Enzymatic desymmetrization of prochiral 2-substituted-1,3-propanediols: A practical chemoenzymatic synthesis of a key precursor of SCH51048, a broad- spectrum orally active antifungal agent

Article abstract of DOI:10.1021/jo9709920

Two examples of a practical enzymatic desymmetrization of a 2- substituted-1,3-propanediol and their application to the synthesis of SCH51048, a broad-spectrum orally active antifungal, are described. In each case, enzymatic catalysis under both hydrolytic and transesterification conditions is described. In the first example the key intermediate, the R,S- monoester of triol 6, was obtained via Amano Lipase AK catalyzed hydrolysis of the dibutyrate 11b, or Novo SP435 catalyzed acetylation of triol 6. In the second example, desymmetrization of diol 13a using Novo SP435 or of dibutyrate 13c using Amano Lipase CE furnished the S-monoester (S)-14b,c, a key intermediate in a new efficient synthesis of SCH51048. Optimization of the Novo SP435 acetylation of diol 13a and the scaleup of the reaction is also described.

Full text of DOI:10.1021/jo9709920

7736
J . Org. Chem. 1997, 62, 7736-7743
En zym a tic Desym m etr iza tion of P r och ir a l
2-Su bstitu ted -1,3-p r op a n ed iols: A P r a ctica l Ch em oen zym a tic
Syn th esis of a Key P r ecu r sor of SCH51048, a Br oa d -Sp ectr u m
Or a lly Active An tifu n ga l Agen t
Brian Morgan,*,† David R. Dodds,† Aleksey Zaks,† David R. Andrews,‡ and Ricardo Klesse‡
Schering-Plough Research Institute, Biotransformations Group, K-15-1/ 1800, 2015 Galloping Hill Road,
Kenilworth, New J ersey 07033-0539, and Chemical Process R & D, 1011 Morris Avenue,
Union, New J ersey 07083
Received J une 3, 1997X
Two examples of a practical enzymatic desymmetrization of a 2-substituted-1,3-propanediol and
their application to the synthesis of SCH51048, a broad-spectrum orally active antifungal, are
described. In each case, enzymatic catalysis under both hydrolytic and transesterification conditions
is described. In the first example the key intermediate, the R,S-monoester of triol 6, was obtained
via Amano Lipase AK catalyzed hydrolysis of the dibutyrate 11b, or Novo SP435 catalyzed
acetylation of triol 6. In the second example, desymmetrization of diol 13a using Novo SP435 or
of dibutyrate 13c using Amano Lipase CE furnished the S-monoester (S)-14b,c, a key intermediate
in a new efficient synthesis of SCH51048. Optimization of the Novo SP435 acetylation of diol 13a
and the scaleup of the reaction is also described.
Ch a r t 1
In tr od u ction
SCH51048 (1) was identified as a potential antifungal
agent with efficacy in the treatment of systemic Candida
and Aspergillus infections in both normal and immuno-
compromised models.1 In common with other azole
antifungals (Chart 1), SCH51048 (1) contains the het-
erocyclic ring, a dihalogenobenzene ring and a rigid side
chain, distributed around a central five-membered ring.
Unlike Ketoconazole (2), Itraconazole (3) and Sapercona-
zole (4), which contain a central 1,3-dioxolane ring,
SCH51048 contains a central tetrahydrofuran ring which
confers increased efficacy.1e Construction of this 2,2,4-
trisubstituted ring with the required stereochemistry
presented a synthetic challenge.
The initial approach1c introduced chirality (88-92% ee)
via a Sharpless-Katsuki epoxidation2 of the allyl alcohol
5. A series of further reactions yielded the desired R-triol
6, in which the enantiomeric excess had been enhanced
to >98%. Tosylation of the two primary hydroxyls then
gave ditosylate 7 (Scheme 1).
hydroxyls by the tertiary hydroxyl under basic conditions
(path a or b in Scheme 1). However, under all tested
conditions, it was the undesired 2R,4R-trans isomer 8b
which predominated (60 trans:40 cis), and isolation of the
desired 2R,4S-cis isomer 8a required careful chromatog-
raphy (25-30% yield from the triol 6). Clearly the yield
of the desired material could only be maximized by
differentiation of the two primary hydroxyls prior to
cyclization to the tetrahydrofuran ring. If the pro-S
hydroxyl group of triol 6 could be blocked, tosylation and
cyclization would then yield the required 2R,4S-cis
isomer 8a .3 Since triol 6 is a 2-substituted-1,3-pro-
panediol, enzymatic desymmetrization suggested itself
as a convenient method to differentiate between the two
primary alcohols.4
The tetrahydrofuran ring could now be formed via
nucleophilic stereoselective displacement of one of the two
* Author to whom correspondence should be addressed. Phone: 908
298 7637; e-mail: william.brian.morgan@spcorp.com.
† Biotransformations Group.
‡ Chemical Process R & D.
X Abstract published in Advance ACS Abstracts, September 15, 1997.
(1) (a) 34th Interscience Conference on Antimicrobial Agents and
Chemotherapy (ICAAC), Orlando, Florida, 4-7th October 1994. (Ab-
stract Nos. B16, F181, F183, F185, F187, F193, F195, F197 B179). (b)
Blundell, P.; Ganguly, A. K.; Girijavallabhan, V. M. Synlett 1994, 263-
265. (c) Saksena, A. K.; Girijavallabhan, V. M.; Lovey, R. G.; Pike, R.
E.; Desai, J . A.; Ganguly, A. K.; Hare, R. S.; Loebenberg, D.; Cac-
ciapuoti, A.; Parmegiani, R. M. Biorg. Med. Chem. Lett. 1994, 4, 2023-
2028. (d) Lovey, R. G.; Saksena, A. K.; Girijavallabhan, V. M.
Tetrahedron Lett. 1994, 35, 6047-6050. (e) Saksena, A. K.; Girijav-
allabhan, V. M.; Lovey, R. G.; Desai, J . A.; Pike, R. E.; J ao, E.; Wang,
H.; Ganguly, A. K.; Loebenberg, D.; Hare, R. S.; Cacciapuoti, A.;
Parmegiani, R. M. Biorg. Med. Chem. Lett. 1995, 7, 127-132. (f) A
preliminary report of some of this work has appeared previously:
Saksena, A. K.; Girijavallabhan, V. M.; Lovey, R. G.; Pike, R. E.; Wang,
H.; Ganguly, A. K.; Morgan, B.; Zaks, A.; Puar, M. S. Tetrahedron Lett.
1995, 36, 1787-1790. (g) Saksena, A. K.; Girijavallabhan, V. M.; Pike,
R. E.; Wang, H.; Lovey, R. G.; Liu, Y.-T.; Ganguly, A. K.; Morgan, W.
B.; Zaks, A. US Patent 5,403,937, April 4, 1995.
(3) Blocking the pro-S hydroxyl of triol 6, followed by tosylation,
cyclization, deblocking, and tosylation would result in
a five-step
sequence to cis tosylate 8a . Alternatively, blocking the pro-R hydroxyl
would require a seven-step sequence to 8a because of the extra steps
to invert the 2R chiral center. Pro-R hydrolysis of the triol diester 10
or 11 would require six steps to 8a .
(4) (a) Ramos Tombo, G. M.; Schar, H.-P.; Fernandez i Busquets,
X.; Ghisalba, O. Tetrahedron Lett. 1986, 27, 5707-5710. (b) Boland,
W.; Fro¨ssl, C.; Lorenz, M. Synthesis 1991, 1049-1072. (c) Danieli, B.;
Lesma, G.; Passerella, D.; Riva, S. In Adv. Use Synthons Org. Chem.
1993, 1, 143-219. (d) Schoffers, E.; Golebiowski, A.; J ohnson, C. R.
Tetrahedron 1996, 52, 3769-3826.
(2) Katsuki, T.; Sharpless, K. B. J . Am. Chem. Soc. 1980, 102, 5974-
5976.
S0022-3263(97)00992-4 CCC: $14.00 © 1997 American Chemical Society

Enzymatic Desymmetrization of Prochiral 1,3-Propanediols
Sch em e 1
J . Org. Chem., Vol. 62, No. 22, 1997 7737
Sch em e 2
agents, but no conditions were found to improve the
diastereoselectivity.
Since a highly selective pro-S enzyme had not been
identified, further work was undertaken with Amano
Lipase AK, the most selective of the pro-R enzymes. Two
approaches were possible.
(i) Acyla tion : Pro-R acetylation provided the monoac-
etate (R,R)-9 in high de,6 but a subsequent protection/
deacylation sequence was required to invert the newly
formed R-chiral center, resulting in a seven-step sequence
from R-triol 6 to the cyclized cis tosylate 8a .3
(ii) Hyd r olysis: Since lipases generally display the
same prochiral selectivity for acylation and hydrolysis
reactions, Lipase AK catalyzed hydrolysis of the diacetate
10 would provide the desired monoacetate (R,S)-9 in an
overall six-step sequence from R-triol to cis tosylate 8a .
Initial hydrolyses in phosphate buffer yielded monoac-
etate (R,S)-9 with low de, so the effect of cosolvents, both
miscible and immiscible, was examined. For miscible
solvents the best de’s were observed with 10-20% THF;
when increased to 50% THF no reaction was observed.
With 5% MeCN or 10% acetone the reaction was slower
and less selective. Of the ether solvents, the best results
were obtained with 20% Et2O; 20% iPr2O and 30% TBME
resulted in product of low de.
The hydrolysis of a series of diesters was examined in
10-20%THF/50 mM KCl (pH 7.0) (Table 2). While the
R,S-monoesters were formed with high de, the selectivity
was poor and substantial amounts of overhydrolysis to
triol occurred before complete consumption of starting
material.
Nevertheless, hydrolysis of the dibutyrate 11a was a
convenient process, not only because of its high initial
rate. Due to its low water solubility, the monobutyrate
12a could be partially purified after the enzymatic step;
aqueous extraction of the crude product preferentially
removed the more water soluble triol 6 which was formed
by over hydrolysis. Furthermore, the chemical acylation
and enzymatic hydrolysis reactions could be carried out
in a one-pot reaction. When butrylation of the triol 6 in
Resu lts a n d Discu ssion
A. Desym m et r iza t ion of Tr iol 6. The enzymatic
acetylation of triol 6 in neat methyl acteate using porcine
pancreatic lipase (PPL Sigma Type II) had been previ-
ously reported to display pro-R selectivity to give (R,R)-9
(Scheme 2), and six subsequent steps were required to
arrive at the desired 2R,4S-cis tosylate 8a .1d,3 However,
in our hands under the reported conditions, this acylation
resulted in a mixture of diol, diacetate, and monoacetate
with marginally useful diastereomeric excess (85-90%
de).
Lipases generally display the same prochiral selectivity
for the acylation of 2-substituted-1,3-propanediols and for
the hydrolysis of the corresponding diesters. As a result,
products of opposite absolute stereochemistry may be
obtained using the same enzyme under either acylating
or hydrolytic conditions (Scheme 2).4b Consequently, the
PPL-catalyzed hydrolysis of the diesters 10 and 11b was
examined.3 However the reaction showed poor selectiv-
ity. Extensive overhydrolysis to triol 6 occurred and the
monoester 9 was formed in poor de. Furthermore
prochiral selectivity varied with reaction conditions.5
A screen of our enzyme collection was undertaken to
identify enzymes showing high pro-S selectivity for the
acylation of triol 6. Of the 86 commercially available
enzyme preparations which were initially tested, 16
showed significant pro-R selectivity, using vinyl acetate
(10 equiv) as acylating agent in EtOAc (Scheme 3). These
gave the less desired monoacetate ((R,R-9), in some cases
with moderate to high diastereomeric excess (Table 1).
The 12 enzymes which showed the desired pro-S selectiv-
ity all suffered from low selectivity and/or rate of acyla-
tion. From these 12, Amano Lipase R (yielding the
(R,S)-9 isomer in 78% de at 20% conversion) was chosen
for a study of different solvents and different acetylating
(5) The acylation of 6 and the hydrolysis of 10, 11b varied with
enzyme lot and with the nature of the acyl group. Using Sigma PPL
Type II, lot no. 23H0294 was more reactive than lot no. 41H0954 under
acylation conditions. With both enzyme samples butyrylation (10 equiv
of trifluoroethyl butyrate in TBME; 2× enzyme) was faster than
acetylation (neat MeOAc; 3× enzyme); however the R,R-monoester was
formed in poor de under both conditions. Under hydrolytic conditions
(10 mM phosphate buffer; pH 7; 10% THF, 10% MeCN or 50% TBME
as cosolvent) lot no. 41H0954 was more reactive than lot no. 23H0294.
Hydrolysis of the diacetate 10 yielded the expected R,S-monoacetate
9 with generally poor de. For hydrolysis of the dibutyrate 11b under
the same conditions, lot no. 23H0294 showed poor reactivity (10%
conversion in 10%MeCN/buffer and 4% conversion in 50%TBME/buffer
after 6h) but produced the expected R,S-monobutyrate 12b. In contrast,
lot no. 41H0954 produced the R,R-monobutyrate under all hydrolytic
conditions tested, albeit in poor yield.
(6) After 2 h, a mixture of triol 6 (6.5 g), vinyl acetate (10 equivs),
and lipase AK (6.6 g) in EtOAc (150 mL) showed a 6:9:10 ratio of 1:98:
1. After workup (R,R)-9 was obtained in 81% yield (97% de; [R]21D -17.7
(c 0.46, MeOH); lit.1d [R]21 -17.8 (c 1, MeOH))
D

7738 J . Org. Chem., Vol. 62, No. 22, 1997
Morgan et al.
Sch em e 3
Ta ble 1. Acetyla tion of Tr iol 6. Scr een Resu ltsa
Enzyme
time, h
% triol 6
% monoacetate 9
% diacetate 10
% de
P r o-R Acyla tin g En zym es
Amano Lipase AK (Pseudomonas sp.)
Novo Lipozyme (Mucor miehei)
21
21
21
21
21
21
19
0
0
0
1
0
92
53
76
97
98
69
94
8
47
24
2
2
0
98.1
93.5
92.4
92.1
85.7
84.3
84.0
Amano Lipase PS-30 (Pseudomonas fluorescens)
Amano Lipase CES (Pseudomonas sp.)
Sigma Porcine Pancreatic Lipase Type II
Solvay Porcine Pancreatic Lipase
Biocatalysts P. fluorescens
31
1
5
P r o-S Acyla tin g En zym es
Amano Lipase R (Penicillium roquefortii)
Interspex Bacterial Lipase/Esterase
Amano Newlase A (Aspergillus. niger)
Quest Acid Protease 200,000
Meito OF (Candida cylindracea)
Sigma Protease Type IV (Streptomyces caespitosus)
Amano Lipase G (Penicillium camembertii)
Biocatalysts C. cylindracea
Biocatalysts P. ciclopium
Enzeco Fungal Acid Protease
Sigma Protease Type XXIV
Solvay AFP 2000
21
48
49
49
21
49
21
21
21
48
49
48
83
55
39
78
41
67
43
82
87
32
80
2
17
39
58
21
56
32
57
18
9
0
5
3
0
3
0
0
0
4
77.6
73.5
72.1
56.7
55.5
54.3
36.1
33.8
31.3
26.2
23.6
21.5
64
18
75
3
2
23
a
Conditions: triol 6 (0.11-0.16 mmol), vinyl acetate (7-43 equiv), EtOAc 1.0 mL, enzyme 8-180 mg, 250 rpm, rt.
Ta ble 2. Hyd r olysis of Diester s 10 a n d 11a -d w ith Lip a se AKa
%
%
%
initial rate
R
cosolvent
time, h
triol
monoester
diester
% de
µmol/h/mg enzyme
10
CH3
CH2CH2CH3
CH(CH3)2
10% THF
10% THF
20% THF
20% THF
48
3
49
6
17
5
10
16
57
57
81
64
26
38
9
97.0
96.7
95.9
>98
0.03
0.46
0.03
0.17
11a
11b
11c
(CH2)4CH3
20
a
Conditions: diester (60-100 mg); enzyme (60-100 mg)(except for 10, 300 mg); 50 mM aqueous KCl; pH 7.0; rt.
THF was complete, the entire reaction mixture was
diluted 10 fold with 50 mM KCl, the pH adjusted to 7.0,
and the enzyme added. From this reaction mixture, the
monobutyrate 12a was obtained (Scheme 4), essentially
free of triol, in good yield (64%) with 99% de.
(iii) P r o-S Acyla tion : As the hydrolysis of the dibu-
tyrate 11b was being developed, an enzyme displaying
useful levels of the desired pro-S selectivity was finally
identified. Treatment of triol 6 with Novo SP435 in
EtOAc or MeCN with vinyl acetate as acylating agent
resulted in formation of (R,S)-9 with 94-97% de (Table
3).
from a enzymatic desymmetrization of diol 13a could be
used to control the stereochemistry of the iodocyclization
reaction, forming predominantly the cis iodide 15 and
leading ultimately to the desired (R,S)-tosylate 8a .7
From an initial screen of 53 hydrolases, 3 enzyme
preparations were found to provide the monoacetate 14b
with high enantiomeric excess (Table 4). The screen was
subsequently extended, and a total of 205 commercial
enzyme preparations have been examined under similar
conditions; only one other enzyme preparation, Chira-
zyme L-2 (Boehringer-Mannheim),8 displayed high pro-S
selectivity.
B. Im p r oved Rou te to Tosyla te 8a . Before either
the acylation or hydrolysis routes to the key monoesters
9, 12 could be exploited, a more efficient route to cis
tosylate 8a was identified.1f In this sequence (Scheme
5) the tetrahydrofuran ring is formed via an iodocycliza-
tion reaction from diol 13a . A 2S chiral center resulting
(7) Acylation of the pro-S hydroxyl of 13a would result in a five-
step sequence to cis tosylate 8a (acylation, iodocyclization, triazole
introduction, deacylation, and tosylation), while pro-R acylation would
require two extra steps to invert the 2R chiral center. Pro-R hydrolysis
of the diester 13a ,b would result in a six-step sequence to 8a .
(8) Both Novo SP435 and Boehringer-Mannheim Chirazyme L-2 are
immobilized forms of Lipase Type B from Candida antarctica.

Enzymatic Desymmetrization of Prochiral 1,3-Propanediols
J . Org. Chem., Vol. 62, No. 22, 1997 7739
Sch em e 4
Sch em e 5
Ta ble 3. Acetyla tion of Tr iol 6 w ith Novo SP 435a
Sch em e 6
time, % triol % monoacetate % diacetate
run solvent min
6
9
10
% de
1
2
EtOAc
MeCN
75
55
5
4
83
95
12
1
94.0
96.6
a
Conditions: run 1: triol 64 mg, enzyme 15 mg, EtOAc1 mL,
vinyl acetate 10 equiv. Run 2: triol 0.5 g, SP435 51 mg, MeCN 5
mL, vinyl acetate 2 equiv, rt.
Ta ble 4. Acetyla tion of Diol 13a : In itia l Scr een Resu ltsa
time,
min
% diol
13a
% monoacetate
% diacetate
enzyme
Lipase SP435 (Novo)
Lipase CE (H. lanuginosa) (Amano)
Lipase H. lanuginosa (Biocatalysts Ltd.)
14b
13b
% ee
pref
60
95
220
0
0
1
83
97
98
17
3
1
97
99
98
pro-S
pro-R
pro-R
a
Conditions: diol 50 mg; enzyme 10-200 mg; vinyl acetate 10 equivs; toluene 1.0 mL; rt.
The availability of two enzymes with opposite prochiral
selectivity allowed three approaches to the preparation
of the desired S-monoester precursor.
lower than for Lipase CE (kS1/kR ≈ 20), optical purity
1
was purchased at the cost of chemical yield, and a
significant amount of the diacetate 13b had to be formed
before the ee of the remaining monoacetate 14b reached
useful levels (Scheme 6 and Figure 1).9
(i) Pro-R acetylation of diol 13a using Lipase CE gave
the monoacetate (R)-14b with high chemical and optical
yield. As the reaction profile indicated, kR1 >> kS1 or kS
Nevertheless, because it provided the S-monoester
directly under operationally simple conditions, the SP435
catalyzed acetylation of diol 13a was selected for opti-
mization.
2
(Scheme 6). However, protection/deacylation was re-
quired to invert the chiral center, resulting in a seven-
step sequence from diol 13a to tosylate 8a .7 Since
attempts to introduce a tetrahydropyranyl protecting
group resulted in significant racemization, presumably
via 1,3 acyl migration, this route was not pursued and
was only used to prepare small quantites of (R)-14b.
(ii) Lipase CE catalyzed pro-R hydrolysis of the diester
Ironically, the first problem was not improvement, but
reproduction of the favorable results from the initial
screen. Diol 13a is prepared by reduction of the corre-
sponding 2-substituted diethyl malonate and samples
from different sources (LiAlH4 vs NaBH4/LiCl reduction,
chromatographically pure vs crude product) displayed
different reaction rates and selectivities. The different
reaction rates were attributed to moisture in the samples,
since the rate of diol consumption could be decreased by
addition of small amounts of water, while molecular
sieves increased the rate.
would yield the S-monoester (kR >> kS-2), for a six-
-2
step sequence from diol 13a to tosylate 8a .7 While
hydrolysis of the dibutyrate 13c produced the monobu-
tyrate (S)-14c with high enantiomeric excess, the chemose-
lectivity was poor, and the reaction mixture consisted of
a mixture of diol 13a , dibutyrate 13c, as well as the
desired monoester (S)-14c.
More disturbing was the observation that, for certain
samples, significant amounts of diol remained uncon-
sumed, even though the reaction was run out to high
diacetate formation.
(iii) SP435 catalyzed pro-S acetylation of diol 13a
provided (S)-14b directly for a five-step route to tosylate
8a .7 Because the prochiral selectivity of this enzyme is

7740 J . Org. Chem., Vol. 62, No. 22, 1997
Morgan et al.
Sch em e 7
Ta ble 6. P r od u ct Distr ibu tion a n d En a n tiom er ic Excess
a t >94% Diol Con ver sion in Va r iou s Solven tsa
product distribution (%)
diol/
vinyl enzyme
mono-
di-
acetate ratio time diol acetate acetate % ee
run solvent equiv
(w/w) (min) 13a
14b
13b
(S)
1
2
3
4
5
6
7
8
iPr2O
THF
dioxane 10.0
acetone 10.0
iPrOAc
tBME
MeCN
toluene
10.0
10.0
4.0
4.0
4.0
4.0
9.0
9.0
4.0
4.0
90
120
90
6
2
1
1
1
3
1
1
84
77
75
83
78
75
85
85
10
22
24
16
21
22
14
14
91
90
93
94
97
94
96
96
F igu r e 1. Acylation of 13a with Novo SP435: Diol, 50 mg;
SP435, 10 mg; vinyl acetate, 10 equiv; toluene, 1.0 mL; rt.
90
Ta ble 5. In com p lete En zym a tic Acetyla tion a
2.0
2.0
5.0
5.0
260
226
60
product
distribution (%)
vinyl diol/enzyme
120
acetate
ratio
time diol monoacetate diacetate
run solvent equiv
(w/w)
(min) 13a
14b
13b
a
Conditions: diol 50 mg; solvent 1.0 mL; 0 °C (except run 3,
1
2
3
4
toluene
MeCN
MeCN
MeCN
2.2
2.2
5.0
5.0
10
10
4.4
4.4
175 90
105 93
1080 46
1170 35
10
7
38
32
0
0
17
33
20 °C).
the selectivity of SP435 is not absolute and the enantio-
meric excess of the monoacetate (S)-14b increases over
the course of the reaction, albeit at the expense of
chemical yield, the question was what compromise should
be struck between optical and chemical yield. Like the
S-monoacetate 14b, unreacted diol 13a also undergoes
iodocyclization to yield racemic material 16 (Scheme 7)
which, if carried forward would dilute the optical purity
of the key precursor, cis tosylate 8a . The diester 13b
was shown not to react and may be recovered as the diol
at a subsequent stage.
While minimization of both diol and diester would be
desireable, it is more important that the amount of
unreacted diol be minimized. At the outset it was not
clear how much of the wrong enantiomer could be purged
in the subsequent steps to SCH51048, so the following
specification was applied: the acetylation would be
monitored until the enantiomeric excess of the S-monoac-
etate 14b was >95% with <2% diol 13a remaining.
With this constraint the effect of temperature, solvent,
acylating agent, and substrate and enzyme loading on
the SP435 catalyzed acetylation of diol 13a was exam-
ined. Decreasing the temperature to 0 °C slowed the
reaction in toluene, but yielded monoacetate 13b in
higher optical purity.
a
Conditions: diol, 0.5 g; SP435, 50 mg; solvent, 10 mL; 0 °C.
For one sample (Table 5, runs 1-3) the reaction was
sluggish in both toluene and MeCN at 0 °C, with <10%
reaction after 2-3 h. Despite increasing the amount of
enzyme, acylating agent, and reaction time, 46% of the
diol 13a remained, even though 17% diacetate 13b had
been formed. Similar results were observed with a
second sample (run 4). 1H NMR (DMSO-d6) examination
of the crude reduction product revealed that a significant
amount of diol 13a was complexed as a borate ester (from
NaBH4 reduction of the malonate ester) and was un-
available for reaction under the reaction conditions.10,11
(During HPLC analysis (5%EtOH/hexane) transesterifi-
cation of the borate ester revealed the unreacted diol.)
Refluxing the partially complexed diol with AcOH/MeOH,
removal of trimethyl borate by distillation, and crystal-
lization from toluene resulted in a product which under-
went enzymatic acetylation reproducibly without inci-
dent.
With a secure supply of boron-free, crystallized diol
13a , optimization of the reaction was examined. Since
For a series of solvents the reaction mixture composi-
tions were compared when ∼2% diol remained (Table 6).12
The best results were obtained with toluene, MeCN, and
(9) Wang, Y.-F.; Chen, C.-S.; Girdaukas, G.; Sih, C. J . J . Am. Chem.
Soc. 1984, 106, 3695-3696.
(10) While boronic acids are well known reversible inhibitors of
serine proteases (J ones, J . B.; Martichonok, V. J . Am. Chem. Soc. 1996,
118, 950-958 and refs 14,15 therein), we are unaware of reports of
borate esters as inhibitors. However, the fact that diacetate 13b
continued to be produced while diol 13a apparently remained uncon-
sumed, suggested that the borate ester does not inhibit Novo SP435.
(11) Subsequent acylations which were doped with increasing
amounts of trimethyl borate resulted in a corresponding increase in
the amount of unreacted diol. 1H NMR and mass spectrometry
confirmed the presence of the cyclic borate ester (see Supporting
Information).
(12) Unlike Novo SP435, Lipase CE catalyzed acetylation showed
a pronounced solvent dependence. From a comparison of 10 common
solvents, the reaction was fastest in neat vinyl acetate, toluene, or
tBME. As for SP435, the Lipase CE acetylation was very slow in
isopropenyl acetate at room temperature, but unlike SP435 the reaction
was also very slow in MeCN. Furthermore, excess vinyl acetate was
required for reasonable reactivity; at 1.5-2.0 equiv of vinyl acetate
the reaction was considerably slower.

Enzymatic Desymmetrization of Prochiral 1,3-Propanediols
J . Org. Chem., Vol. 62, No. 22, 1997 7741
Sch em e 8
iPrOAc all of which showed ee > 0.97 with <2% diol
remaining. Acetone, tBME, and dioxane were less useful,
and THF, iPr2O, and tert-amyl alcohol (results not shown)
gave poor selectivity. MeCN was selected as the reaction
solvent since the subsequent iodocyclization step was also
carried out in MeCN at 0 °C, and the prospect of simply
removing the enzyme beads by filtration and carrying out
the iodocyclization on the crude reaction mixture was
especially attractive.
A range of acylating agents was surveyed, either neat,
or in toluene or MeCN solution. The best results were
obtained with vinyl acetate or acetic anhydride. Since
vinyl acetate releases acetaldehyde during transesteri-
fication, there was concern whether the recovery and
reuse of the enzyme would be compromised.13 Isoprope-
nyl acetate, which releases acetone upon transesterifi-
cation, was examined under similar conditions, but was
less reactive. When alkyl acetates (Me, Et, iPr) were
used as both acylating agent and solvent, the reactions
reached equilibrium before diol consumption was com-
plete, and the monoacetate 13b was produced with low
ee. With MeOAc in the presence of molecular sieves
adsorption of the released MeOH shifted the equilibrium
toward the diacetate, and the monoacetate was formed
in high ee. None of the trifluoroethyl esters which were
tested were superior to vinyl acetate. Under similar
conditions, both trifluoroethyl acetate and butyrate were
slower than vinyl acetate and less readily available. It
was hoped that the use of a bulky acylating agent would
decrease diester formation and increase the selectivity
of the initial acylating event. Using trifluoroethyl isobu-
tyrate did suppress diester formation, but the monoester
was formed with low ee; even after extended reaction and
formation of diisobutyrate, the ee remained low. With
trifluoroethyl 2-methylbutyrate, diester formation was
completely suppressed, but the monoester was also
formed in very low ee. Vinyl butyrate was less selective
than, and offered no advantage over, vinyl acetate. Acetic
anhydride was similar to vinyl acetate in both reactivity
and selectivity, but presented some disadvantages. The
effect of released acetic acid and unconsumed anhydride
on the optical purity of the monoacetate was a concern,
because of the potential for 1,3 acyl migration under
acidic conditions or nonenzymatic acetylation. For batches
which must be stored after removal of the enzyme, an
aqueous extraction would be necessary to completely
remove acid and anhydride before the reaction mixture
could be used in the subsequent base-catalyzed iodocy-
clization. For operational simplicity, vinyl acetate was
retained as the acylating agent of choice.
Ta ble 7. Sca leu p of En zym a tic Acetyla tion
diol
% diol % monoacetate % diacetate
run
13a , kg
13a
S-14b
13b
% ee
1
2
9
33
2
<1
81
74
17
26
97a
99b
a
b
ee of (S)-14b. ee of (R,S)-15b.
(97% ee), but the rate of the reaction had slowed down
considerably. This decrease in rate was probably due
more to mechanical losses of enzyme during recycling
than to inactivation of the enzyme.
The conditions transferred to pilot plant for scaleup
were as follows: 20% diol 13a solution i.e., 200 g/L; 5%
Novo SP435 loading (w/w); 2.0 equiv of vinyl acetate;
industrial grade MeCN; 0 °C reaction temperature;
monoacetate specification: (S)-14b > 95% ee; <2% diol
13a remaining. A representative result is shown in Table
7 (run 1). The specifications for the enzymatic acylation
were subsequently tightened to produce monoacetate (S)-
14b of 98-99% ee with <1% unreacted diol remaining.
This could be achieved using the above conditions but
running the acetylation out to ∼30% diacetate formation
(Table 7, run 2).
Con clu sion
Optically enriched 2,2,4-trisubstituted tetrahydrofuran
(R,S)-15b is now prepared by an asymmetric synthesis,
the key steps of which are an enzymatic desymmetriza-
tion of a 2-substituted-1,3-propanediol and a subsequent,
efficient iodocyclization. The acetylation of diol 13a ,
catalyzed by Novo SP435, has shown itself to be a robust,
reproducible and economical step in the synthesis of
SCH51048. Further efforts to improve the prochiral
selectivity of this enzymatic conversion are in progress
and will be reported in due course.
Although ∼20% overreaction to the diester was re-
quired to furnish monoester of acceptable enantiomeric
excess, the reaction could be carried out with as little as
1.25 equiv of vinyl acetate. However, 1.4-2.0 equiv were
generally used to ensure low levels of diol. Diol concen-
tration was increased from 0.2 M in early reactions to
0.9 M (200 g/L) in MeCN, without any loss of perfor-
mance. Enzyme loading was decreased to 5% (w/w) and
could be decreased further to 1% with a corresponding
5-fold increase in reaction time.
Exp er im en ta l Section
Gen er a l. HPLC was carried out on a Waters 715 Ultra
Wisp. For triol 6 and related compounds the instrument was
equipped with a Zorbax Rx-C18 (50% MeOH/50 mM phosphate
buffer (pH 5.7) or 30% MeCN/H2O; 1 mL/min; 210 or 254 nm;
rt), a Novapak C18 column (Waters)(50% MeOH/20 mM
phosphate buffer (pH 7); 1 mL/min; 210 or 254 nm; rt), or a
YMC-Pack ODS-A column (40-50% MeCN/H2O; 1 mL/min;
215 nm; rt). Under all conditions the order of elution was triol,
(R,R)-monoester, (R,S)-monoester, and diester. For diol 13a
and related compounds the HPLC was equipped with a
Chiralpak AS column (Chiral Technologies Inc.) (5% EtOH/
hexane; 1.0 mL/min; 233 nm; rt). Optical rotations were
determined on a Perkin-Elmer 243 B Polarimeter. Flash
chromatography was carried out with Sorbisil C60 (40/60A)
or Selecto 32-63. All chemicals and enzymes were used as
received. Amano Lipase AK and Amano Lipase CE (Amano
To demonstrate enzyme recovery and reuse, a 50 mg
sample of SP435 was carried through 10 reaction cycles
over a period of 14 days. After 10 cycles the enzyme
sample still produced monoacetate of acceptable quality
(13) Weber, H. K.; Stecher, H.; Faber, K. Biotechnol. Lett. 1995, 17,
803-808.

7742 J . Org. Chem., Vol. 62, No. 22, 1997
Morgan et al.
International Enzyme Co.) are prepared by fermentation of a
selected strain of Pseudomonas sp. and Humicola lanuginosa,
respectively. Novo SP435 (Novozyme 435 from Novo Nordisk)
is a lipase (Lipase Type B) whose gene coding has been
transferred from a selected strain of Candida antarctica to a
host organism, Aspergillus oryzae. The enzyme produced by
the host organism is immobilized on a macroporous acrylic
resin.
3.64 (dd, 1H, J ) 10 Hz and 3 Hz), 3.80 (m 2H,), 4.50 (d, 1H,
J ) 14 Hz), 4.57 (d, 1H, J ) 14 Hz), 6.83 (m, 2H), 7.54, (m,
1H), 7.75 (s, 1H), 8.14 (s, 1H); 13C NMR (75 MHz, CDCl3) δ
3
4
20.76, 36.25, 37.92 (d, J C,F ) 4 Hz), 58.48 (d, J C,F ) 4 Hz),
4
2
63.12, 65.39, 74.28 (d, J C,F ) 5 Hz), 104.18 (t, J C,F ) 27 Hz),
2
4
2
111.49 (dd, J C,F ) 20 Hz, J C,F ) 3Hz), 125.14 (dd, J C,F ) 14
4
3
Hz, J C,F ) 4 Hz), 130.52 (dd, J C,F ) 6 Hz and 9 Hz), 144.39,
1
3
150.48, 158.66 (dd J C,F ) 247 Hz, J C,F ) 12 Hz), 162.68 (dd
1J C,F ) 250 Hz, J C,F ) 12 Hz), 171.11; MS (CI + CH4)(m/z)
3
(2′R)-2-[2′-(2′′,4′′-Diflu or oph en yl)-2′-h ydr oxy-3′-(1′′,2′′,4′′-
tr ia zolyl)p r op yl]-1,3-d ia cetoxyp r op a n e (10). A solution
of Et3N (10.0 mL, 71.7 mmol) in THF (10 mL) was added
dropwise over a period of 10 min to a solution of triol 61d (6.06
g, 19.34 mmol) and acetic anhydride (4.5 mL, 47.7 mmol) in
THF (100 mL). After stirring for 24 h at room temperature,
most of the THF was removed, and the residue was dissolved
in EtOAc (100 mL), washed with saturated NaHCO3 (2 × 50
mL), water (100 mL), and saturated NaCl (50 mL), dried
(MgSO4), filtered, and evaporated to obtain a yellow viscous
356 (M + 1)(100%), 338 (25), 296 (16), 213 (3). Anal. Calcd
for C16H19F2N3O4: C, 54.08; H, 5.39; N, 11.83. Found: C,
54.14; H, 5.68; N, 11.64.
(2′R)-2-[2′-(2′′,4′′-Diflu or oph en yl)-2′-h ydr oxy-3′-(1′′,2′′,4′′-
tr ia zolyl)p r op yl]-1,3-d ibu tyr oxyp r op a n e (11b). A mix-
ture of triol 6 (5.99 g, 19.1 mmol), butyric anhydride (8.0 mL,
48.9 mmol), and DMAP (0.13 g, 1.1 mmol) in THF (100 mL)
was stirred at room temperature for 2.5 h. Most of the THF
was then removed in vacuo, and the residue was diluted with
EtOAc (100 mL), washed with saturated NaHCO3 (3 × 50 mL),
water (100 mL), and saturated NaCl (50 mL), dried (MgSO4),
filtered, and evaporated. The crude product was dried in a
vacuum oven at 80 °C overnight to yield a viscous yellow liquid
oil (6.43 g, 83.6%): [R]25 ) -21.1° (c 2.142, MeOH); IR (neat
D
on KBr) 3430 (b), 3120, 2959, 1739 (CdO), 1617, 1501, 1241,
1
1139, 1039, 967 cm-1; H NMR (300 MHz, CDCl3) δ 1.78 (dd,
1H, J ) 14 Hz and 7 Hz), 1.98 (s, 3H), 2.03 (s, 3H), 1.9-2.1
(m, 1H), 2.18 (dd, 1H, J ) 11 Hz and 3 Hz), 3.81 (m, 2H), 4.08
(dd, 1H, J ) 11 Hz and 7 Hz), 4.17 (dd, 1H, J ) 11 Hz and 5
Hz), 4.49 (d, 1H, J ) 14 Hz), 4.70 (d, 1H, J ) 14 Hz), 5.05 (bs,
1H; D2O exch), 6.80 (M, 2H), 7.51 (m, 1H), 7.82 (s, 1H), 7.93
(s, 1H); 13C NMR (75 MHz, CDCl3) δ 20.71, 20.86, 33.38, 35.30
(d, 3J C,F ) 4 Hz), 57.52 (d, 4J C,F ) 5 Hz), 64.54, 64.71, 75.55 (d,
(8.16 g, 94.1%): [R]25 ) -20.1° (c 2.060, MeOH); IR (neat on
D
NaCl): 3429 (bw), 3268 (bw), 3126 (bw), 2966, 2877, 1738
(CdO), 1617, 1500, 1459, 1420, 1273, 1179, 1139, 1092, 967,
1
851, 679 cm-1; H NMR (300 MHz, CDCl3) δ 0.91 (t, 3H, J )
7.4 Hz), 0.92 (t, 3H, J ) 7.4 Hz), 1.58 (sext, 2H, J ) 7.4 Hz),
1.62 (sext, 2H, J ) 7.4 Hz), 1.76 (dd, 1H, J ) 14.3 Hz and 7.3
Hz), 1.95 (sept, 1H), 2.14 (dd, 1H, J ) 14.4 Hz and 4.0 Hz),
2.19 (t, 2H, J ) 7.4 Hz), 2.26 (t, 2H, J ) 7.4 Hz), 3.81 (m, 2H),
4.12 (m, 2H), 4.47 (d, 1H, J ) 13.8 Hz), 4.69 (d, 1H, J ) 13.8
Hz), 5.00 (bs, 1H, D2O exch), 6.79 (m, 2H), 7.48, (m, 1H), 7.83
(s, 1H), 7.93 (s, 1H); 13C NMR (75 MHz, CDCl3) δ 13.63, 18.27,
2
2
4J C,F ) 5 Hz), 104.14 (t, J C,F ) 26 Hz), 111.74 (dd, J C,F ) 21
4
2
4
Hz, J C,F ) 3 Hz), 124.29 (dd, J C,F ) 13 Hz, J C,F ) 4 Hz),
130.17 (dd, 3J C,F ) 6 Hz and 9 Hz), 144.10, 151.79, 158.07 (dd,
1J C,F ) 248 Hz, 3J C,F ) 13 Hz), 162.72 (dd, 1J C,F )250 Hz, 3J C,F
) 13 Hz), 170.83, 171.18; MS (CI + CH4)(m/z) 398 (M +
1)(100%), 380 (14), 338 (27), 255 (5). Anal. Calcd for C18H21
-
3
18.37, 33.55, 35.40 (d, J C,F ) 4 Hz), 35.94, 36.07, 57.44 (d,
F2N3O5: C, 54.40; H, 5.33; N, 10.57. Found: C, 54.60; H, 5.66;
N, 10.48.
4
4J C,F ) 5 Hz), 64.33, 64.43, 75.69 (d, J C,F ) 5 Hz), 104.13 (dd,
2
4
2J C,F ) 26 Hz and 28 Hz), 111.76 (dd, J C,F ) 21 Hz, J C,F ) 3
(2R ,2′R )-2-[2′-(2′′,4′′-Diflu or op h e n yl)-2′-h yd r oxy-3′-
(1′′,2′′,4′′-tr ia zolyl)p r op yl]-1-a cetoxy-3-h yd r oxyp r op a n e
((R,R)-9). A mixture of triol 6 (2.05 g, 6.54 mmol), vinyl
acetate (3.0 mL, 32.5 mmol), and Amano AK (2.0 g) was stirred
in EtOAc (50 mL) at room temperature. After 190 min the
reaction was filtered, the enzyme cake washed with EtOAc
(10 mL), and the combined filtrate evaporated (<30 °C). The
residue was purified by column chromatography, eluting with
0-5% MeOH/CH2Cl2. The required fractions were pooled and
2
4
3
Hz), 124.28 (dd, J C,F ) 13 Hz, J C,F ) 4 Hz), 130.16 (dd, J C,F
1
) 6 Hz and 9 Hz), 143.98, 151.88, 158.31 (dd, J C,F ) 246 Hz,
3J C,F ) 12 Hz), 162.71 (dd, J C,F ) 251 Hz, J C,F ) 13 Hz),
173.33, 173.72; MS(CI + CH4)(m/z) 454 (M + 1)(30%), 394 (11),
366 (86), 283 (13), 89 (100). Anal. Calcd for C22H29F2N3O5:
C, 58.27; H, 6.45; N, 9.27. Found: C, 58.42; H, 6.85; N, 9.11.
1
3
(2S ,2′R )-2-[2′-(2′′,4′′-Diflu or op h e n yl)-2′-h yd r oxy-3′-
(1′′,2′′,4′′-t r ia zolyl)p r op yl]-1-b u t yr oxy-3-h yd r oxyp r o-
p a n e ((R,S)-12b). A solution of dibutyrate 11b (2.0 g, 4.41
mmol) in THF (3 mL) was added to 50 mM KCl (20 mL) in a
RB flask equipped with a magnetic stirrer and a pH electrode
and NaOH delivery tube connected to a pH stat. The mixture
was vigorously stirred and adjusted to pH 6.0. Amano AK
(0.40 g) was added and the pH maintained at 6.0 by constant
addition of 1 M NaOH. The reaction was stopped after 25 h
when 4.17 mL of 1 M NaOH (94.6% theoretical) had been
added. The reaction mixture was extracted with toluene (200
mL) which was then washed with water (2 × 50 mL), saturated
NaHCO3 (2 × 50 mL), and saturated NaCl (50 mL), dried
(MgSO4), filtered, and evaporated (<30 °C). The crude product
(1.16 g) was purified by column chromatography, eluting with
0-5% MeOH/CH2Cl2. The relevant fractions were pooled and
evaporated to obtain a foam (2.25 g, 96.6%; de 0.933: [R]25
)
D
-16.6° (c 1.47, MeOH); IR (neat on NaCl): 3289 (b), 3129,
2959, 1734 (CdO), 1617, 1500, 1420, 1368, 1271, 1139, 1090,
1
1038, 968, 852, 679 cm-1; H NMR (300 MHz, CDCl3) δ 1.91
(m,2H), 2.06 (s, 3H), 2.10 (m, 1H), 2.95 (bs, 1H; D2O exch),
3.38 (m, 2H), 4.13 (m, 2H), 4.50 (d, 1H, J ) 14 Hz), 4.72 (d,
1H, J ) 14 Hz), 5.30 (s, 1H; D2O exch), 6.79 (m, 2H), 7.49, (m,
1H), 7.80 (s, 1H), 7.94 (s, 1H); 13C NMR (75 MHz, CDCl3) δ
4
20.91, 36.51 (2C), 57.32 (d, J C,F ) 5 Hz), 62.95, 64.95, 75.29
4
2
2
(d, J C,F ) 5 Hz), 104.21 (t, J C,F ) 27 Hz), 111.66 (dd, J C,F
)
4
2
4
20 Hz, J C,F ) 3 Hz), 124.98 (dd, J C,F ) 13 Hz, J C,F ) 3 Hz),
129.91 (dd, 3J C,F ) 6 Hz and 9 Hz), 144.07, 151.62, 158.46 (dd,
3
1
1J C,F ) 258 Hz, J C,F ) 12 Hz), 162.66 (dd, J C,F ) 250 Hz,
3J C,F ) 12 Hz), 171.69; MS (CI + CH4)(m/z): 356 (M + 1)(100),
338 (37), 296 (20), 213 (8). Anal. Calcd for C16H19F2N3O4: C,
54.08; H, 5.39; N, 11.83. Found: C, 53.75; H, 5.69; N, 11.54.
(2S ,2′R )-2-[2′-(2′′,4′′-Diflu or op h e n yl)-2′-h yd r oxy-3′-
(1′′,2′′,4′′-tr ia zolyl)p r op yl]-1-a cetoxy-3-h yd r oxyp r op a n e
((R,S)-9). A mixture of triol 6 (2.0 g, 6.38 mmol), vinyl acetate
(1.4 mL, 13.06 mmol), and Novo SP435 (0.20 g) in MeCN (20
mL) was stirred at room temperature with continuous HPLC
monitoring. After 85 min the reaction mixture was filtered,
the enzyme beads washed with EtOAc (10 mL), and the filtrate
evaporated (<30 °C)(de 0.964). The crude product was purified
column chromatography, eluting with 0-6% MeOH/CH2Cl2.
The required fractions were pooled and evaporated to obtain
evaporated a colorless oil (1.00 g, 59.2%; de > 0.99): [R]25
)
D
-53.50° (c 1.013, MeOH); IR (neat on KBr): 3233 (b), 2965,
2878, 1734 (CdO), 1617, 1496, 1419, 1271, 1181, 1137, 966,
1
851, 679 cm-1; H NMR (300 MHz, CDCl3) δ 0.92 (t, 3H, J )
7.4 Hz), 1.60 (sext, 2H, J ) 7.4 Hz), 1.71 (m, 2H), 2.22 (t, 2H,
J ) 7.4 Hz), 2.43 (m, 1H, J ) 12.0 Hz and 2.2 Hz), 3.39 (dd,
1H, J ) 10.5 Hz and 7.3 Hz), 3.64 (dd, 1H, J ) 10.4 Hz and
3.6 Hz), 3.81 (m, 2H, J ) 5.4 Hz), 4.54 (s, 2H), 6.1 (bs, 1H,
D2O exch), 6.81 (m, 2H), 7.55, (m, 1H), 7.79 (s, 1H), 8.08 (s,
1H); 13C NMR (75 MHz, CDCl3) δ 13.66, 18.30, 35.97, 36.35,
3
4
37.61 (d, J C,F ) 4 Hz), 58.25 (d, J C,F ) 4 Hz), 63.41, 65.18,
4
2
74.71 (d, J C,F ) 5 Hz), 104.22 (dd, J C,F ) 26 Hz), 111.59 (dd,
2J C,F ) 21 Hz, J C,F ) 3 Hz), 124.28 (dd, J C,F ) 13 Hz, J C,F
)
4
2
4
a foam (2.04 g, 89.9%; de 0.966): [R]25 ) -49.19° (c 1.118,
D
3
4 Hz), 130.43 (dd, J C,F ) 6 Hz and 9 Hz), 144.31, 150.94,
MeOH); IR (neat on KBr) 3214 (b), 2930, 1739 (CdO), 1616,
1
3
1
1498, 1419, 1367,1245, 1137, 1041, 966, 853, 679 cm-1 1H
;
158.48 (dd, J C,F ) 247 Hz, J C,F ) 12 Hz), 162.72 (dd, J C,F
3
NMR (300 MHz, CDCl3) δ 1.70 (m,2H), 1.99 (s, 3H), 2.49 (dd,
1H J ) 2 Hz and 12 Hz), 3.34 (dd, 1H, J ) 10 Hz and 9 Hz),
)250 Hz, J C,F ) 13 Hz), 173.62; MS(CI + CH4)(m/z) 384 (M
+ 1)(100%), 366 (26), 296 (28), 213 (9), 89 (18). Anal. Calcd

Enzymatic Desymmetrization of Prochiral 1,3-Propanediols
J . Org. Chem., Vol. 62, No. 22, 1997 7743
for C18H23F2N3O4: C,56.39; H, 6.05; N, 10.96. Found: C, 56.27;
H, 6.20; N, 10.80.
13c (1.01, 2.74 mmol) in 0.1 M phosphate buffer (pH 7.8) (10
mL) was stirred in a three-neck flask equipped with a pH
electrode and a NaOH delivery line connected to pHstat.
Amano CE (1.0 g) was added and the mixture rapidly stirred,
maintaining pH 7.0 by automatic addition of 1 M NaOH. The
reaction was terminated after 18.25 h when 3.62 mL of NaOH
had been added. The reaction mixture was extracted with
hexanes (2 × 25 mL) and 40% MeOH/water (3 × 25 mL).
HPLC of the hexanes layer at this stage showed complete
removal of diol 13a . The hexanes layer was dried (MgSO4),
filtered, and evaporated (<30 °C) to obtain a colorless oil (0.43
g, 52.4%; ee 0.966): [R]24D ) -13.6° (c, 1.437, EtOH); IR (neat
on KBr): 3479 (b), 3082, 2965, 2875, 1735 (CdO), 1618, 1502,
(2S ,2′R )-2-[2′-(2′′,4′′-Diflu or op h e n yl)-2′-h yd r oxy-3′-
(1′′,2′′,4′′-t r ia zolyl)p r op yl]-1-b u t yr oxy-3-h yd r oxyp r o-
p a n e ((R,S)-12b). A solution of triol 6 (5.0 g, 16.0 mmol),
butyric anhydride (5.3 g, 33.6 mmol), and DMAP (0.14 g, 1.2
mmol) in THF (25 mL) was stirred at room temperature for
1.75 h, by which time TLC (5% MeOH/CH2Cl2) indicated
complete formation of the dibutyrate 11b. The reaction
mixture was diluted with 50 mM KCl (250 mL) and the
reaction flask equipped with a pH electrode and delivery tube
connected to a pH stat. With vigorous stirring the pH was
adjusted to and maintained at pH 7.0 by delivery of 1 M
NaOH. When pH had stabilized Amano AK (1.0 g) was added
and the mixture stirred at room temperature. The reaction
was terminated after 19.5 h when 17.4 mL of 1 M NaOH had
been delivered. The reaction mixture was extracted with
toluene (2 × 100 mL), and the combined organic extracts were
washed with water (4 × 100 mL) and saturated NaCl (50 mL),
dried (MgSO4), filtered, and evaporated to get a viscous oil
(3.94 g, 64.3%; de 0.994): [R]25D ) -51.1° (c 1.272, MeOH); IR
(neat on KBr): 3239 (b), 2966, 2878, 1735 (CdO), 1616, 1498,
1419, 1266, 1182, 1086, 970, 851 cm-1 1H NMR (300 MHz,
;
CDCl3): δ 0.94 (t, 3H, J ) 7.4 Hz), 1.64 (sext, 2H, J ) 7.4 Hz),
1.80 (m, 1H), 2.29 (t, 2H, J ) 7.4 Hz), 2.2-2.4 (bm, 1H, exch
D2O), 2.54 (sept, 2H), 3.46 (dd, 1H, J ) 11.3 Hz and 6.3 Hz),
3.54 (dd, 1H, J ) 11.3 Hz and 4.5 Hz), 4.08 (dd, 1H, J ) 11.2
Hz and 6.1 Hz), 4.16 (dd, 1H, J ) 11.2 Hz and 4.6 Hz), 5.12 (s,
1H), 5.27 (d, 1H, J ) 1.1 Hz), 6.76-6.88 (m, 2H), 7.24 (dt, 1H,
4J H,F ) 8.5 Hz and J H,H ) 6.5 Hz); 13C NMR (75 MHz, CDCl3):
4
δ 13.69, 18.46, 35.05 (d, J H,F ) 3 Hz), 36.15, 38.79, 62.06,
1419, 1271, 1181, 1135, 1092, 968, 852, 680 cm-1 1H NMR
;
63.63, 104.20 (t, 3J H,F ) 26 Hz), 111.34 (dd, 2J H,F ) 21 Hz, 4J H,F
(300 MHz, CDCl3) δ 0.92 (t, 3H, J ) 7.4 Hz), 1.62 (sext, 2H, J
) 7.4 Hz), 1.70 (m, 2H), 2.22 (t, 2H, J ) 7.4 Hz), 2.44 (m, 1H,
J ) 12.2 Hz and 2.2 Hz), 3.38 (dd, 1H, J ) 10.5 Hz and 7.6
Hz), 3.64 (dd, 1H, J ) 10.3 Hz and 3.7 Hz), 3.82 (m, 2H, J )
5.6 Hz), 4.54 (AB quartet, 2H), 6.2 (bs, 1H, D2O exch), 6.81
(m, 2H), 7.55, (m, 1H), 7.78 (s, 1H), 8.09 (s, 1H); 13C NMR (75
4
) 4 Hz), 118.43, 125.05 (2J H,F ) 14 Hz, J H,F ) 4 Hz), 130.75
3
1
(dd, J H,F ) 9 Hz and 6 Hz), 141.37, 159.88 (dd, J H,F ) 248
Hz, 3J H,F ) 10 Hz), 162.27 (dd, 1J H,F ) 249 Hz, 3J H,F ) 12 Hz),
174.34.); MS (CI + CH4)(m/z): 299 (M + 1)(2%), 281 (58), 211
(44), 193 (100), 167 (17). Anal. Calcd for C16H20F2O3: C, 64.42;
H, 6.76; F, 12.74. Found: C, 64.47; H, 7.07; F, 12.73.
3
MHz, CDCl3) δ 13.67, 18.31, 35.98, 36.36, 37.70 (d, J C,F ) 4
4
4
Hz), 58.32 (d, J C,F ) 4 Hz), 63.39, 65.20, 74.65 (d, J C,F ) 5
(2S)-2-[2′-(2′′,4′′Diflu or op h en yl)-2′-p r open yl]-1-a cetoxy-
3-h yd r oxyp r op a n e ((S)-14b). A mixture of diol 13a (5.01
g, 21.95 mmol) and Novo SP435 (0.26 g) in tank car grade
MeCN (25 mL) was cooled in an ice bath for 15 min. Added
vinyl acetate (4.0 mL, 43.4 mmol) and stirred at 0 °C for 6 h.
The reaction mixture was filtered, the beads were washed with
EtOAc (30 mL), and the combined organics were evaporated
(<30 °C). The residue was purified by column chromatogra-
phy, eluting with 10-50% EtOAc/hexanes. Pooling the rel-
evant fractions yielded the monoacetate (S)-14b (4.23 g, 71.3%;
2
2
4
Hz), 104.23 (t, J C,F ) 26 Hz), 111.58 (dd, J C,F ) 21 Hz, J C,F
2
4
) 3 Hz), 124.95 (dd, J C,F ) 13 Hz, J C,F ) 4 Hz), 130.46 (dd,
3J C,F ) 6 Hz and 9 Hz), 144.32, 150.85, 158.59 (dd, 1J C,F ) 247
3
1
3
Hz, J C,F ) 12 Hz), 162.72 (dd, J C,F ) 250 Hz, J C,F ) 12 Hz),
173.62; MS(FAB)(m/z) 454 (DiOBu, M + 1)(7%), 384 (M +
1)(100%), 366 (17), 296 (9), 224 (6), 213 (5). Anal. Calcd for
C18H23F2N3O4: C, 56.39; H, 6.05; N, 10.96. Found: C, 56.42;
H, 6.60; N, 10.63.
(2R)-2-[2′-(2′′,4′′-Diflu or oph en yl)-2′-pr open yl]-1-acetoxy-
3-h yd r oxyp r op a n e ((R)-14b). Lipase CE (2.0 g) was added
to a solution of diol 13a (10.0 g, 43.8 mmol) and vinyl acetate
(8.0 mL, 86.8 mmol) in HPLC grade toluene (200 mL). The
mixture was stirred at room temperature with periodic HPLC
monitoring. After 26 h the reaction mixture was filtered
through a Celite pad which was washed with tBME (20 mL).
The filtrate was evaporated (<30 °C) and purified by column
chromatography, eluting with 10-35% EtOAc/hexane. Pooling
the relevant fractions yielded the diacetate 13b (0.66 g), a
mixture of mono- and diacetate (0.89 g), and pure monoacetate
ee 0.982): [R]23 ) -13.9° (c, 1.688, EtOH); IR (neat on KBr):
D
3453 (b), 3082, 2949, 2899, 1738 (CdO), 1618, 1502, 1246,
1140, 1085, 1040, 970, 851, 610 cm-1 1H NMR (300 MHz,
;
CDCl3): δ 1.80 (m, 1H), 2.04 (s, 3H), 2.54 (m, 3H; D2O exch
sept, 2H), 3.48 (dd, 1H, J ) 11.2 Hz and 6.1 Hz), 3.55 (dd, 1H,
J ) 11.2 Hz and 4.6 Hz), 4.07 (dd, 1H, J ) 11.2 Hz and 6.3
Hz), 4.13 (1H, J ) 11.2 Hz and 4.7 Hz), 5.21 (s, 1H), 5.28 (s,
4
1H), 6.77-6.88 (m, 2H), 7.24 (dt, 1H, J H,F ) 8.4 Hz and J H,H
4
) 6.4 Hz); 13C NMR (75 MHz, CDCl3): δ 20.84, 35.07 (d, J H,F
3
) 3 Hz), 38.66, 61.99, 63.96, 104.20 (t, J C,F ) 26 Hz), 111.35
(R)-14b as a viscous oil (10.37 g, 87.6%; ee 0.970): [R]24
)
D
2
4
2
(dd, J C,F ) 21 Hz, J C,F ) 3 Hz), 118.42, 125.08 (dd, J H,F
)
+13.9° (c, 1.085, EtOH); IR (neat on KBr): 3446 (b), 3082,
2951, 1737 (CdO), 1619, 1502, 1257, 1140, 1085, 1040, 970,
14 Hz, 4J H,F ) 3 Hz), 130.78 (dd, 3J C,F ) 6 Hz and 9 Hz), 141.39,
159.90 (dd, 1J C,F ) 253 Hz, J C,F ) 15 Hz), 162. 19 (dd, 1J C,F
)
3
1
851, 610 cm-1; H NMR (300 MHz, CDCl3): δ 1.81 (m, 1H),
3
249 Hz, J C,F ) 12 Hz), 171.74; MS (CI + CH4)(m/z): 271 (M
+ 1)(2%), 253 (16), 211 (41), 193 (100), 167 (22). Anal. Calcd
for C14H16F2O3: C, 62.21; H, 5.97; F, 14.06. Found: C, 61.95;
H, 6.31; F, 13.87.
1.95 (bs, 1H), 2.06 (s, 3H), 2.54 (sept, 2H), 3.50 (dd, 1H, J )
11.3 Hz and 6.2 Hz), 3.57 (dd, 1H, J ) 11.3 Hz and 4.5 Hz),
4.07 (dd, 1H, J ) 11.3 Hz and 6.4 Hz), 4.17 (1H, J ) 11.3 Hz
and 4.5 Hz), 5.22 (s, 1H), 5.28 (d, 1H, J ) 1.2 Hz), 6.77-6.88
4
(m, 2H), 7.24 (dt, 1H, J H,F ) 8.5 Hz and J H,H ) 6.5 Hz); 13C
NMR (75 MHz, CDCl3): δ 20.88, 35.04 (d, 4J H,F ) 3 Hz), 38.68,
Su p p or t in g In for m a t ion Ava ila b le: 1H and 13C NMR
spectra of compounds (R,R)-9, (R,S)-9, (R)-10, (R)-11b, (R,S)-
12b, (R)-14b, (S)-14c and (S)-14b, and 1H NMR spectra for
the borate ester of 13a (12 pages). This material is contained
in libraries on microfiche, immediately follows this article in
the microfilm version of the journal, and can be ordered from
the ACS; see any current masthead page for ordering
information.
3
2
62.10, 63.89, 104.23 (t, J C,F ) 26 Hz), 111.36 (dd, J C,F ) 21
Hz, 4J C,F ) 3 Hz), 118.48, 125.06, 130.71 (dd, 3J C,F ) 6 Hz and
9Hz), 141.33, 159.87 (dd, J C,F ) 237 Hz, J C,F ) 11 Hz), 162.
28 (dd, J C,F ) 237 Hz, J C,F ) 11 Hz), 171.68; MS (CI +
CH4)(m/z): 271 (M + 1)(7%), 253 (22), 211 (32), 193 (100), 167
(14). Anal. Calcd for C14H16F2O3: C, 62.21; H, 5.97; F, 14.06.
Found: C, 62.02; H, 5.85; F, 13.96.
1
3
1
3
(2S)-2-[2′-(2′′,4′′-Diflu or op h en yl)-2′-p r op en yl]-1-b u t y-
r oxy-3-h yd r oxyp r op a n e ((S)-14c). A mixture of dibutyrate
J O9709920