CAL-B-catalyzed alkoxycarbonylation of A-ring stereoisomeric synthons of 1α,25-dihydroxyvitamin D3 and 1α,25-dihydroxy-19-nor-previtamin D3: A comparative study. First regioselective chemoenzymatic synthesis of 19-nor-A-ring carbonates

Article abstract of DOI:10.1021/jo010017f

A comparative study of alkoxycarbonylation processes of both 19-nor-A-ring and A-ring stereoisomers of 1α,25-dihydroxyvitamin D₃ analogues catalyzed by Candida antarctica lipase B (CAL-B) has been described. The presence of the methyl group in the A-ring at C-2, as in 3-6, has a determining role in the regioselectivity of the biocatalysis, mainly allowing the hydroxyl group at C-5 position to react. For the 19-nor-A-ring stereoisomers 7-10, which lack the C-2 methyl group, the configurations at C-3 and C-5 have a high influence in the selectivity exhibited by CAL-B. Thus, each couple of enantiomers showed opposing regioselectivities depending on the C-3 configuration. When C-3 possesses an (S)-configuration, enzymatic alkoxycarbonylations took place at the C-5-(R) or C-5-(S) hydroxyl groups. However, if the chiral centers at C-3 are (R), CAL-B alkoxycarbonylated the C-3-(R) hydroxyl group independently of the configuration at C-5. The corresponding carbonates are useful A-ring precursors of 1α,25-dihydroxyvitamin D₃ analogues, selectively modified at the C-1 or C-3 positions. In addition, an improved synthesis of cis A-ring synthons 5 and 6 is described using a Mitsunobu methodology.

Full text of DOI:10.1021/jo010017f

J . Org. Chem. 2001, 66, 4227-4232
4227
CAL-B-Ca ta lyzed Alk oxyca r bon yla tion of A-Rin g Ster eoisom er ic
Syn th on s of 1r,25-Dih yd r oxyvita m in D3 a n d
1r,25-Dih yd r oxy-19-n or -p r evita m in D3: A Com p a r a tive Stu d y.
F ir st Regioselective Ch em oen zym a tic Syn th esis of 19-n or -A-Rin g
Ca r bon a tes
Mo´nica D´ıaz, Vicente Gotor-Ferna´ndez, Miguel Ferrero, Susana Ferna´ndez, and
Vicente Gotor*
Departamento de Quı´mica Orga´nica e Inorga´nica, Facultad de Qu´ımica, Universidad de Oviedo,
33071-Oviedo, Spain
VGS@sauron.quimica.uniovi.es
Received J anuary 5, 2001
A comparative study of alkoxycarbonylation processes of both 19-nor-A-ring and A-ring stereoisomers
of 1R,25-dihydroxyvitamin D3 analogues catalyzed by Candida antarctica lipase B (CAL-B) has
been described. The presence of the methyl group in the A-ring at C-2, as in 3-6, has a determining
role in the regioselectivity of the biocatalysis, mainly allowing the hydroxyl group at C-5 position
to react. For the 19-nor-A-ring stereoisomers 7-10, which lack the C-2 methyl group, the
configurations at C-3 and C-5 have a high influence in the selectivity exhibited by CAL-B. Thus,
each couple of enantiomers showed opposing regioselectivities depending on the C-3 configuration.
When C-3 possesses an (S)-configuration, enzymatic alkoxycarbonylations took place at the C-5-
(R) or C-5-(S) hydroxyl groups. However, if the chiral centers at C-3 are (R), CAL-B alkoxycarbo-
nylated the C-3-(R) hydroxyl group independently of the configuration at C-5. The corresponding
carbonates are useful A-ring precursors of 1R,25-dihydroxyvitamin D3 analogues, selectively modified
at the C-1 or C-3 positions. In addition, an improved synthesis of cis A-ring synthons 5 and 6 is
described using a Mitsunobu methodology.
Ch a r t 1
In tr od u ction
To perform regio- and stereoselective transformations,
and because of their simple feasibility and high efficiency,
enzyme-catalyzed reactions have become standard pro-
cedures in organic synthesis.1 In general, these catalysts
are inexpensive and in many cases able to adapt to a wide
range of substrate structures. Moreover, biocatalysts are
ecologically beneficial natural catalysts. Previously, we
reported the regioselective enzymatic acylation2 and
alkoxycarbonylation3 reactions of 1R,25-dihydroxyvita-
min D3 A-ring precursors 3-6 (Chart 1). The hormonal
active form (2, Chart 1) of vitamin D3 (1) has, apart from
its normal role as a calcium regulator, a wide range of
activities such as modulation of cell proliferation and
differentiation.4 Most of the analogues5 are altered in the
side chain, although modifications in the A-ring, less
accessible synthetically, provide vitamin D derivatives
with an unique biological profile.6 The A-ring synthon
(1) (a) Carrea, G.; Riva, S. Angew. Chem., Int. Ed. 2000, 39, 2226-
2254. (b) Bornscheuer, U. T.; Kazlauskas, R. J . Hydrolases in Organic
Synthesis: Regio- and Stereoselective Biotransformations; Wiley-
VCH: Weinheim, 1999. (c) Faber, K. Biotransformations in Organic
Chemistry, 4th ed.; Springer-Verlag: Berlin, 2000.
possesses two hydroxyl groups of similar reactivity, and
as a result it is very difficult to discern between these
(2) Ferna´ndez, S.; Ferrero, M.; Gotor, V.; Okamura, W. H. J . Org.
Chem. 1995, 60, 6057-6061.
(6) (a) Tsugawa, N.; Nakagawa, K.; Kurobe, M.; Ohno, Y.; Kubodera,
N.; Ozono, K.; Okano, T. Biol. Pharm. Bull. 2000, 23, 66-71. (b)
Sicinski, R. R.; Prahl, J . M.; Smith, C. M.; DeLuca, H. F. J . Med. Chem.
1998, 41, 4662-4674. (c) Posner, G. H.; Lee, J . K.; White, M. C.;
Hutchings, R. H.; Dai, H.; Kachinski, J . L.; Dolan, P.; Kensler, T. W.
J . Org. Chem. 1997, 62, 3299-3314. (d) Daniel, D.; Middleton, R.;
Henry, H. L.; Okamura, W. H. J . Org. Chem. 1996, 61, 5617-5625.
(e) Posner, G. H.; Cho, C.-G.; Anjeh, T. E. N.; J ohnson, N.; Horst, R.
L.; Kobayashi, T.; Okano, T.; Tsugawa, N. J . Org. Chem. 1995, 60,
4617-4628.
(3) (a) Gotor-Ferna´ndez, V.; Ferrero, M.; Ferna´ndez, S.; Gotor, V.
J . Org. Chem. 1999, 64, 7504-7510. (b) Ferrero, M.; Ferna´ndez, S.;
Gotor, V. J . Org. Chem. 1997, 62, 4358-4363.
(4) (a) Vitamin D; Feldman, D.; Glorieux, F. H.; Pike, J . W., Eds.;
Academic Press: New York, 1997. (b) Ettinger, R. A.; DeLuca, H. F.
Adv. Drug Res. 1996, 28, 269-312. (c) Bouillon, R.; Okamura, W. H.;
Norman, A. W. Endocrine Rev. 1995, 16, 200-257
(5) (a) Zhu, G.-D.; Okamura, W. H. Chem. Rev. 1995, 95, 1877-
1952. (b) Dai, H.; Posner, G. H. Synthesis 1994, 1383-1398.
10.1021/jo010017f CCC: $20.00 © 2001 American Chemical Society
Published on Web 05/17/2001

4228 J . Org. Chem., Vol. 66, No. 12, 2001
D´ıaz et al.
Sch em e 1
thons to prepare 6-s-cis-locked analogues of 1R,25-dihy-
droxyvitamin D3 has been previously described.10 To
compare both enzymatic alkoxycarbonylation processes,
similar reaction conditions were used to those previously
described for 3-6. All reactions were carefully monitored
by GC to determine the conversion. Ratio of C-3, C-5, or
C-3,5 derivatives were calculated by 1H NMR since these
alkoxycarbonylation products were too close in GC chro-
matograms. Thus, reaction of A-ring synthon 7 (Scheme
1) with 10 equiv of acetone O-[(vinyloxy)carbonyl]oxime
(23a ) in toluene at 30 °C in the presence of CAL-B gave,
after 3 h and 98% conversion, moderate selectivity toward
C-5 (compound 12a ) in addition to C-3 (11a ) and a small
amount of C-3,5 (13a ) derivatives (entry 1, Table 1). This
result contrasts with that reported for compound 3, in
which total regioselectivity toward C-5 position was
achieved.3b This indicates that the presence of the C-2
methyl group has an important influence in the enzy-
matic catalysis. To increase the selectivity, and taking
into account the high reaction rate, fewer equivalents of
23a were added. This change did not drastically increase
the ratio of 12a (entry 2, Table 1). The shorter reaction
time, compared with entry 1, is probably due to the
inhibition of the enzyme when large amount of alkoxy-
carbonylation agent were added to the reaction mixture.
A decrease in temperature did not lead to an increase of
selectivity (entry 3, Table 1). When the substrate was
19-nor-A-ring 8, C-5 carbonate 15a was obtained as the
major product, both at 15 or 30 °C (entries 4 and 5, Table
1), although the regioselectivity was similar to that
shown by its enantiomer 7. The selectivity of the process
did not experience an improvement when the biocatalysis
was carried out with stereoisomers 9 and 10 (entries 6-9,
Table 1). CAL-B mainly catalyzed the formation of the
corresponding C-3,5 carbonates 19a and 22a .
In view of these unsuccessful results and taking into
account our aim to prepare regioselective modified 19-
nor-A-ring synthons, we decided to study the enzymatic
alkoxycarbonylation process with acetone O-(phenoxy-
carbonyl)oxime (23b). The latter carbonate has shown
better regioselectivities than acetone O-[(vinyloxy)car-
bonyl]oxime (23a ) in CAL-B-catalyzed alkoxycarbonyla-
tion in nucleosides.11 Besides their intrinsic value, the
A-ring phenoxycarbonates generated are excellent inter-
mediates for consecutive modifications since phenol is,
like acetaldehyde, a good leaving group. Table 2 sum-
marizes the results obtained for the alkoxycarbonylation
of isomers 7-10 with CAL-B and carbonate 23b at 30
°C in toluene. This lipase catalyzes carbonate formation
on the C-5 hydroxyl group in compound 7 with excellent
regioselectivity (entry 1, Table 2), isolating derivative
12b. A parallel experiment was carried out with its
stereoisomer, 8. The high selectivity of the enzyme
toward the C-3 position (isolating 14b) is noteworthy and
is the very opposite of enantiomer 7 (entry 2, Table 2).
When the reaction was carried out on cis-diol 9, excellent
selectivity toward the C-5 hydroxyl was achieved. Since
this compound is less reactive than that previously
mentioned, the reaction took place with 4 equiv of 23b,
yielding 97% conversion in 24 h (entry 3, Table 2). To
get total selectivity, 2 equiv of alkoxycarbonylating agent
two groups from a chemical point of view. An important
and synthetically relevant transformation in lipase-
mediated reactions in organic solvents is the selective
modification of polyfunctionalized compounds, such as
carbohydrates,7 steroids,8 and nucleosides.9
Candida antarctica lipase B (CAL-B) catalyzes selec-
tively the alkoxycarbonylation of the C-5 hydroxyl group
of the four stereoisomeric vitamin D A-ring precursors
3, 4, 5, and 6.3 It is possible to obtain the monocarbonate
derivatives at C-5 with excellent regioselectivity using
acetone O-[(vinyloxy)carbonyl]oxime (23a ) (Scheme 1) as
the alkoxycarbonylation reagent in toluene. Here we
report a systematic study of the influence of the methyl
group at C-2 in the selectivity of the process. The study
aims to go into the selectivity of CAL-B with these
substrates in depth, and to provide easy access to
selectively modified 19-nor-A-ring synthons. Different
alkoxycarbonylation agents are investigated. In addition,
we describe an alternative approach to synthesize the cis-
diol isomers 5 and 6, this being more efficient on the basis
of its fewer steps an high overall yields.
Resu lts a n d Discu ssion
Alk oxyca r bon yla tion of 19-n or -A-Rin g Syn th on s
7-10. The synthesis of these A-ring precursors as syn-
(7) Drueckhammer, D. G.; Hennen, W. J .; Pederson, R. L.; Barbas,
C. F., III.; Gautheron, C. M.; Krach, T.; Wong, C.-H. Synthesis 1991,
499-525. (b) Gijsen, H. J . M.; Qiao, L.; Fitz, W.; Wong, C.-H. Chem.
Rev. 1996, 96, 443-473.
(8) Ferrero, M.; Gotor, V. In Stereoselective Biocatalysis; Patel, R.
N., Ed.; Marcel Dekker: New York, 1999; Chapter 20, pp 579-631.
(9) Ferrero, M.; Gotor, V. Chem. Rev. 2000, 100, 4319-4348.
(10) (a) D´ıaz, M.; Ferrero, M.; Ferna´ndez, S.; Gotor, V. Tetrahedron
Lett. 2000, 41, 775-779. (b) D´ıaz, M.; Ferrero, M.; Ferna´ndez, S.; Gotor,
V. J . Org. Chem. 2000, 65, 5647-5652.
(11) Garc´ıa-Alles, L. F.; Gotor, V. J . Mol. Catal. B: Enzymatic 1999,
6, 407-410.

Synthons of 1R,25-Dihydroxyvitamin D3
J . Org. Chem., Vol. 66, No. 12, 2001 4229
Ta ble 1. En zym a tic Alk oxyca r bon yla tion Ca ta lyzed by CAL-B of 19-n or -A-Rin g Syn th on s 7-10 w ith Ca r bon a te 23a
entry
substrate
T (°C)
23a (equiv)a
t (h)
conv (%)b
C-3 (%)c,d
C-5 (%)c,d
C-3,5 (%)c,d
1
2
3
4
5
6
7
8
9
7
7
7
8
8
9
9
10
10
30
30
15
30
15
30
30
15
30
10
3
3
1
20
1.5
3
26
15
72
36
98
99
98
98
96
97
92
90
95
30
20
30
32
32
43
25
24
43
60
66
41
60
64
30
31
4
8
13
27
6
4e
2
2
4
5
5
24
36
62
47
2
5
a
Equivalents of 23a were chosen according to their relative reactivity compared to A-ring synthons 3-6 which has already been reported.
Calculated by GC, using Method A. c Ratio of regioselectivity at position C-3, C-5, or C-3,5, calculated by 1H NMR. Some of these
b
d
percentages contains, in addition to the vinyl derivative, the corresponding oxime. e 3 + 1.
Ta ble 2. En zym a tic Alk oxyca r bon yla tion Ca ta lyzed by
CAL-B a t 30 °C of 19-n or -A-Rin g Syn th on s 7-10 w ith
Ca r bon a te 23b
Sch em e 2
entry substrate 23b (equiv) t (h) conv (%)a C-3 (%)b C-5 (%)b
1
2
3
4
5
7
8
9
9
10
2
2
4
2
3
14
18
24
26
20
100
100
97
100
98
10
80
5
4
98
90
20
92
96
a
b
Calculated by GC, using Method A. Ratio of regioselectivity
at position C-3 or C-5, calculated by 1H NMR.
23b was used. Thus after 26 h, 100% conversion was
achieved with a selectivity of 96% for 18b (entry 4, Table
2). Opposite regioselectivity was obtained with isomer 10,
forming compound 20b exclusively (entry 5, Table 2).
From the experimental data reported in Table 2, we can
conclude that if the configuration of C-3 is (S), as in 7
and 9, CAL-B-catalyzed alkoxycarbonylation in the C-5
position, independent of its configuration. On the other
hand, when C-3 possesses an (R)-configuration, as in 8
and 10, the enzyme prefers this center to perform the
catalysis. It is worth noting that regioselectivity is
opposite for each couple of enantiomers, that is, 7 vs 8
and 9 vs 10. Results in Table 1 and Table 2 reveal that
the nature of the carbonate employed have a key influ-
ence on the regioselectivity of the biocatalytic alkoxycar-
bonylation reaction. While the acetone O-[(vinyloxy)-
carbonyl]oxime gave poor selectivities (Table 1), acetone
O-(phenoxycarbonyl)oxime showed from high to excellent
regioselectivities for substrates 7-10.
Im p r oved Syn th esis of A-Rin g Cis Ster eoisom er s
5 a n d 6. The synthesis of the stereoisomeric diols 5 and
6 has been previously described2 by ourselves from diols
3 and 412 through the oxidation of the C-3 allylic alcohol
using Dess-Martin reagent, and subsequent reduction
of the resulting ketones in a 3:1 cis to trans selectivity.
Recently, an alternative procedure to protected diol 5 has
also been reported13 but with the problem of the very poor
yield with which the ozonolysis step takes place on the
terminal alkene in a (R)-carvone derivative. Because of
these drawbacks, here we propose an alternative prepa-
ration to obtain single isomers 5 and 6 (Scheme 2). Thus,
starting from (R)-carvone (24), alcohol 25 was obtained
in five steps and 46% overall yield. Inversion of the later
alcohol under Mitsunobu conditions using p-nitrobenzoic
acid afforded p-nitrobenzoate ester 26 with total inver-
sion of the configuration and high yield.12a Acetic acid
instead of p-nitrobenzoic acid gave lower yields, since
substantial amounts of starting alcohol 25 were recov-
ered, even when longer reaction times, higher tempera-
tures, and more equivalents of reactants were used.
Simultaneous deprotection of both ester groups in deriva-
tive 26 was carried out with NaOMe in MeOH to obtain
cis-diol 5 with excellent yield. Similarly, cis-diol 6 was
obtained from (S)-carvone.
Alk oxyca r bon yla tion of A-Rin g Syn th on s 3-6. As
previously mentioned, the CAL-B-catalyzed enzymatic
alkoxycarbonylation of stereoisomeric diols 3-6, which
possess the C-2 methyl group in their structure, using
acetone O-[(vinyloxy)carbonyl]oxime (23a ), takes place
with excellent regioselectivity (>97%) toward the C-5
position for compounds 3-5, whereas cis-isomer 6 shows
moderate regioselectivity (76%) to the same position, in
addition to a considerable percentage (22%) of C-3,5
divinyl derivative.3 Taking into account the excellent
regioselectivity obtained when carbonate 23b is used as
the alkoxycarbonylating agent in 19-nor-A-ring sub-
strates 7-10, as well as the different behavior between
enantiomers, we set out to study the effect of carbonate
23b on diols 3-6 with two goals in mind. The first was
to increase the regioselectivity of the process for isomer
6. The second goal was to check if the enzyme keeps its
structural preferences by changing the alkoxycarbony-
(12) Compounds 3 and 4 have been synthesized by Okamura from
(S)- and (R)-carvone, respectively: (a) Muralidharan, K. R.; de Lera,
A. R.; Issaeff, S. D.; Norman, A. W.; Okamura. W. H. J . Org. Chem.
1993, 58, 1895-1899. (b) Okamura, W. H.; Aurrecoechea, J . M.; Gibbs,
R. A.; Norman, A. W. J . Org. Chem. 1989, 54, 4072-4083. (c)
Aurrecoechea, J . M.; Okamura, W. H. Tetrahedron Lett. 1987, 28,
4947-4950.
(13) Srikrishna, A.; Gharpure, S. J .; Kumar, P. P. Tetrahedron Lett.
2000, 41, 3177-3180.

4230 J . Org. Chem., Vol. 66, No. 12, 2001
D´ıaz et al.
Sch em e 3
view because both compounds, 32a ,b or 33a ,b, are
appropriate synthons for use as precursors to introduce
additional functionalities, taking into account that the
combined isolated yields are high.
From the results in Table 2 and Table 3, it seems that
the methyl group in the C-2 position is crucial to
accommodate substrates 3-6, independent of their ster-
eochemistry, inside the enzyme active site in a way that
mainly allows the available hydroxyl group to react at
C-5 position.
Su m m a r y
Candida antarctica lipase B (CAL-B) has catalyzed
with excellent selectivity the alkoxycarbonylation process
of 19-nor-A-ring stereoisomers 7-10 of 1R,25-dihydroxy-
19-nor-previtamin D3 with acetone O-(phenoxycarbonyl)-
oxime (23b). The opposite regioselectivity shown by each
couple of enantiomers (7 vs 8 and 9 vs 10) is noteworthy.
Thus, when C-3 possesses an (S)-configuration (as 7 or
9), CAL-B-catalyzed alkoxycarbonylation in the C-5 posi-
tion, independent of its own configuration. Meanwhile,
if C-3 has an (R)-configuration (as 8 or 10), the enzyme
performed the reaction at this center. For the A-ring
stereoisomers of 1R,25-dihydroxyvitamin D3 3-6, which
possess the C-2 methyl group, the enzymatic process took
place toward the C-5 position independent of the stereo-
chemistry at the chiral centers. The methyl group in the
C-2 position is crucial in the accommodation of these
substrates inside the enzyme active site. Besides the
intrinsic importance of these A-ring carbonates, this
group facilitates the introduction of different function-
alities. Selective modification at the C-1 or C-3 positions
of 6-s-cis locked analogues (previtamin forms) or 6-s-trans
derivatives of 1R,25-dihydroxyvitamin D3, could be ob-
tained. In addition, an improved synthesis of cis-diols 5
and 6 was described using a Mitsunobu procedure.
Ta ble 3. En zym a tic Alk oxyca r bon yla tion Ca ta lyzed by
CAL-B of A-Rin g Syn th on s 3-6 w ith Ca r bon a te 23b
yield C-5 (%)b
T
23b
t
conv
entry substrate (°C) (equiv) (h) (%)a Ph Me2CdN
1
2
3
4
5
6
7
9
3
4
5
5
5
6
6
6
30
30
30
45
45
30
45
45
3
3
3
3
6
3
3
6
24 100
90
87
56
56
55
6
2
96
32
24
96
80
24
100
89
88
26
20
28
16
61
38
87
41c
Exp er im en ta l Section 14
92c 17
64c 10
Gen er a l. Candida antarctica lipase B (CAL-B, 7300 PLU/
g) was a gift from Novo Nordisk Co. Reagents were purchased
from Aldrich or Fluka. Solvents were distilled over an ap-
propriate desiccant under nitrogen. Syntheses of A-ring 3-62,12
and 19-nor-A-ring 7-1010 precursors were previously reported.
Carbonates 30, 32b, and 33b were described.3 Oxime carbon-
ates 23a ,b were synthesized as has been described.15 Dowex
50WX4-400 ion-exchange resin (200-400 mesh) was washed
with H2O prior to use. Gas chromatography was carried out
with flame ionization detection (FID) and a HP-1 capillary
column (25 m × 0.2 mm × 0.33 µm) coated with methylsilicone
gum, with nitrogen as carrier gas and following two different
methods. Meth od A: injector and detector temperatures set
at 300 °C, column initial temperature 130 °C (3 min), rate 7
°C/min until 200 °C (15 min) and then 15 °C/min, column final
temperature 270 °C; acetanilide (as internal standard) ap-
peared at 6.8 min; 7 and 8 at 5.9 min; 9 and 10 at 5.8 min;
11a and 14a at 10.4 min; 12a and 15a at 10.3 min; 13a and
a
Calculated by GC, using Method B. b Isolated yields after flash
chromatography. c Di-derivatives such as C-3,5 dioxime and C-3,5
phenyl-oxime carbonates were formed as minor compounds.
lating agent. We found that the use of acetone O-
(phenoxycarbonyl)oxime for the alkoxycarbonylation of
trans-diols 3 and 4 did not affect the regioselectivity of
the reaction, and we isolated exclusively C-5 carbonates
30 and 31 (Scheme 3), respectively, with high yields
(entries 1 and 2, Table 3). When the same process was
carried out with isomer 5, total regioselectivity toward
the C-5 position was obtained although two products are
formed, C-5 phenyl carbonate 32a , and C-5 oxime car-
bonate 32b (entry 3, Table 3). Considering the hypothesis
that longer reaction times favor the formation of 32b,
and in order to prepare just 32a , higher temperature and
more equivalents of carbonate 23b were used. No differ-
ences were observed with these changes (entries 4 and
5, Table 3). A similar pattern of results was observed with
isomer 6. In this case, C-5 oxime carbonate 33b was the
major product and, in addition to the C-5 phenyl carbon-
ate 33a , di-derivatives such as C-3,5 dioxime and C-3,5
phenyl-oxime were formed as minor compounds. Al-
though two different C-5 derivatives are obtained, this
fact is not an inconvenience from the synthetic point of
(14) Structures of the products are numbered as follows:
(15) Ferna´ndez, S.; Mene´ndez, E.; Gotor, V. Synthesis 1991, 713-
716.

Synthons of 1R,25-Dihydroxyvitamin D3
J . Org. Chem., Vol. 66, No. 12, 2001 4231
16a at 14.0 min; 17a and 20a at 10.2 min; 18a and 21a at
10.3 min; 19a and 22a at 14.3 min. Conversion of the reaction
for phenoxycarbonyl derivatives was calculated by disappear-
ance of the starting material with respect to internal standard.
Meth od B: injector and detector temperatures set at 250 °C
and 275 °C, respectively, column initial temperature 150 °C
(3 min), rate 18 °C/min, column final temperature 260 °C (20
min); naphthalene (as internal standard) appeared at 3.3 min;
3 and 4 at 4.7 min; 5 and 6 at 4.6 min; 30 and 31 at 11.1 min;
32a and 33a at 7.5 min; 32b and 33b at 7.6 min.
H3), 5.55 (m, 1H, H5), 6.22 (m, 1H, H2), and 7.05 (m, 2H,
H10+H13); MS (ESI+, m/z): 279 [M + H]+ and 301 [M + Na]+.
(3S,5S)- an d (3R,5R)-1-Eth yn yl-5-h ydr oxy-3-[(vin yloxy)-
car bon yloxy]cycloh ex-1-en e (17a an d 20a). 1H NMR (CDCl3,
200 MHz): δ 1.90-2.80 (several m, 4H, H4+H6), 2.92 (s, 1H,
3
2
H8), 4.15 (m, 1H, H5), 4.53 (dd, 1H, H11-cis, J HH ) 6.2, J HH
3
2
) 2.1 Hz), 4.82 (dd, 1H, H11-trans, J HH ) 13.9, J HH ) 2.1
Hz), 5.33 (m, 1H, H3), 6.24 (m, 1H, H2), and 6.98 (dd, 1H,
H10, J HH ) 13.9, J HH ) 6.2 Hz); MS (ESI+, m/z): 231 [M +
3
3
Na]+.
(3S,5S)-1-E t h yn yl-3,5-d ih yd r oxy-2-m et h ylcycloh ex-1-
en e (5). A solution of MeONa in MeOH, prepared in situ by
addition of Na (67 mg, 2.93 mmol) to MeOH (2.5 mL), was
added dropwise to a solution of 26 (430 mg, 1.25 mmol) in
MeOH (14 mL) at 0 °C. The reaction was stirred at this
temperature for 2.5 h and then acidified with Dowex 50WX4-
400 ion-exchange resin (200-400 mesh). After removal of the
resin by filtration, the solution was evaporated, and the
residue was purified by flash chromatography (50% EtOAc/
hexane) to afford 183 mg (96%) of diol 5 as a white solid: 1H
NMR (CDCl3, 300 MHz): δ 1.55 (br s, 1H, OH), 1.86 (ddd, 1H,
H4, J HH ) 14.2, J HH ) 5.0, J HH ) 2.1 Hz), 2.06 (s, 3H, H9),
2.13-2.24 (m, 1H, H4), 2.25-2.52 (m, 2H, H6), 3.02 (br s, 1H,
OH), 3.10 (s, 1H, H8), 4.04 (m, 1H, H5), and 4.28 (m, 1H, H3);
HRMS (EI, m/z): Calcd for C9H12O2 (M+): 152.0837. Found:
152.0846.
(3S,5S)- a n d (3R,5R)-1-Eth yn yl-5-h yd r oxy-3-(p h en oxy-
ca r b on yloxy)cycloh ex-1-en e (17b a n d 20b ). 1H NMR
(CDCl3, 200 MHz): δ 1.93-2.10 (m, 2H, H4), 2.28-2.57 (m,
2H, H6), 3.00 (s, 1H, H8), 4.09 (m, 1H, H5), 5.41 (m, 1H, H3),
6.27 (m, 1H, H2), and 7.17-7.45 (m, 5H, ArH); MS (ESI+,
m/z): 281 [M + Na]+.
(3S,5S)- an d (3R,5R)-1-Eth yn yl-3-h ydr oxy-5-[(vin yloxy)-
car bon yloxy]cycloh ex-1-en e (18a an d 21a). 1H NMR (CDCl3,
200 MHz): δ 1.90-2.80 (several m, 4H, H4+H6), 2.82 (s, 1H,
3
2
H8), 4.55 (m, 1H, H3), 4.53 (dd, 1H, H11-cis, J HH ) 6.1, J HH
3
2
) 2.0 Hz), 4.82 (dd, 1H, H11-trans, J HH ) 13.8, J HH ) 2.0
2
3
3
Hz), 5.13 (m, 1H, H5), 6.24 (m, 1H, H2), and 6.98 (dd, 1H,
H10, J HH ) 13.8, J HH ) 6.1 Hz); MS (ESI+, m/z): 231 [M +
3
3
Na]+.
(3S,5S)- a n d (3R,5R)-1-Eth yn yl-3-h yd r oxy-5-(p h en oxy-
ca r b on yloxy)cycloh ex-1-en e (18b a n d 21b ). 1H NMR
(CDCl3, 200 MHz): δ 1.95-2.21 (m, 2H, H4), 2.57 (m, 2H, H6),
2.96 (s, 1H, H8), 4.37 (m, 1H, H3), 5.15 (m, 1H, H5), 6.32 (m,
1H, H2), and 7.16-7.42 (m, 5H, ArH); MS (ESI+, m/z): 281
[M + Na]+.
(3R,5R)-1-Eth yn yl-3,5-d ih yd r oxy-2-m eth ylcycloh ex-1-
en e (6). The same procedure as that described for 5 yielded 6
(89%). Spectral data are identical to that of 5 given above.
En zym a tic Alk oxyca r bon yla tion of 7-10. Syn th esis of
Ca r bon a tes 11-22. In a typical procedure, CAL-B (45 mg)
was added to a solution of diol 7-10 (9 mg, 0.066 mmol) and
carbonate 23a ,b in toluene (2.5 mL, acetanilide is present as
internal standard in 0.013 M) under nitrogen. Equivalents of
alkoxycarbonylation agent, temperature, and reaction time are
given in Table 1 and Table 2. The suspension was shaken, and
the progress of the reaction was followed by GC analysis. Close
to 100% conversion the mixture was filtered, and the solvent
(3S,5S)- a n d (3R,5R)-1-Eth yn yl-3,5-d i[(vin yloxy)ca r bo-
n yloxy]cycloh ex-1-en e (19a a n d 22a ). 1H NMR (CDCl3, 200
MHz): δ 1.90-2.80 (several m, 4H, H4+H6), 2.82 (s, 1H, H8),
4.53 (m, 2H, H11+H14), 4.82 (m, 2H, H11+H14), 4.95 (m, 1H,
H3), 5.43 (m, 1H, H5), 6.25 (m, 1H, H2), and 6.99 (m, 2H,
H10+H13); MS (ESI+, m/z): 279 [M + H]+ and 301 [M + Na]+.
(3S,5S)-5-Acetoxy-1-eth yn yl-2-m eth yl-3-[(4-n itr oph en yl)-
ca r bon yloxy]cycloh ex-1-en e (26). To a stirred solution of
25 (300 mg, 1.54 mmol) in THF (21 mL) under nitrogen were
added 4-nitrobenzoic acid (516 mg, 3.09 mmol), PPh3 (810 mg,
3.09 mmol), and diethyl azodicarboxylate (0.48 mL, 3.09
mmol). The mixture was stirred for 1 h at room temperature
and then evaporated under reduced pressure to leave a residue
which was purified by flash chromatography (10% EtOAc/
hexane); oil, yield 472 mg (89%): 1H NMR (CDCl3, 300 MHz):
1
was removed under reduced pressure. After H NMR analysis,
the crude material was subjected to flash chromatography
(15% EtOAc/hexane) to give compounds 11-22.
(3S,5R)- an d (3R,5S)-1-Eth yn yl-5-h ydr oxy-3-[(vin yloxy)-
car bon yloxy]cycloh ex-1-en e (11a an d 14a). 1H NMR (CDCl3,
200 MHz): δ 1.90-2.80 (several m, 4H, H4+H6), 2.80 (s, 1H,
3
2
H8), 4.15 (m, 1H, H5), 4.55 (dd, 1H, H11-cis, J HH ) 6.4, J HH
3
2
2
) 2.1 Hz), 4.92 (dd, 1H, H11-trans, J HH ) 13.6, J HH ) 2.1
δ 1.95 (s, 3H, H9), 1.98 (s, 3H, H11), 2.12 (ddd, 1H, H4, J HH
3
3
2
Hz), 5.50 (m, 1H, H3), 6.22 (m, 1H, H2), and 7.05 (dd, 1H,
) 13.9, J HH ) 8.3, J HH ) 6.1 Hz), 2.31 (ddd, 1H, H4, J HH
)
H10, J HH ) 13.6, J HH ) 6.4 Hz); MS (ESI+, m/z): 209 [M +
3
2
3
3
13.5, J HH ) 5.7, J HH ) 3.1 Hz), 2.43 (m, 1H, H6), 2.58 (d,
H]+.
2
1H, H6, J HH ) 17.0 Hz), 3.21 (s, 1H, H8), 5.08 (m, 1H, H5),
3
(3S,5R)- a n d (3R,5S)-1-Eth yn yl-5-h yd r oxy-3-(p h en oxy-
ca r b on yloxy)cycloh ex-1-en e (11b a n d 14b ). 1H NMR
(CDCl3, 200 MHz): δ 1.90-2.26 (m, 3H, 2H4+H6), 2.63 (dd,
5.70 (apparent t, 1H, H3, J HH ) ∼5.6 Hz), 8.19 (d, 2H, H15,
3J HH ) 2.2 Hz), and 8.29 (d, 2H, H14, 3J HH ) 2.2 Hz); MS (ESI+,
m/z): 366 [M + Na]+.
2
1H, H6, J HH ) 17.4, J HH ) 5.2 Hz), 2.99 (s, 1H, H8), 4.25 (m,
(3R,5R)-5-Acetoxy-1-eth yn yl-2-m eth yl-3-[(4-n itr op h en -
yl)ca r bon yloxy]cycloh ex-1-en e (29). The same procedure
as that described for 26 yielded 29 (87%). Spectral data are
identical to that of 26 given above.
1H, H5), 5.44 (m, 1H, H3), 6.30 (m, 1H, H2), and 7.21-7.41
(m, 5H, ArH); MS (ESI+, m/z): 281 [M + Na]+.
(3S,5R)- an d (3R,5S)-1-Eth yn yl-3-h ydr oxy-5-[(vin yloxy)-
car bon yloxy]cycloh ex-1-en e (12a an d 15a). 1H NMR (CDCl3,
200 MHz): δ 1.90-2.80 (several m, 4H, H4+H6), 2.80 (s, 1H,
En zym a tic Alk oxyca r bon yla tion of 3-6. Syn th esis of
Ca r bon a tes 30-33. In a typical procedure, CAL-B (89 mg)
was added to a solution of diol 3-6 (20 mg, 0.13 mmol), and
carbonate 23b in toluene (5 mL, naphthalene is present as
internal standard in 0.066 M) under nitrogen. Equivalents of
23b, temperature, and reaction time are given in Table 3. The
suspension was shaken and the progress of the reaction was
followed by GC analysis. After removal of the enzyme by
filtration, evaporation of the solvent, and 1H NMR analysis,
the residual mixture was purified by flash chromatography
(gradient eluent 10-50% EtOAc/hexane) to give compounds
30-33.
3
2
H8), 4.45 (m, 1H, H3), 4.55 (dd, 1H, H11-cis, J HH ) 6.3, J HH
3
2
) 1.9 Hz), 4.92 (dd, 1H, H11-trans, J HH ) 13.6, J HH ) 1.9
Hz), 5.21 (m, 1H, H5), 6.24 (m, 1H, H2), and 7.05 (dd, 1H,
H10, J HH ) 13.6, J HH ) 6.3 Hz); MS (ESI+, m/z): 209 [M +
3
3
H]+.
(3S,5R)- a n d (3R,5S)-1-Eth yn yl-3-h yd r oxy-5-(p h en oxy-
ca r b on yloxy)cycloh ex-1-en e (12b a n d 15b ). 1H NMR
(CDCl3, 200 MHz): δ 2.02 (m, 1H, H4), 2.22 (m, 1H, H4), 2.42
(ddd, 1H, H6, 2J HH ) 17.9, J HH ) 5.9, J HH ) 1.8 Hz), 2.71 (ddd,
2
1H, H6, J HH ) 17.9, J HH ) 5.1, J HH ) 2.3 Hz), 2.94 (s, 1H,
H8), 4.54 (m, 1H, H3), 5.19 (m, 1H, H5), 6.25 (m, 1H, H2),
and 7.21-7.41 (m, 5H, ArH); MS (ESI+, m/z): 281 [M + Na]+.
(3S,5R)- a n d (3R,5S)-1-Eth yn yl-3,5-d i[(vin yloxy)ca r bo-
n yloxy]cycloh ex-1-en e (13a a n d 16a ). 1H NMR (CDCl3, 200
MHz): δ 1.90-2.80 (several m, 4H, H4+H6), 2.81 (s, 1H, H8),
4.55 (m, 2H, H11+H14), 4.92 (m, 2H, H11+H14), 5.25 (m, 1H,
(3S,5R)- a n d (3R,5S)-1-Eth yn yl-3-h yd r oxy-2-m eth yl-5-
(p h en oxyca r bon yl)cycloh ex-1-en e (30 a n d 31). 1H NMR
(CDCl3, 200 MHz): δ 1.90 (br s, 1H, OH), 2.05 (s, 3H, H9),
2
3
2.11 (m, 2H, H4), 2.41 (dd, 1H, H6, J HH ) 17.2, J HH ) 7.0
2
3
Hz), 2.76 (dd, 1H, H6, J HH ) 17.2, J HH ) 5.0 Hz), 3.14 (s,
1H, H8), 4.34 (br s, 1H, H3), 5.14 (m, 1H, H5), and 7.15-745

4232 J . Org. Chem., Vol. 66, No. 12, 2001
D´ıaz et al.
(m, 5H, ArH); HRMS (EI, m/z) Calcd. for C16H16O4: 272.1049.
Found: 272.1050.
m/z): 251 (M + , <1%), 134 (19), 119 (23), 91 (60), and 156
(100).
(3S,5S)- a n d (3R,5R)-1-Eth yn yl-3-h yd r oxy-2-m eth yl-5-
(p h en oxyca r bon yloxy)cycloh ex-1-en e (32a a n d 33a ). H
1
Ack n ow led gm en t. We express our appreciation to
Novo Nordisk Co. for the generous gift of the lipase
CAL-B. Financial support from CICYT (Spain; Project
BIO98-0770) is gratefully acknowledged. S. F. also
thanks the Ministerio de Educacio´n y Cultura (Spain)
for her postdoctoral fellowship.
NMR (CDCl3, 200 MHz): δ 1.70 (br s, 1H, OH), 2.09 (s, 3H,
2
3
H9), 2.13 (m, 1H, H4), 2.30 (ddd, 1H, H4, J HH ) 14.6, J HH
)
3
6.4, J HH ) 4.1 Hz), 2.59 (m, 2H, H6), 3.16 (s, 1H, H8), 4.13
(m, 1H, H3), 5.17 (m, 1H, H5), 7.15-7.45 (m, 5H, ArH); MS
(ESI+, m/z): 272 [M]+, 295 [M + Na]+, and 311 [M + K]+.
(3S,5S)- a n d (3R,5R)-1-Eth yn yl-3-h yd r oxy-2-m eth yl-5-
[(a cet on oxim e)ca r b on yloxy]cycloh ex-1-en e (32b a n d
33b): 1H NMR (CDCl3, 200 MHz): δ 1.98 (s, 3H, H12), 1.99
(s, 3H, H12), 1.97-2.10 (m, 1H, H4), 2.05 (br s, 3H, H9), 2.24
(dddd, 1H, H4, 2J HH ) 14.4, 3J HH ) 5.9, 3J HH ) 3.6, 4J HH ) 1.0
Hz), 2.41-2.67 (m, 2H, H6), 2.70 (br s, 1H, OH), 3.11 (s, 1H,
H8), 4.06 (m, 1H, H3), and 5.20 (m, 1H, H5).); MS (70 eV,
Su p p or tin g In for m a tion Ava ila ble: Complete 1H and
13C NMR spectral data in addition to mp, IR, microanalysis,
and MS data. This material is available free of charge via the
Internet at http://pubs.acs.org.
J O010017F