (1H, br), 5.45 (1H, br), 3.58 (1H, t, J = 7.6 Hz),
3.37–3.29 (1H, m), 3.25–3.16 (1H, m), 2.48–2.37 (1H, m),
2.05–1.93 (1H, m); 13C NMR (75 MHz, CDCl3) d 174.9,
138.7, 129.2, 128.0, 127.8, 49.4, 49.2, 32.1 ppm; IR (KBr)
m 3406, 3184 (CONH2), 2102, 2083 (N3), 1654 cmꢀ1
(C@O); MS (EI) m/z (%) 176 (1) [Mꢀ28]+, 173 (7), 159
(100), 130 (85). Anal. Calcd for C10H12N4O: C, 58.81; H,
5.92; N, 27.43. Found: C, 58.93; H, 5.89; N, 27.44.
4.2.5. (+)-4-Azido-2-phenylbutanoic acid 9. Mp 66–68 ꢁC;
25
½aꢂD ¼ þ64:0 (c 1.000, CHCl3); ee 83.0% (chiral HPLC
1
analysis); H NMR (300 MHz, CDCl3) d 7.37–7.25 (5H,
m), 3.73 (1H, t, J = 7.6 Hz), 3.36–3.28 (1H, m), 3.23–3.14
(1H, m), 2.40–2.28 (1H, m), 2.09–1.97 (1H, m); 13C
NMR (75 MHz, CDCl3) d 179.1, 137.1, 129.0, 128.1,
127.9, 49.0, 48.3, 31.9 ppm; IR (KBr) m 3065–2517
(COOH), 2141, 2089 (N3), 1695 cmꢀ1 (C@O); MS (EI)
m/z (%) 177 (2) [Mꢀ28]+, 161 (60), 159 (71), 132 (58),
130 (100), 118 (48), 117 (95). Anal. Calcd for
C10H11N3O2: C, 58.53; H, 5.40; N, 20.48. Found: C,
58.45; H, 5.39; N, 20.53.
25
4.2.6. (S)-b-Azido-a-benzylpropanamide 11a. Oil; ½aꢂD
¼
4.2.1. (ꢀ)-a-Azidophenylacetoamide 2. Mp 112–114 ꢁC;
ꢀ31:9 (c 2.950, CHCl3); ee >99% (chiral HPLC analysis);
1H NMR (300 MHz, CDCl3) d 7.38–7.18 (5H, m), 5.77
(1H, br), 5.52 (1H, br), 3.61 (1H, dd, J = 12.1, 8.5 Hz),
3.42 (1H, dd, J = 12.1, 4.9 Hz), 2.94 (1H, dd, J = 13.6,
8.5 Hz), 2.80 (1H, dd, J = 13.6, 6.6 Hz), 2.65–2.61 (1H,
m); 13C NMR (75 MHz, CDCl3) d 174.9, 138.1, 128.9,
128.8, 126.9, 52.3, 48.5, 36.2 ppm; IR (KBr) m 3334, 3188
(CONH2), 2103 (N3), 1668 cmꢀ1 (C@O); MS (EI) m/z
(%) 176 (25) [Mꢀ28]+, 159 (66), 158 (30), 146 (17), 132
(34), 131 (50), 130 (100). Anal. Calcd for C10H12N4O: C,
58.81; H, 5.92; N, 27.43. Found: C, 58.44; H, 5.82; N,
27.83.
25
½aꢂD ¼ ꢀ112:2 (c 2.300, CHCl3); ee 64.5% (chiral HPLC
analysis); 1H NMR (300 MHz, CDCl3) d 7.41 (5H, s),
6.44 (1H, br), 6.39 (1H, br), 5.02 (1H, s); 13C NMR
(75 MHz, CDCl3) d 170.9, 134.7, 129.3, 129.2, 127.8,
67.1 ppm; IR (KBr) m 3426, 3162 (CONH2), 2106 (N3),
1662 cmꢀ1 (C@O); MS (EI) m/z (%) 148 (2) [Mꢀ28]+,
132 (9), 120 (5), 104 (100). Anal. Calcd for C8H8N4O: C,
54.54; H, 4.58; N, 31.80. Found: C, 54.47; H, 4.61; N,
31.78.
4.2.2. (ꢀ)-a-Azido-b-phenylpropanamide 5. Mp 79–80 ꢁC;
25
½aꢂD ¼ ꢀ35:8 (c 2.850, CHCl3); ee 36.6% (chiral HPLC
1
analysis); H NMR (300 MHz, CDCl3) d 7.37–7.26 (5H,
4.2.7. (R)-b-Azido-a-benzylpropanoic acid 12a. Oil;
25
m), 6.24 (1H, br), 6.08 (1H, br), 4.19 (1H, dd, J = 8.4,
4.3 Hz), 3.35 (1H, dd, J = 14.1, 4.3 Hz), 3.02 (1H, dd,
J = 14.1, 8.4 Hz); 13C NMR (75 MHz, CDCl3) d 171.5,
136.1, 129.5, 128.7, 127.3, 65.3, 38.6 ppm; IR (KBr) m
3451, 3184 (CONH2), 2131, 2102 (N3), 1672 cmꢀ1
(C@O); MS (EI) m/z (%) 162 (30) [Mꢀ28]+, 147 (19), 131
(4), 118 (30), 91 (100). Anal. Calcd for C9H10N4O: C,
½aꢂD ¼ ꢀ29:0 (c 2.000, CHCl3); ee >99% (chiral HPLC
1
analysis); H NMR (300 MHz, CDCl3) d 11.36 (1H, br)
7.35–7.18 (5H, m), 3.49 (2H, d, J = 5.8 Hz), 3.12–3.05
(1H, m), 2.95–2.16 (2H, m); 13C NMR (75 MHz, CDCl3)
d 179.3, 137.4, 129.0, 128.8, 127.0, 50.9, 46.7, 34.9 ppm;
IR (KBr) m 3086–2608 (COOH), 2104 (N3), 1710 cmꢀ1
(C@O); MS (EI) m/z (%) 177 (11) [Mꢀ28]+, 176 (9), 147

D.-Y. Ma et al. / Tetrahedron: Asymmetry 17 (2006) 2366–2376
2373
(19), 133 (48), 132 (100), 130 (36), 117 (32), 115 (28), 91
(36). Anal. Calcd for C10H11N3O2: C, 58.53; H, 5.40; N,
20.48. Found: C, 58.25; H, 5.39; N, 20.71.
CDCl3) d 7.19–7.15 (2H, m), 7.04–6.98 (2H, m), 5.88
(1H, br), 5.65 (1H, br), 3.61 (1H, dd, J = 12.2, 8.4 Hz),
3.44 (1H, dd, J = 12.2, 5.0 Hz), 2.93 (1H, dd, J = 13.7,
8.6 Hz), 2.79 (1H, dd, J = 13.7, 6.4 Hz), 2.63–2.60 (1H,
m); 13C NMR (75 MHz, CDCl3) d 174.8, 161.8 (d,
J = 243.7 Hz), 133.7 (d, J = 3.2 Hz), 130.3 (d, J =
7.9 Hz), 115.6 (d, J = 21.2 Hz), 52.3, 48.6, 35.3 ppm; IR
(KBr) m 3338, 3194 (CONH2), 2104 (N3), 1668 (C@O)
cmꢀ1; MS (EI) m/z (%) 194 (8) [Mꢀ28]+, 178 (64), 161
(42), 148 (54), 133 (50), 109 (100). Anal. Calcd for
C10H11N4OF: C, 54.04; H, 4.99; N, 25.21. Found: C,
54.01; H, 4.93; N, 25.33.
4.2.8. (S)-b-Azido-a-(p-methoxyphenylmethyl)propanamide
25
11b. Mp 73–74 ꢁC; ½aꢂD ¼ ꢀ29:9 (c 1.625, CHCl3); ee
>99% (chiral HPLC analysis); 1H NMR (300 MHz,
CDCl3)
d 7.11 (2H, d, J = 8.7 Hz), 6.85 (2H, d,
J = 8.7 Hz), 6.00 (1H, br), 5.72 (1H, br), 3.79 (3H, s),
3.59 (1H, dd, J = 12.2, 8.5 Hz), 3.40 (1H, dd, J = 12.2,
4.9 Hz), 2.89 (1H, dd, J = 13.7, 8.4 Hz), 2.75 (1H, dd,
J = 13.7, 6.6 Hz), 2.63–2.60 (1H, m); 13C NMR (75 MHz,
CDCl3) d 175.2, 158.4, 130.1, 129.9, 114.1, 55.2, 52.3,
48.5, 35.3 ppm; IR (KBr) m 3337, 3194 (CONH2), 2103
(N3), 1668 (C@O) cmꢀ1; MS (ESI+) m/z 256.7 [M+Na]+.
Anal. Calcd for C11H14N4O2: C, 56.40; H, 6.02; N, 23.92.
Found: C, 56.38; H, 6.01; N, 24.09.
4.2.13. (R)-b-Azido-a-(p-fluorophenylmethyl)propanoic acid
25
12d. Oil; ½aꢂD ¼ ꢀ27:3 (c 2.125, CHCl3); ee >99% (chiral
HPLC analysis); 1H NMR (300 MHz, CDCl3) d 10.75 (1H,
br) 7.20–7.16 (2H, m), 7.06–7.00 (2H, m), 3.52 (2H, d,
J = 5.6 Hz), 3.09–3.03 (1H, m), 2.93–2.87 (2H, m); 13C
NMR (75 MHz, CDCl3) d 179.1, 161.9 (d, J = 243.7 Hz),
133.1 (d, J =3.4 Hz), 130.4 (d, J = 8.0 Hz), 115.6 (d,
J = 21.2 Hz), 50.9, 46.8, 34.0 ppm; IR (KBr) m 3121–2618
(COOH), 2105 (N3), 1713 (C@O), 1511, 1223 cmꢀ1; MS
(EI) m/z (%) 195 (17) [Mꢀ28]+, 180 (16), 166 (14), 151
(77), 150 (100), 133 (34), 109 (77). Anal. Calcd for
C10H10N3O2F: C, 53.81; H, 4.52; N, 18.83 Found: C,
53.56; H, 4.54; N, 19.14.
4.2.9.
(R)-b-Azido-a-(p-methoxyphenylmethyl)propanoic
25
acid 12b. Oil; ½aꢂD ¼ ꢀ38:2 (c 2.010, CHCl3); ee >99%
(chiral HPLC analysis); 1H NMR (300 MHz, CDCl3) d
10.00 (1H, br) 7.14 (2H, d, J = 8.7 Hz), 6.89 (2H, d,
J = 8.7 Hz), 3.83 (3H, s), 3.52–3.50 (2H, m), 3.09–3.04
(1H, m), 2.94–2.81 (2H, m); 13C NMR (75 MHz, CDCl3)
d 179.2, 158.5, 130.0, 129.4, 114.2, 55.3, 51.0, 46.9,
34.1 ppm; IR (KBr) m 3038–2555 (COOH), 2104 (N3),
1710 (C@O) cmꢀ1; MS (ESI+) m/z 257.9 [M+Na]+. Anal.
Calcd for C11H13N3O3: C, 56.16; H, 5.57; N, 17.86. Found:
C, 56.04; H, 5.47; N, 17.86.
4.2.14. (S)-b-Azido-a-(p-chlorophenylmethyl)propanamide
25
11e. Mp 63–65 ꢁC; ½aꢂD ¼ ꢀ29:2 (c 1.370, CHCl3); ee
86.7% (chiral HPLC analysis); 1H NMR (300 MHz,
CDCl3) 7.29 (2H, d, J = 8.4 Hz), 7.14 (2H, d,
J = 8.4 Hz), 5.78 (1H, br), 5.58 (1H, br), 3.61 (1H, dd,
J = 12.2, 8.4 Hz), 3.43 (1H, dd, J = 12.2, 5.1 Hz), 2.93
(1H, dd, J = 13.7, 8.7 Hz), 2.78 (1H, dd, J = 13.7,
6.3 Hz), 2.62–2.52 (1H, m); 13C NMR (75 MHz, CDCl3)
d 174.5, 136.6, 132.7, 130.3, 128.9, 52.3, 48.4, 35.4 ppm;
IR (KBr) m 3328, 3190 (CONH2), 2102 (N3), 1664 cmꢀ1
(C@O); MS (EI) m/z (%) 238 (1) [M]+, 212 (18), 210 (54),
196 (20), 194 (71), 167 (48), 166 (91), 165 (100), 164
(100), 158 (60), 132 (16), 130 (65), 127 (31), 125 (88). Anal.
Calcd for C10H11N4OCl: C, 50.32; H, 4.65; N, 23.47.
Found: C, 50.55; H, 4.68; N, 23.27.
4.2.10. (S)-b-Azido-a-(p-methylphenylmethyl)propanamide
25
11c. Mp 79–80 ꢁC; ½aꢂD ¼ ꢀ34:9 (c 2.980, CHCl3); ee
>99% (chiral HPLC analysis); 1H NMR (300 MHz,
CDCl3)
d 7.05 (2H, d, J = 8.2 Hz), 7.00 (2H, d,
J = 8.2 Hz), 5.55 (1H, br), 5.43 (1H, br), 3.53 (1H, dd,
J = 12.1, 8.4 Hz), 3.35 (1H, dd, J = 12.1, 4.8 Hz), 2.83
(1H, dd, J = 13.6, 8.4 Hz), 2.69 (1H, dd, J = 13.6,
6.5 Hz), 2.56–2.52 (1H, m), 2.25 (3H, s); 13C NMR
(75 MHz, CDCl3) d 174.9, 136.5, 135.0, 129.4, 128.7,
52.3, 48.5, 35.8, 21.0 ppm; IR (KBr) m 3390, 3199
(CONH2), 2100 (N3), 1642 (C@O) cmꢀ1; MS (EI) m/z
(%) 218 (1) [M]+, 190 (51), 173 (84), 160 (36), 146 (64),
145 (84), 144 (100), 130 (51), 105 (49). Anal. Calcd for
C11H14N4O: C, 60.53; H, 6.47; N, 25.67. Found: C,
60.45; H, 6.53; N, 25.57.
4.2.15. (R)-b-Azido-a-(p-chlorophenylmethyl)propanoic acid
25
12e. Oil; ½aꢂD ¼ ꢀ24:6 (c 1.055, CHCl3); ee >99% (chiral
1
HPLC analysis); H NMR (300 MHz, CDCl3) 10.40 (1H,
4.2.11. (R)-b-Azido-a-(p-methylphenylmethyl)propanoic acid
br), 7.31 (2H, d, J = 8.4 Hz), 7.15 (2H, d, J = 8.4 Hz),
3.52 (2H, d, J = 5.6 Hz), 3.12–3.03 (1H, m), 2.94–2.85
(2H, m); 13C NMR (75 MHz, CDCl3) d 179.0, 135.9,
132.9, 130.3, 128.9, 50.9, 46.6, 34.1 ppm; IR (KBr) m
3092–2566 (COOH), 2105 (N3), 1711 (C@O) cmꢀ1; MS
(EI) m/z (%) 239 (1) [M]+, 213 (3), 211 (6), 169 (21), 168
(26), 167 (72), 166 (88), 132 (100), 127 (16), 125 (53). Anal.
Calcd for C10H10N3O2Cl: C, 50.12; H, 4.21; N, 17.53.
Found: C, 50.04; H, 4.16; N, 17.77.
25
12c. Oil; ½aꢂD ¼ ꢀ34:0 (c 2.705, CHCl3); ee >99% (chiral
HPLC analysis); 1H NMR (300 MHz, CDCl3) d 10.44 (1H,
br) 7.16 (2H, d, J = 8.1 Hz), 7.11 (2H, d, J = 8.1 Hz), 3.51
(2H, d, J = 5.0 Hz), 3.12–3.06 (1H, m), 2.96–2.82 (2H, m),
2.36 (3H, s); 13C NMR (75 MHz, CDCl3) d 179.2, 136.5,
134.3, 129.4, 128.8, 51.0, 46.8, 34.6, 21.0 ppm; IR (KBr) m
3024–2562 (COOH), 2103 (N3), 1709 (C@O) cmꢀ1; MS
(EI) m/z (%) 191 (29) [Mꢀ28]+, 176 (27), 147 (78), 146
(100), 132 (84), 105 (44). Anal. Calcd for C11H13N3O2: C,
60.26; H, 5.98; N, 19.17. Found: C, 60.38; H, 6.03; N,
19.39.
4.2.16. (S)-b-Azido-a-(m-chlorophenylmethyl)propanamide
25
11f. Oil; ½aꢂD ¼ ꢀ33:6 (c 1.250, CHCl3); ee >99% (chiral
1
HPLC analysis); H NMR (300 MHz, CDCl3) 7.27–7.20
4.2.12. (S)-b-Azido-a-(p-fluorophenylmethyl)propanamide
(3H, m), 7.11–7.06 (1H, m), 5.72 (1H, br), 5.57 (1H, br),
3.60 (1H, dd, J = 12.1, 8.5 Hz), 3.42 (1H, dd, J = 12.1,
5.1 Hz), 2.93 (1H, dd, J = 13.6, 8.6 Hz), 2.77 (1H, dd,
25
11d. Mp 80–81 ꢁC; ½aꢂD ¼ ꢀ34:5 (c 2.495, CHCl3); ee
>99% (chiral HPLC analysis); 1H NMR (300 MHz,

2374
D.-Y. Ma et al. / Tetrahedron: Asymmetry 17 (2006) 2366–2376
J = 13.6, 6.3 Hz), 2.66–2.56 (1H, m); 13C NMR (75 MHz,
CDCl3) d 174.3, 140.2, 134.5, 130.0, 129.0, 127.15, 127.1,
52.4, 48.3, 35.7 ppm; IR (KBr) m 3324, 2930 (CONH2),
2102 (N3), 1668 cmꢀ1 (C@O); MS (ESI+) m/z 262.3
[M+2+Na]+, 260.9 [M+Na]+. Anal. Calcd for
C10H11N4OCl: C, 50.32; H, 4.65; N, 23.47. Found: C,
50.34; H, 4.59; N, 23.32.
4.2.21. (R)-b-Azido-a-(p-bromophenylmethyl)propanoic acid
25
12h. Oil; ½aꢂD ¼ ꢀ29:5 (c 1.220, CHCl3); ee 93.6% (chiral
HPLC analysis); 1H NMR (300 MHz, CDCl3) 7.44 (2H, d,
J = 8.4 Hz), 7.08 (2H, d, J = 8.4 Hz), 3.50 (2H, d,
J = 5.7 Hz), 3.04–2.99 (1H, m), 2.92–2.81 (2H, m); 13C
NMR (75 MHz, CDCl3) d 178.7, 136.4, 131.9, 130.7,
120.9, 50.9, 46.5, 34.2 ppm; IR (KBr) m 3089–2564
(COOH), 2105 (N3), 1711 (C@O) cmꢀ1; MS (EI) m/z (%)
285 (3) [M+2]+, 283 (3), 257 (4), 255 (4), 213 (59), 212
(61), 211 (73), 210 (74), 171 (47), 169 (47), 132 (100), 115
(37). Anal. Calcd for C10H10N3O2Br: C, 42.27; H, 3.55;
N, 14.79. Found: C, 42.31; H, 3.62; N, 14.58.
4.2.17.
(R)-b-Azido-a-(m-chlorophenylmethyl)propanoic
25
acid 12f. Oil; ½aꢂD ¼ ꢀ31:8 (c 1.130, CHCl3); ee >99%
(chiral HPLC analysis); 1H NMR (300 MHz, CDCl3)
9.23 (1H, br), 7.27–7.07 (4H, m), 3.50 (2H, d,
J = 5.5 Hz), 3.08–3.04 (1H, m), 2.93–2.81 (2H, m); 13C
NMR (75 MHz, CDCl3) d 178.5, 139.5, 134.5, 130.0,
129.1, 127.2, 127.15, 50.9, 46.4, 34.4 ppm; IR (KBr) m
3060–2569 (COOH), 2105 (N3), 1711 (C@O) cmꢀ1; MS
(EI) m/z (%) 240 (2) [M]+, 213 (6), 211 (15), 169 (24), 168
(28), 167 (93), 166 (100), 132 (80), 127 (24), 125 (84). Anal.
Calcd for C10H10N3O2Cl: C, 50.12; H, 4.21; N, 17.53.
Found: C, 49.76; H, 4.11; N, 17.13.
4.2.22. (ꢀ)-b-Azido-a-cyclohexylmethylpropanamide 11i.
25
Mp 82–83 ꢁC; ½aꢂD ¼ ꢀ28:2 (c 2.800, CHCl3); ee >99%
(chiral HPLC analysis); 1H NMR (300 MHz, CDCl3)
5.83 (1H, br), 5.70 (1H, br), 3.55 (1H, dd, J = 12.1,
8.9 Hz), 3.37 (1H, dd, J = 12.1, 4.8 Hz), 2.51–2.48 (1H,
m), 1.72–1.54 (6H, m), 1.31–1.18 (5H, m), 0.93–0.81 (2H,
m); 13C NMR (75 MHz, CDCl3) d 175.9, 53.4, 43.8, 37.6,
35.2, 33.6, 33.1, 26.4, 26.1 ppm; IR (KBr) m 3403, 3220
(CONH2), 2091 (N3), 1640 cmꢀ1 (C@O); MS (EI) m/z
(%) 182 (2) [Mꢀ28]+, 164 (15), 139 (9), 135 (5), 121
(100), 108 (17). Anal. Calcd for C10H18N4O: C, 57.12; H,
8.63; N, 26.64. Found: C, 57.23; H, 8.59; N, 26.41.
4.2.18. (S)-b-Azido-a-(o-chlorophenylmethyl)propanamide
25
11g. Mp 85–87 ꢁC; ½aꢂD ¼ ꢀ39:6 (c 2.575, CHCl3); ee
>99% (chiral HPLC analysis); 1H NMR (300 MHz, CDCl3)
7.39–7.33 (1H, m), 7.25–7.19 (3H, m), 6.12 (1H, br), 5.81
(1H, br), 3.64 (1H, dd, J = 12.0, 8.8 Hz), 3.41 (1H, dd,
J = 12.0, 4.6 Hz), 2.03–2.93 (2H, m), 2.86–2.80 (1H, m);
13C NMR (75 MHz, CDCl3) d 175.0, 135.8, 133.9, 131.6,
129.8, 128.5, 127.1, 52.3, 46.0, 34.1 ppm; IR (KBr) m 3390,
3197 (CONH2), 2103 (N3), 1665 cmꢀ1 (C@O); MS (EI) m/
z (%) 212 (5) [Mꢀ26]+, 210 (16), 203 (46), 177 (13), 175
(100). Anal. Calcd for C10H11N4OCl: C, 50.32; H, 4.65;
N, 23.47. Found: C, 50.42; H, 4.66; N, 23.44.
4.2.23. (+)-b-Azido-a-cyclohexylmethylpropanoic acid 12i.
25
Oil; ½aꢂD ¼ þ6:0 (c 4.300, CHCl3); ee 95.6% (chiral HPLC
analysis); 1H NMR (300 MHz, CDCl3) 3.54 (1H, dd,
J = 12.2, 8.2 Hz), 3.44 (1H, dd, J = 12.2, 5.2 Hz), 2.76–
2.72 (1H, m), 1.81–1.55 (6H, m), 1.44–1.08 (5H, m),
0.99–0.83 (2H, m); 13C NMR (75 MHz, CDCl3) d 180.2,
52.6, 42.7, 37.1, 35.2, 33.3, 32.9, 26.4, 26.0 ppm; IR
(KBr) m 3037–2555 (COOH), 2102 (N3), 1710 (C@O),
1450, 1274 cmꢀ1; MS (EI) m/z (%) 183 (9) [Mꢀ28]+, 154
(3), 140 (100). Anal. Calcd for C10H17N3O2: C, 56.85; H,
8.11; N, 19.89. Found: C, 56.90; H, 8.03; N, 20.10.
4.2.19. (R)-b-Azido-a-(o-chlorophenylmethyl)propanoic acid
25
12g. Oil; ½aꢂD ¼ ꢀ29:4 (c 2.855, CHCl3); ee >99% (chiral
1
HPLC analysis); H NMR (300 MHz, CDCl3) 10.83 (1H,
br), 7.43–7.38 (1H, m), 7.30–7.22 (3H, m), 3.59–3.54 (2H,
m), 3.26–3.20 (1H, m), 3.11–3.00 (2H, m); 13C NMR
(75 MHz, CDCl3) d 179.2, 135.4, 134.2, 131.5, 129.9,
128.6, 127.1, 51.3, 44.8, 32.8 ppm; IR (KBr) m 3059–2558
(COOH), 2104 (N3), 1712 (C@O) cmꢀ1; MS (EI) m/z (%)
213 (2) [Mꢀ26]+, 211 (6), 178 (22), 169 (5), 168 (10), 167
(20), 166 (29), 147 (22), 132 (100). Anal. Calcd for
C10H10N3O2Cl: C, 50.12; H, 4.21; N, 17.53. Found: C,
50.03; H, 4.15; N, 17.76.
4.2.24. (ꢀ)-b-Azido-a-cyclopropylmethylpropanamide 11j.
25
Mp 64–66 ꢁC; ½aꢂD ¼ ꢀ29:8 (c 1.945, CHCl3); ee 83.0%
(chiral HPLC analysis); 1H NMR (300 MHz, CDCl3)
6.06 (1H, br), 5.81 (1H, br), 3.63 (1H, dd, J = 12.1,
8.8 Hz), 3.45 (1H, dd, J = 12.1, 5.0 Hz), 2.55–2.46 (1H,
m), 1.67–1.58 (1H, m), 1.39–1.30 (1H, m), 0.75–0.70 (1H,
m), 0.53–0.46 (2H, m), 0.14–0.05 (2H, m); 13C NMR
(75 MHz, CDCl3) d 175.8, 52.7, 47.0, 35.1, 8.8, 4.8,
4.5 ppm; IR (KBr) m 3386, 3196 (CONH2), 2110 (N3),
1654 cmꢀ1 (C@O); MS (EI) m/z (%) 140 (17) [Mꢀ28]+,
126 (100). Anal. Calcd for C7H12N4O: C, 49.99; H, 7.19;
N, 33.31. Found: C, 49.78; H, 7.19; N, 32.98.
4.2.20. (S)-b-Azido-a-(p-bromophenylmethyl)propanamide
25
11h. Mp 75–76 ꢁC; ½aꢂD ¼ ꢀ29:1 (c 1.445, CHCl3); ee
>99% (chiral HPLC analysis); 1H NMR (300 MHz,
CDCl3) 7.44 (2H, d, J = 8.4 Hz), 7.08 (2H, d,
J = 8.4 Hz), 5.41 (2H, br), 3.61 (1H, dd, J = 12.2,
8.4 Hz), 3.43 (1H, dd, J = 12.2, 5.1 Hz), 2.91 (1H, dd,
J = 13.6, 8.8 Hz), 2.76 (1H, dd, J = 13.6, 6.2 Hz), 2.52–
2.62 (1H, m); 13C NMR (75 MHz, CDCl3) d 174.4, 137.1,
131.8, 130.6, 120.8, 52.4, 48.3, 35.5 ppm; IR (KBr) m
3386, 3196 (CONH2), 2116 (N3), 1645 cmꢀ1 (C@O); MS
(EI) m/z (%) 256 (36) [Mꢀ26]+, 254 (37), 239 (39), 238
(54), 237 (40), 236 (37), 226 (43), 211 (84), 210 (100), 209
(71), 208 (58), 171 (59), 158 (62), 130 (60). Anal. Calcd
for C10H11N4OBr: C, 42.42; H, 3.92; N, 19.79. Found: C,
42.13; H, 3.88; N, 19.73.
4.2.25. b-Azido-a-cyclopropylmethylpropanoic acid 12j.
25
Oil; ½aꢂD ¼ 0 (c 2.800, CHCl3); ee 58.6% (chiral HPLC
analysis); 1H NMR (300 MHz, CDCl3) 11.90 (1H, br),
3.65 (1H, dd, J = 12.2, 8.0 Hz), 3.56 (1H, dd, J = 12.2,
5.4 Hz), 2.80–2.71 (1H, m), 1.68–1.49 (2H, m), 0.81–0.68
(1H, m), 0.57–0.46 (2H, m), 0.13–0.08 (2H, m); 13C
NMR (75 MHz, CDCl3) d 180.4, 51.7, 45.8, 34.3, 8.4,
4.7, 4.5 ppm; IR (KBr) m 3081–2566 (COOH), 2104 (N3),
1711 (C@O) cmꢀ1; MS (EI) m/z (%) 141 (3) [Mꢀ28]+,
140 (5), 127 (46), 97 (31), 82 (38), 68 (100). Anal. Calcd

D.-Y. Ma et al. / Tetrahedron: Asymmetry 17 (2006) 2366–2376
2375
for C7H11N3O2: C, 49.70; H, 6.55; N, 24.84. Found: C,
49.75; H, 6.43; N, 24.83.
nol (5 ml) for 12 h. After removal of the ethanol under
vacuum followed by silica gel column chromatography
eluting with a mixture of petroleum ether and acetone
(1.5:1), diethyl 1-(2S-carbamoyl-3-phenyl)propyl-1H-
4.2.26. (ꢀ)-a-Azidomethylpentanamide 11k. Mp 63–
25
65 ꢁC; ½aꢂD ¼ ꢀ12:2 (c 1.880, CHCl3); ee 65.0% (chiral
[1,2,3]triazole-4,5-dicarboxylate 14 (337 mg, 90%) was ob-
25
1
HPLC analysis); H NMR (300 MHz, CDCl3) 6.07 (1H,
tained as an oil: ½aꢂD ¼ ꢀ72:6 (c 1.350, CHCl3); 1H
br), 5.80 (1H, br), 3.58 (1H, dd, J = 12.1, 8.8 Hz), 3.39
(1H, dd, J = 12.1, 4.9 Hz), 2.45–2.34 (1H, m), 1.69–1.58
(1H, m), 1.45–1.34 (3H, m), 0.93 (3H, t, J = 7.2 Hz); 13C
NMR (75 MHz, CDCl3) d 175.9, 53.0, 46.4, 32.2, 20.4,
14.0 ppm; IR (KBr) m 3407, 3332, 3294, 3209 (CONH2),
2107 (N3), 1656 cmꢀ1 (C@O); MS (EI) m/z (%) 128 (25)
[Mꢀ28]+, 114(10), 99 (60), 82 (36), 72 (100). Anal. Calcd
for C6H12N4O: C, 46.14; H, 7.74; N, 35.87. Found: C,
46.13; H, 7.83; N, 35.72.
NMR (300 MHz, CDCl3) 7.29–7.18 (5H, m), 5.95 (1H,
br), 5.61 (1H, br), 4.92 (1H, dd, J = 13.7, 9.0 Hz), 4.55
(1H, dd, J = 13.7, 5.4 Hz), 4.43 (2H, q, J = 7.1 Hz), 4.38
(2H, q, J = 7.1 Hz), 3.46–3.36 (1H, m), 3.04 (1H, dd,
J = 13.7, 8.7 Hz), 2.83 (1H, dd, J = 13.7, 6.4 Hz), 1.39
(3H, t, J = 7.3 Hz), 1.30 (3H, t, J = 7.6 Hz); 13C NMR
(75 MHz, CDCl3) d 173.6, 160.0, 158.5, 139.6, 137.6,
131.2, 128.9, 128.7, 126.9, 63.1, 61.8, 51.1, 48.5, 36.6,
14.1, 13.9 ppm; IR (KBr) m 3333, 3195 (CONH2), 1732,
1677 (C@O) cmꢀ1; MS (EI) m/z (%) 374 (5) [M]+, 301
(13), 161 (60), 160 (79), 143 (84), 117 (85), 116 (74), 115
(92), 91 (100). Anal. Calcd for C18H22N4O5: C, 57.75; H,
5.92; N, 14.96. Found: C, 57.91; H, 6.02; N, 15.19.
25
4.2.27. (ꢀ)-a-Azidomethylpentanoic acid 12k. Oil; ½aꢂD
¼
ꢀ2:6 (c 1.175, CHCl3); ee 75.0% (chiral HPLC analysis);
1H NMR (300 MHz, CDCl3) 11.50 (1H, br), 3.57 (1H,
dd, J = 12.2, 8.2 Hz), 3.46 (1H, dd, J = 12.2, 5.3 Hz),
2.68–2.59 (1H, m), 1.74–1.62 (1H, m), 1.59–1.49 (1H, m),
1.48–1.33 (2H, m), 0.95 (3H, t, J = 7.2 Hz); 13C NMR
4.6. Preparation of 1-[(2R-hydroxycarbonyl-3-phenyl)-
propyl]-4-phenyl-1H-1,2,3-triazole 15
(75 MHz, CDCl3)
d 179.8, 52.1, 45.0, 31.5, 20.1,
13.9 ppm; IR (KBr) m 3037–2551 (COOH), 2103 (N3),
1710 (C@O) cmꢀ1; MS (EI) m/z (%) 129 (3) [Mꢀ28]+,
114 (8), 100 (11), 87 (19), 73 (100), 55 (35). Anal. Calcd
for C6H11N3O2: C, 45.85; H, 7.05; N, 26.74. Found: C,
45.86; H, 6.98; N, 26.46.
To a mixture of (R)-12a (205 mg, 1 mmol), tert-butanol
(2.5 ml), and water (2 ml) were added consecutively phenyl-
acetylene (1.5 mmol), aqueous sodium ascorbate (100 ll,
1 M), and aqueous copper(II) sulfate (100 ll, 0.1 M). The
resulting mixture was stirred at room temperature for
2 h. Water (25 ml) was added and the mixture extracted
with ethyl acetate (3 · 15 ml). After drying over MgSO4
and concentration, the residue was passed through a silica
gel column eluted with a mixture of petroleum ether and
acetone (1.5:1) to afford 1-[(2R-hydroxycarbonyl-3-
4.3. Preparation of (S)-b-azido-a-benzylpropanoic acid 12a
A mixture of (S)-11a (182 mg, ee >99.5%) in hydrochloric
acid (6 M, 8 ml) was stirred at 55 ꢁC for 43 h. Water
(60 ml) was added and the mixture was extracted with
dichloromethane (3 · 20 ml). After drying over MgSO4
and removal of the solvent under vacuum, (S)-b-azido-a-
phenyl)propyl]-4-phenyl-1H-1,2,3-triazole 15 (310 mg,
25
100%) as a white powder: mp 141–143 ꢁC; ½aꢂD ¼ þ7:2 (c
1.955, MeOH); 1H NMR (300 MHz, DMSO-d6) 12.6
(1H, br), 8.54 (1H, s), 7.84 (2H, d, J = 8.0 Hz), 7.45 (2H,
t, J = 7.6 Hz), 7.35–7.20 (6H, m), 4.62 (1H, dd, J = 13.8,
8.4 Hz), 4.51 (1H, dd, J = 13.7, 5.6 Hz), 3.33 (1H, quin,
J = 6.8 Hz), 2.98–2.84 (2H, m); 13C NMR (75 MHz,
DMSO-d6) d 173.4, 146.1, 138.1, 130.7, 128.91, 128.86,
128.3, 127.8, 126.5, 125.1, 121.9, 50.5, 47.2, 35.0 ppm; IR
benzylpropanoic acid (S)-12a (176 mg, 96%) was obtained
25
as colorless liquid: ½aꢂD ¼ þ31:1 (c 2.950, CHCl3), ee
>99.5% (chiral HPLC analysis).
4.4. Synthesis of (S)- and (R)-a-benzyl-b-amino acids
(KBr) m 3137–2521 (COOH), 1715, 1702 (C@O) cmꢀ1
;
(S)-12a (151 mg, 0.74 mmol, ee >99.5%) was dissolved in
methanol (15 ml) followed by the addition of 10% Pd/C cat-
alyst (74 mg). The mixture was then stirred at room temper-
ature under hydrogen atmosphere for 3 h. Water (15 ml)
was then added and the mixture was stirred for another
30 min. Filtration and concentration gave (S)-(ꢀ)-a-benz-
yl-b-aminopropanoic acid (S)-(ꢀ)-13 (122 mg, 93%) as a
white powder: mp 209–212 ꢁC (lit.22 mp 224–225 ꢁC);
MS (EI) m/z (%) 307 (6) [M]+, 278 (5), 145 (100). Anal.
Calcd for C18H17N3O2: C, 70.34; H, 5.58; N, 13.67. Found:
C, 70.13; H, 5.66; N, 13.77.
Acknowledgements
25
25
½aꢂD ¼ ꢀ17:3 (c 1.850, 1 M HCl) {lit.22 ½aꢂD ¼ ꢀ11:0 (c
We thank the State Major Fundamental Research Program
(2003CB716005), the National Natural Science Founda-
tion of China and the Chinese Academy of Sciences for
financial support. We also thank Mr. M. Gao for technical
assistance.
1
1.000, 1 M HCl)]}; H NMR (300 MHz, D2O) 7.34–7.23
(5H, m), 3.08–2.95 (3H, m), 2.85–2.80 (2H, m); IR (KBr)
m 3420 (CONH2), 3027–2628 (COOH), 1633 (C@O) cmꢀ1
.
25
Hydrogenation of (R)-12a gave (R)-(+)-13: ½aꢂD ¼ þ16:9
25
(c 2.250, 1 M HCl) [lit.22 ½aꢂD ¼ þ11:3 (c 1.000, 1 M HCl)].
4.5. Preparation of diethyl 1-[(2S-carbamoyl-3-phenyl)-
propyl]-1H-[1,2,3]triazole-4,5-dicarboxylate 14
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