Dynamic kinetic resolution of 2-oxocycloalkanecarbonitriles: Chemoenzymatic syntheses of optically active cyclic β- and γ-amino alcohols

Article abstract of DOI:10.1021/jo0257288

A series of fungi and yeasts have been tested for the stereoselective bioreduction of 2-oxocycloalkanecar-bonitriles, 1. The yeast Saccharomyces montanus CBS 6772 yielded the corresponding cis-hydroxy nitriles, 2, in >90% ee and de and in high chemical yields. Through simple and efficient procedures, they were transformed into optically active 2-amino and 2-aminomethyl cycloalkanols.

Full text of DOI:10.1021/jo0257288

SCHEME 1
Dyn a m ic Kin etic Resolu tion of
2-Oxocycloa lk a n eca r bon itr iles:
Ch em oen zym a tic Syn th eses of Op tica lly
Active Cyclic â- a n d γ-Am in o Alcoh ols
J uan R. Dehli and Vicente Gotor*
Departamento de Quı´mica Orga´nica e Inorga´nica,
Universidad de Oviedo, c/ J ulia´n Claverı´a, 8,
E-33006 Oviedo, Spain
Continuing this study and encouraged by the high
enantio- and diastereoselectivity of these processes, we
decided to extend the methodology to 2-oxocycloalkan-
ecarbonitriles, 1, as suitable precursors of cyclic amino
alcohols. The high acidity of the R-hydrogen10 would
cause racemization of the substrate in water and allow
for a dynamic kinetic resolution (see Scheme 1), as has
been previously described for â-keto esters,11,12 â-keto
amides,13 and â-diketones.14
The importance of this acidic R-hydrogen must be
emphasized, since â-keto nitriles fully substituted at the
R-position do not racemize under the biotransformation
conditions and are reduced through a parallel kinetic
resolution, therefore yielding both enantioenriched dia-
stereomers of the corresponding â-hydroxy nitriles con-
taining a quaternary stereocenter.15
The bioreduction of R-monosubstituted â-keto nitriles
has been scarcely reported in the literature: Itoh de-
scribed that baker’s yeast-mediated bioreduction of acy-
clic substrates resulted in a nearly equimolar mixture of
diastereomers in most cases.16 On the other hand, Azerad
studied the microbial reduction of a couple of 2-cyano-1-
tetralones.17
The selection of compounds 1 was made on the basis
of its ready availability from inexpensive alkanedinitriles
through a Thorpe-Ziegler reaction,18 which would make
this a good strategy for the preparation of the above-
mentioned amino alcohols.
vgs@sauron.quimica.uniovi.es
Received March 18, 2002
Abstr a ct: A series of fungi and yeasts have been tested
for the stereoselective bioreduction of 2-oxocycloalkanecar-
bonitriles, 1. The yeast Saccharomyces montanus CBS 6772
yielded the corresponding cis-hydroxy nitriles, 2, in >90%
ee and de and in high chemical yields. Through simple and
efficient procedures, they were transformed into optically
active 2-amino and 2-aminomethyl cycloalkanols.
The preparation of optically active amino alcohols has
received considerable attention in recent years due to
their importance in both medicinal chemistry1 and asym-
metric synthesis.2 In this context, cyclic compounds are
of the utmost importance because of their conformational
restrictions.
To date, several enzymatic procedures for the kinetic
resolution of racemic mixtures of 2-aminocycloalkanols3,4
and 2-aminomethylcycloalkanols5 have been described.
However, they suffer from the main disadvantage of this
kind of resolutions: the theoretical impossibility of
reaching 100% of both chemical yield and enantiomeric
excess. To overcome this limitation, a great effort has
been devoted to create processes that afford the product
with the same high enantiomeric purity but in signifi-
cantly improved yield.6
We have been interested in the bioreduction of R-un-
substituted â-keto nitriles by whole cells7 as potential
precursors of optically active γ-amino alcohols. In this
study, we also found and optimized a competing reaction,
which introduced an alkyl chain at the R-position,
therefore yielding â-hydroxy nitriles with two contiguous
chiral centers.8,9
To confirm our hypothesis of easy racemization of the
substrates, the pKa of compound 1a was measured by
potentiometry, in a 0.1 mol/L NMe4Cl solution at 298 K,
obtaining a value as low as 7.84. This high acidity of
â-keto nitriles (considerably higher than that of the
analogous â-keto esters) had been previously reported.10
The results obtained in the bioreduction of 1a with
several fungal and yeast strains at an analytical scale
are summarized in Table 1. With fungi, a low stereose-
lectivity was observed. In contrast, when yeasts were
* To whom correspondence should be addressed. Phone/Fax: +34
985 103448.
(1) Kordik, C. P.; Reitz, A. B. J . Med. Chem. 1999, 42, 181-202.
(2) Ager, D. J .; Prakash, I.; Schaad, D. R. Chem. Rev. 1996, 96, 835-
875.
(10) Kuehne, M. E.; Nelson, J . A. J . Org. Chem. 1970, 35, 161-170.
(11) Buisson, D.; Azerad, R. Tetrahedron Lett. 1986, 27, 2631-2634.
(12) Danchet, S.; Bigot, C.; Buisson, D.; Azerad, R. Tetrahedron:
Asymmetry 1997, 8, 1735-1739.
(3) Maestro, A.; Astorga, A.; Gotor, V. Tetrahedron: Asymmetry
1997, 8, 3153-3159.
(13) Quiro´s, M.; Rebolledo, F.; Gotor, V. Tetrahedron: Asymmetry
1999, 10, 473-486.
(4) Luna, A.; Astorga, C.; Fu¨lo¨p, F.; Gotor, V. Tetrahedron: Asym-
metry 1998, 9, 4483-4487.
(14) J i, A.; Wolberg, M.; Hummel, W.; Wandrey, C.; Mu¨ller, M.
Chem. Commun. 2001, 57-58.
(5) Ka´ma´n, J .; Forro´, E.; Fu¨lo¨p, F. Tetrahedron: Asymmetry 2001,
12, 1881-1886.
(15) Dehli, J . R.; Gotor, V. J . Org. Chem. 2002, 67, 1716-1718.
(16) Itoh, T.; Fukuda, T.; Fujisawa, T. Bull. Chem. Soc. J pn. 1989,
62, 3851-3855.
(6) Faber, K. Chem. Eur. J . 2001, 7, 5004-5010.
(7) Dehli, J . R.; Gotor, V. Tetrahedron: Asymmetry 2000, 11, 3693-
3700.
(17) Mehmandoust, M.; Buisson, D.; Azerad, R. Tetrahedron Lett.
1995, 36, 6461-6462.
(8) Gotor, V.; Dehli, J . R.; Rebolledo, F. J . Chem. Soc., Perkin Trans.
1 2000, 307-309.
(9) Dehli, J . R.; Gotor, V. Tetrahedron: Asymmetry 2001, 12, 1485-
1492.
(18) Davis, B. R.; Garratt, P. J . Acylation of Esters, Ketones and
Nitriles. In Comprehensive Organic Synthesis; Trost, B. M., Ed.;
Pergamon Press: Oxford, 1991; Vol. 2, pp 848-852.
10.1021/jo0257288 CCC: $22.00 © 2002 American Chemical Society
Published on Web 08/15/2002
6816
J . Org. Chem. 2002, 67, 6816-6819

TABLE 1. Bior ed u ction of 1a by Sever a l Micr obia l
Str a in s a t a n An a lytica l Sca lea
(up to 93%). Cells were resuspended in distilled water
instead of phosphate buffer to facilitate the downstream
processing of a hypothetical industrial application.19 Once
again, substrate concentrations higher than 1 g/L led to
incomplete conversion. An insufficient ratio of biocatalyst
to substrate rather than inhibition by substrate or
product was invoked, since a 10-fold concentration of the
cells allowed us to carry out the biotransformation at 10
g/L of 1b.
We carried out the gram-scale bioreduction under the
following conditions: 1 g of 1b and 1 mL of ethanol were
added to cells grown in 1 L of medium and resuspended
in 100 mL of distilled water. After 1 day, 2b was obtained
in 85% chemical yield and 93% ee. A space-time yield
of 8.6 g L-1 day-1 was calculated.
absolute
cis:transb,c eecis (%)b configuration
microorganism
baker’s yeast
Saccharomyces montanus
NRRL 6772
95:5
96:4
90
93
1S,2S
1S,2S
1R,2R
1S,2S
1S,2S
Curlvularia lunata
CECT 2130
Mortierella isabellina
NRRL 1757
Beauveria bassiana
ATCC 7159
53:47
65:35
50:50
41
48
21
The fact that the â-hydroxy nitriles, 2, obtained in the
bioreductions had a cis configuration and very high ee
values made them very tempting building blocks for the
preparation of amino alcohols. It must be emphasized
that, whereas for the preparation the trans-hydroxy
nitriles many strategies have been developed,20,21 very
few examples have been described for the cis isomers.22,23
Furthermore, the bioreduction of structurally related
2-oxocyclopentanecarboxamide with Mortierella isabel-
lina yielded mainly the trans isomer, and with B.
bassiana, the cis isomer only with low ee.13 In the course
of our work, a synthesis of cis amino alcohols from the
corresponding â-hydroxy esters obtained by baker’s yeast-
mediated reduction has been described.24 It must be also
mentioned that the bioreduction of analogous â-keto
esters by S. montanus yielded mainly the cis diastereo-
mers, but in lower diastereomeric excess (ca. 60%).11
The pathway followed for the preparation of 2-ami-
nocycloalkanols, 5, is outlined in Scheme 2. Acidic hy-
drolysis of the nitrile group at 50 °C yielded the corre-
sponding carboxylic amide, 3, in nearly quantitative
yield. Hofmann rearrangement with iodobenzene diac-
etate25,26 at room temperature yielded the oxazolidinones
4. Epimerization at the stereogenic center R to the amide
group was excluded by the high yield (over 90%), together
with NMR and TLC analysis of the crude product, and
the ee was confirmed by chiral GC. Finally, hydrolysis
of 4 by LiOH in a mixture of water and MeOH yielded
the â-amino alcohols, which were isolated as their N-Cbz
derivatives, 5, in 65-70% global yield.
a
Typically, the substrate (35 mg) and ethanol (350 µL) were
added to a 35 mL culture. Determined by chiral GC. c The ee and
the absolute configuration of the trans isomer have not been
determined.
b
TABLE 2. Bior ed u ction of 1b by Sever a l Micr obia l
Str a in s a t a n An a lytica l Sca lea
eecis
absolute
eetrans
microorganism
baker’s yeast
S. montanus NRRL 6772
C. lunata CECT 2130
M. isabellina NRRL 1757
B. bassiana ATCC 7159
cis:transb (%)b configuration (%)b,c
87:13
95:5
70:30
71:29
30:70
65 1S,2S
87 1S,2S
17 1S,2S
71 1S,2S
72 1S,2S
26
8
46
60
89
a
Typically, the substrate (35 mg) and ethanol (350 µL) were
added to a 35 mL culture. Determined by chiral GC. c Absolute
configuration of the trans isomer has not been determined.
b
used, a very high stereoselectivity occurred: with both
strains, cis-2a was obtained as the major diastereomer
and in high enantiomeric excess.
With Saccharomyces montanus, the most promising
strain, some modifications of the reaction conditions were
made to optimize the process for an efficient preparative
scale: the use of resting cells instead of growing cells
resulted in a sharp decrease in the stereoselectivity. On
the contrary, the addition of the substrate at an early
stage of the culture growth (8 h after inoculation) resulted
in a higher cis:trans ratio (99:1) as well as eecis (97%).
However, and despite our efforts, substrate concentra-
tions higher than 1 g/L resulted in incomplete conver-
sions.
When this was repeated at the gram scale, using 1 g
of 1a , 10 mL of ethanol, and 1 L of culture, we obtained
2a in 89% chemical yield and 97% ee after removing the
traces of the trans isomer by column chromatography.
The same screening for a suitable biocatalyst was
carried out for the bioreduction of the six-membered ring
(see Table 2).
On the other hand, the reduction of the nitrile group
by LiAlH4 in anhydrous Et2O yielded the corresponding
γ-amino alcohols in excellent yields, which were also
isolated as their N-Cbz derivatives, 6 (Scheme 3). As for
compounds 5, neither by TLC nor by NMR of the crude
reaction was the other diastereomer detected.
(19) See, for example: Genzel, Y.; Archelas, A.; Broxterman, Q. B.;
Schulze, B.; Furstoss, R. J . Org. Chem. 2001, 66, 538-543.
(20) Schaus, S. E.; J acobsen, E. N. Org. Lett. 2000, 2, 1001-1004.
(21) Yamasaki, S.; Kanai, M.; Shibasaki, M. J . Am. Chem. Soc. 2001,
123, 1256-1257.
(22) For racemic ones, see: Wade, P. A.; Hinney, H. R. J . Am. Chem.
Soc. 1979, 101, 1319-1320.
(23) For the enzymatic kinetic resolution of both cis and trans
isomers, see: Forro´, E.; Lundell, K.; Fu¨lo¨p, F.; Kanerva, L. T.
Tetrahedron: Asymmetry 1997, 8, 3095-3099.
(24) Bertau, M.; Bu¨rli, M.; Hungerbu¨hler, E.; Wagner, P. Tetrahe-
dron: Asymmetry 2001, 12, 2103-2107.
(25) Zhang, L.-H.; Kauffman, G. S.; Pesti, J . A.; Yin, J . J . Org. Chem.
1997, 62, 6918-6920.
Again, the best results were obtained with the yeast
S. montanus. In this case, the use of resting cells instead
of growing cells resulted in a slight increase in the eecis
(26) Garc´ıa-Urdiales, E.; Rebolledo, F.; Gotor, V. Tetrahedron:
Asymmetry 1999, 10, 721-726.
J . Org. Chem, Vol. 67, No. 19, 2002 6817

SCHEME 2
Syn th eses of th e 2-Oxocycloa lk a n eca r bon itr iles, 1. To
a suspension of NaH (1.3 g, 55 mmol) in 100 mL of THF was
added 50 mmol of the corresponding alkanedinitrile, and the
mixture was refluxed until the substrate disappeared (TLC
monitoring, eluent 2:1 hexane/AcOEt). Then, the reaction mix-
ture was allowed to reach room temperature; the reaction was
quenched with 30 mL of water, and the mixture was extracted
with Et2O. After drying and elimination of the solvent, the
enamine formed was hydrolyzed at room temperature with 50
mL of 3 N H2SO4, extracted again with Et2O, and dried and the
solvent removed on a rotovapor. The residual oil was further
purified by bulb-to-bulb distillation.
Syn th esis of Ster eoisom er ic Mixtu r es of 2-Hyd r oxycy-
cloa lk a n eca r bon itr iles. To a solution of 1 mmol of 1 in 5 mL
of EtOH was added 25 mg (0.7 mmol) of NaBH4, and the mixture
was shaken at room temperature overnight. After partial
elimination of the solvent, addition of water, and extraction with
Et2O, a pale yellowish oil was obtained, which was used without
further purification as a standard for chiral GC analyses
(conditions: 100 °C, 15 min; 1 °C/min until 170 °C). tR (min):
(1S,2S)-2a , 34.9; (1R,2R)-2a , 36.9; trans-2a , 42.4 (both enanti-
omers); (1S,2S)-2b, 46.6; (1R,2R)-2b, 47.5; trans-2b, 49.2 and
50.9.
Gen er a l P r oced u r e for Cu ltu r es of S. m on ta n u s CBS
6772. A loop of a solid culture of S. montanus from an agar plate
was sown into 35 mL of liquid medium [composed of yeast
extract (0.3%), malt extract (0.3%), D-glucose (1%), and bac-
topeptone (0.5%) in distilled water]. After the culture had grown
for over 60 h (rotatory shaker, 28 °C, 200 rpm), 5 mL of it were
used to inoculate 1 L of fresh medium, which was cultured under
the same conditions.
Bior ed u ction w ith Gr ow in g Cells. 2-Oxocyclopentanecar-
bonitrile (1 g), 1a , and 10 mL of EtOH were added to growing
cells of S. montanus (grown for 8 h in 1 L of medium), and the
biotransformation was carried out at 28 °C and 200 rpm. After
4 days, no more substrate was left (TLC monitoring), and the
culture was continuously extracted with CH2Cl2 over 12 h. Flash
chromatography (3:1 eluent hexane/Et2O) of the crude reaction
yielded 0.91 g of (1S,2S)-2a .
SCHEME 3
Although Kanerva and co-workers have recently de-
veloped a method for the enzymatic resolution of both
cis-2-hydroxycycloalkanenitriles, they noticed an impu-
rity affecting the value of the optical rotations, as well
as the spectral data. However, the values reported for
the trans isomers were incompatible with those obtained
in this work.23 The cis relative configuration of 2b was
confirmed by comparison of its 1H NMR spectral data
with those already published for the compound obtained
by syn-cyanohydroxylation of cyclohexene.22
Optically active 3a and 4a have also been described,
but in only 51% ee.13 On the other hand, â-amino alcohols,
5, have been obtained in high ee values.4 Taken all
together, and after discarding epimerization throughout
the processes (see above), we could unambiguously assign
the configuration of all the products reported herein.
In summary, the enantio- and diastereoselective biore-
duction of 2-oxocycloalcanecarbonitriles, 1, has been
accomplished by whole cells of the yeast S. montanus.
In the case of 1b, resting cells have been concentrated
to work at a higher substrate concentration. The optically
active â-hydroxy nitriles have been shown to be suitable
building blocks for the preparation of â- and γ-amino
alcohols through very efficient procedures. Due to their
cis relative configuration, this methodology complements
our previously reported procedure for the synthesis of
trans-2-aminomethyl and 2-aminocyclopentanol.
(1S,2S)-2-Hyd r oxycyclop en ta n eca r bon itr ile, 2a : yield
89%, colorless oil; [R]D20 +6.0 (c 1.0, CH2Cl2); ee 97%; IR ν (cm-1
)
Exp er im en ta l Section
2245, 3426; 1H NMR δ (ppm) 1.55-2.25 (m, 6H), 2.74 (m, 1H,
CH-CN), 3.0 (bs, 1H, OH), 4.4 (m, 1H, CH-O); 13C NMR δ (ppm)
21.8, 27.8, 33.4 (CH2), 36.4 (CH-CN), 73.4 (CH-O), 120.4 (CN);
ESIMS m/z 134 (M + Na)+. Anal. Calcd for C6H9NO: C, 64.84;
H, 8.16; N, 12.60. Found: C, 64.59; H, 8.25; N, 12.51.
Gen er a l. Fungi and yeasts were obtained from the corre-
sponding culture collections, except baker’s yeast type II, which
was acquired from Sigma. THF and Et2O were distilled over
sodium and stored under nitrogen. Precoated TLC plates of silica
gel 60 F254 were used, while for column chromatography silica
gel 60/230-400 mesh was applied. 1H and 13C NMR spectra were
carried out in CDCl3, unless otherwise stated. Mass spectra were
recorded using electrospray (40 V) as an ionization source.
Diastereomeric ratios and ee values were determined by GC
analyses using a Rt-âDEXse (30 m × 0.25 mm, Restek) capillary
column and nitrogen as the carrier gas (15 psia).
P oten tr iom etr ic Titr a tion . A Metrohm 702 titrimeter was
used, and the reference electrode was an Ag/AgCl electrode in
saturated aqueous KCl. The cell was thermostated at 298 ( 0.1
K and the solution stirred, and the measurements were per-
formed under nitrogen. The pKa value was determined by
titration with 0.1 N NaOH of a solution containing 10-3 M of
compound 1a in the presence of Me4NCl (0.1 M). The measure-
ments were carried out twice, and the data analysis was
performed with the computer program SUPERQUAD.27
Bior ed u ction w ith Restin g Cells. 2-Oxocyclohexanecarbo-
nitrile (1 g), 1b, and 1 mL of EtOH were added to cells of S.
montanus (grown for 36 h in 1 L of medium, centrifuged, and
resuspended in 100 mL of distilled water), and the biotransfor-
mation was carried out at 28 °C and 200 rpm. After 48 h, no
more substrate was left (TLC monitoring), and the culture was
continuously extracted with CH2Cl2 over 12 h. Flash chroma-
tography (eluent 3:1 hexane/Et2O) of the crude reaction yielded
0.86 g of (1S,2S)-2b.
(1S,2S)-2-Hydr oxycycloh exan ecar bon itr ile, 2b: yield 85%,
20
colorless oil; [R]D -26.9 (c 1.0, CH2Cl2); ee 93%; IR ν (cm-1
)
2244, 3425; 1H NMR δ (ppm) 1.25-1.4 (m, 1H), 1.5-1.9 (m, 6H),
1.95-2.1 (m, 1H), 2.43 (bs, 1H, OH), 3.0 (m, 1H, CH-CN), 3.8
(m, 1H, CH-O); 13C NMR δ (ppm) 21.8, 22.5, 26.4, 31.6 (CH2),
36.0 (CH-CN), 68.4 (CH-O), 120.2 (CN); ESIMS m/z 148 (M +
Na)+. Anal. Calcd for C7H11NO: C, 67.17; H, 8.86; N, 11.19.
Found: C, 67.01; H, 9.02; N, 11.07.
Gen er a l P r oced u r e for H yd r olyses of t h e â-H yd r oxy
Nitr iles 2. The corresponding nitrile 2 (1 mmol) was solved in
(27) Gans, P.; Sabatini, A.; Vacca, A. J . Chem. Soc., Dalton Trans.
1985, 1195-1200.
6818 J . Org. Chem., Vol. 67, No. 19, 2002

2 mL of concentrated HCl and the solution shaken at 50 °C for
2 h. The solution was placed on an ice bath, and 0.7 g NaOH
was added and then NaHCO3 until neutralization. Then, the
solution was continuously extracted with AcOEt for 6 h, and
after purification by flash chromatography (1:3 eluent hexane/
AcOEt), the corresponding amide 3 was obtained.
(m, 1H, CH-O), 5.09 (s, 2H, CH2-O), 5.27 (m, 1H, NH), 7.37
(m, 5H, arom); 13C NMR δ (ppm) 20.0, 28.9, 32.4 (CH2), 55.7
(CH-N), 66.7 (CH2-O), 72.5 (CH-O), 128.0, 128.4 (CHarom),
136.3 (Carom), 156.2 (CO); ESIMS m/z 258 (M + Na)+. Anal. Calcd
for C13H17NO3: C, 66.36; H, 7.28; N, 5.95. Found: C, 66.33; H,
7.35; N, 5.81.
(1R,2S)-2-Hyd r oxycyclop en ta n eca r boxa m id e, 3a : yield
96%, white solid; mp 100-101 °C; [R]D20 +29.3 (c 1.7, EtOH); ee
97%; IR ν (cm-1) 1673; 1H NMR (CD3OD) δ (ppm) 1.75-2.25
(m, 6H), 2.78 (m, 1H, CH-CO), 4.57 (m, 1H, CH-O); 13C NMR
(CD3OD) δ (ppm) 23.6, 28.4, 36.2 (CH2), 52.0 (CH-CO), 76.1
(CH-O), 180.3 (CO); ESIMS m/z 152 (M + Na)+. Anal. Calcd
for C6H11NO2: C, 55.80; H, 8.58; N, 10.84. Found: C, 55.52; H,
8.78; N, 10.70.
(1R,2S)-2-Hyd r oxycycloh exa n eca r boxa m id e, 3b: yield
94%, white solid; mp 121-122 °C; [R]D20 +24.1 (c 1.0, EtOH); ee
93%; IR ν (cm-1) 1670; 1H NMR (CD3OD) δ (ppm) 1.45-2.2 (m,
8H), 2.54 (ddd, 1H, CH-CO, J ) 2.6, 3.7, 11.6 Hz), 4.33 (m, 1H,
CH-O); 13C NMR (CD3OD) δ (ppm) 20.9, 25.2, 26.0, 33.3 (CH2),
48.4 (CH-CO), 68.2 (CH-O), 181.0 (CO); ESIMS m/z 166 (M +
Na)+. Anal. Calcd for C7H13NO2: C, 58.72; H, 9.15; N, 9.78.
Found: C, 58.68; H, 9.31; N, 9.65.
Hofm a n n Rea r r a n gem en t of th e Am id es 3. Iodobenzene
diacetate (1.3 mmol) was added to a solution of the corresponding
amide 3 (1 mmol) in 2.5:1 THF/MeOH (5 mL). The mixture was
stirred at room temperature until the substrate disappeared
(TLC monitoring, 2 h). Then, the solvents were removed under
vacuum, and the resulting residue was purified by flash chro-
matography (3:2 eluent hexane/AcOEt).
Ben zyl (1R,2S)-N-(2-Hyd r oxycycloh exyl)ca r ba m a te, 5b:
yield 73%, white solid; mp 51-52 °C; [R]D20 +32.5 (c 1.7, EtOH);
ee 93%; IR ν (cm-1) 1715; 1H NMR δ (ppm) 1.3-1.75 (m, 8H),
2.16 (bs, 1H, OH), 3.65 (m, 1H, CH-N), 3.94 (m, 1H, CH-O),
5.08 (s, 2H, CH2-O), 5.25 (m, 1H, NH), 7.35 (m, 5H, arom); 13
C
NMR δ (ppm) 19.7, 23.6, 27.2, 31.5 (CH2), 52.4 (CH-N), 66.6
(CH2-O), 68.9 (CH-O), 128.0, 128.1, 128.4 (CHarom), 136.3
(Carom), 156.1 (CO); ESIMS m/z 272 (M + Na)+. Anal. Calcd for
C
14H19NO3: C, 67.45; H, 7.68; N, 5.62. Found: C, 67.28; H, 7.89;
N, 5.49.
Red u ction of Nitr iles 2. To a solution of the corresponding
nitrile 2 (1 mmol) in anhydrous THF (5 mL) at 0 °C was added
an excess of LiAlH4 (5 mmol), and the suspension was allowed
to reach room temperature with stirring. After 1 h, the reaction
was quenched with water (1 mL) and the mixture extracted
several times with Et2O. Solvent was removed on a rotovapor,
and to the residual oil were added Na2CO3 (1.2 mmol), water (2
mL), and benzyl chloroformate (1.2 mmol) at 0 °C. The reaction
mixture was allowed to reach room temperature and shaken
overnight. After extraction with CH2Cl2, the product was isolated
by column chromatography (eluent 2:1 hexane/AcOEt).
Ben zyl (1S,2S)-N-[(2-Hyd r oxycyclop en tyl)m eth yl]ca r -
20
ba m a te, 6a : yield 91%, white solid; mp 54-55 °C; [R]D +7.3
(3a R,6a S)-P er h yd r ocyclop en ta [d ]oxa zol-2-on e, 4a : yield
(c 1.2, CHCl3); ee 97%; IR ν (cm-1) 1703; 1H NMR δ (ppm) 1.3-
1.9 (m, 7H), 3.1 (m, 1H, CHH-N), 3.3-3.7 (m, 2H, CHH-N and
OH), 4.12 (m, 1H, CH-O), 5.10 (s, 2H, CH2-O), 5.25 (bs, 1H,
NH), 7.34 (m, 5H, arom); 13C NMR δ (ppm) 21.8, 26.2, 33.8 (CH2),
40.3 (CH2-N), 47.6 (CH), 66.9 (CH2-O), 72.3 (CH-O), 128.0,
128.1, 128.4 (CHarom), 136.2 (Carom), 157.6 (CO); ESIMS m/z 272
(M + Na)+. Anal. Calcd for C14H19NO3: C, 67.45; H, 7.68; N,
5.62. Found: C, 67.21; H, 7.75; N, 5.52.
20
93%, white solid; mp 129-130 °C; [R]D -44.4 (c 1.1, CHCl3);
1
ee 97%; IR ν (cm-1) 1753, 3459; H NMR δ (ppm) 1.5-1.85 (m,
5H), 2.05-2.1 (m, 1H), 4.26 (m, 1H, CH-N), 5.04 (m, 1H, CH-
O), 6.39 (bs, 1H, NH); 13C NMR δ (ppm) 21.9, 33.8, 34.4 (CH2),
56.7 (CH-N), 82.3 (CH-O), 160.3 (CO); ESIMS m/z 150 (M +
Na)+. Anal. Calcd for C6H9NO2: C, 56.68; H, 7.13; N, 11.02.
Found: C, 56.50; H, 7.22; N, 10.91. GC conditions: 170 °C, 10
min; 2 °C/min until 200 °C. tR (min): (3aS,6aR)-4a , 14.8; (3aR,-
6aS)-4a , 15.1.
Ben zyl (1S,2S)-N-[(2-H yd r oxycycloh exyl)m et h yl]ca r -
20
ba m a te, 6b: yield 90%, colorless oil; [R]D +6.4 (c 2.9, CHCl3);
1
(3a R,7a S)-P er h yd r oben zo[d ]oxa zol-2-on e, 4b: yield 94%,
ee 93%; IR ν (cm-1) 1715; H NMR δ (ppm) 1.15-1.85 (m, 9H),
20
white solid; mp 92-93 °C; [R]D -28.8 (c 1.4, CHCl3); ee 93%;
2.92 (m, 1H, CHH-N), 3.31 (m, 1H, CHH-N), 2.3-3.5 (bs, 1H,
OH), 3.88 (m, 1H, CH-O), 5.09 (s, 2H, CH2-O), 5.28 (bs, 1H,
NH), 7.33 (m, 5H, arom); 13C NMR δ (ppm) 20.0, 24.2, 25.1, 32.3
(CH2), 42.1 (CH), 43.1 (CH2-N), 65.7 (CH-O), 66.8 (CH2-O),
127.9, 128.0, 128.4 (CHarom), 136.2 (Carom), 157.6 (CO); ESIMS
m/z 286 (M + Na)+. Anal. Calcd for C15H21NO3: C, 68.42; H,
8.04; N, 5.32. Found: C, 68.20; H, 8.18; N, 5.16.
IR ν (cm-1) 1757; 1H NMR δ (ppm) 1.2-1.35 (m, 1H), 1.35-1.65
(m, 4H), 1.65-1.85 (m, 2H), 1.9-2.0 (m, 1H), 3.72 (m, 1H, CH-
N), 4.55 (m, 1H, CH-O), 6.40 (bs, 1H, NH); 13C NMR δ (ppm)
19.3, 19.6, 26.5, 28.4 (CH2), 51.5 (CH-N), 75.8 (CH-O), 160.8
(CO); ESIMS m/z 164 (M + Na)+. Anal. Calcd for C7H11NO2: C,
59.56; H, 7.85; N, 9.92. Found: C, 59.24; H, 8.01; N, 9.80. GC
conditions: 170 °C, 10 min; 2 °C/min until 200 °C. tR (min):
(3aS,7aR)-4b, 18.2; (3aR,7aS)-4b, 18.5.
Ack n ow led gm en t. Financial support of this work
by the Spanish Ministerio de Ciencia y Tecnolog´ıa
(Project PPQ-2001-2683) and by Principado de Asturias
(Project GE-EXP01-03) is gratefully acknowledged.
J .R.D. thanks the Spanish Ministerio de Educacio´n,
Cultura y Deporte for a predoctoral fellowship. We also
thank Mr. I. Lavandera for the potentiometric measure-
ments.
Hyd r olyses of th e Oxa zolid in on es 4. The corresponding
compound 4 (0.5 mmol) was added to a solution of LiOH (100
mg) in 2.5 mL of an 8:1 water/methanol mixture. After the
mixture was refluxed for 2 h, solvents were evaporated, and the
residue was solved in Et2O, filtered, and concentrated again. To
the oil obtained were added Na2CO3 (0.6 mmol), water (1 mL),
and benzyl chloroformate (1 mmol) at 0 °C. The reaction mixture
was allowed to reach room temperature and shaken overnight.
After extraction with CH2Cl2, the product was isolated by column
chromatography (eluent 2:1 hexane/AcOEt).
Ben zyl (1R,2S)-N-(2-Hyd r oxycyclop en tyl)ca r ba m a te, 5a :
yield 76%, white solid; mp 55-56 °C; [R]D20 +35.0 (c 1.3, EtOH);
ee 97%; IR ν (cm-1) 1717; 1H NMR δ (ppm) 1.45-1.7 (m, 3H),
1.7-2.0 (m, 3H), 2.17 (bs, 1H, OH), 3.86 (m, 1H, CH-N), 4.15
Su p p or t in g In for m a t ion Ava ila b le: 1H and 13C NMR
spectra of 2a ,b, 3a ,b, 4a ,b, 5a ,b, and 6a ,b. This material is
available free of charge via the Internet at http://pubs.acs.org.
J O0257288
J . Org. Chem, Vol. 67, No. 19, 2002 6819