Chemoenzymatic Synthesis of All Four Stereoisomers of Sphingosine from Chlorobenzene: Glycosphingolipid Precursors

Article abstract of DOI:10.1021/jo971335a

Advantageous use of homochiral cyclohexadiene-cis-1,2-diol 2, available by means of biocatalytic oxidation of chlorobenzene with toluene dioxygenase, has enabled the synthesis of all four enantiomerically pure C₁₈-sphingosines 1. The four requisite diastereomers of azido alcohols 4a-d were accessed by regioselective opening of epoxides 7 and 8 with either azide or halide ions. The configuration of C4 and C5 in azides 4 defines the stereochemistry of the incipient sphingosine chain, liberated from 4 by the oxidative cleavage of the C1-C6 olefin. For L-thereo-sphingosine (1b), lactol 20b generated by this cleavage was converted by periodate oxidation to azido deoxy L-threose 22b, which gave 1b upon Wittig olefination and reduction. Similarly, D-erythrosphingosine (1a) and L-erythro-sphingosine (1c) were generated from 4a,c, respectively. The last sphingosine (Id) was synthesized from the silyl-protected azido alcohol 29d. Subsequent transformations provided silyl-protected azido deoxy D-threose 32d, which upon Wittig olefmation and reduction gave D-threo-sphingosine (1d). Experimental and spectral data are provided for all new compounds.

Full text of DOI:10.1021/jo971335a

510
J . Org. Chem. 1998, 63, 510-520
Ch em oen zym a tic Syn th esis of All F ou r Ster eoisom er s of
Sp h in gosin e fr om Ch lor oben zen e: Glycosp h in golip id P r ecu r sor s1a
Thomas C. Nugent† and Tomas Hudlicky*
Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200
Received J uly 22, 1997
Advantageous use of homochiral cyclohexadiene-cis-1,2-diol 2, available by means of biocatalytic
oxidation of chlorobenzene with toluene dioxygenase, has enabled the synthesis of all four
enantiomerically pure C18-sphingosines 1. The four requisite diastereomers of azido alcohols 4a -d
were accessed by regioselective opening of epoxides 7 and 8 with either azide or halide ions. The
configuration of C4 and C5 in azides 4 defines the stereochemistry of the incipient sphingosine
chain, liberated from 4 by the oxidative cleavage of the C1-C6 olefin. For L-threo-sphingosine
(1b), lactol 20b generated by this cleavage was converted by periodate oxidation to azido deoxy
L-threose 22b, which gave 1b upon Wittig olefination and reduction. Similarly, D-erythro-
sphingosine (1a ) and L-erythro-sphingosine (1c) were generated from 4a ,c, respectively. The last
sphingosine (1d ) was synthesized from the silyl-protected azido alcohol 29d . Subsequent
transformations provided silyl-protected azido deoxy D-threose 32d , which upon Wittig olefination
and reduction gave D-threo-sphingosine (1d ). Experimental and spectral data are provided for all
new compounds.
Ch a r t 1. F ou r Ster eoisom er s of C18-Sp h in gosin e
In tr od u ction
Syn th esized fr om Ar en e-cis-d iol 2
Sphingosines constitute a group of related long-chain
aliphatic 2-amino-1,3-diols, of which 2-amino-D-erythro-
4(E)-octadecene-1,3-diol (1a ) (Chart 1) occurs most fre-
quently in animal glycosphingolipids.2 Sphingosines are
known inhibitors of protein kinase C and are the back-
bone of glycosphingolipids. This larger family of biomol-
ecules is involved in a plethora of processes related to
cell growth, differentiation, adhesion, and neuronal
repair.3 Glycosphingolipids contain two basic structural
motifs: carbohydrate and ceramide. The ceramide por-
tion consists of a sphingoid base and an amide-linked
fatty acyl chain, e.g., stearoyl (Chart 2) or palmitoyl. The
structural variation in fatty acids (N-acyl portion), sph-
ingosines, and carbohydrates results in a great variety
of chemically distinct glycosphingolipids.2
Glycosphingolipids are found in the cell membrane of
all animal and many plant cells, where they serve as
identifying markers and regulate cellular recognition,
growth, and development.4a They are thought to function
by anchoring the hydrophobic ceramide portion (Chart
2) in the plasma membrane, exposing the hydrophilic
carbohydrate portion to the surrounding exterior which
specifies the intended biological function.4b Among their
biological functions are (1) HIV binding to galactosyl
ceramide receptor sites in cells lacking the principal CD4
cellular receptor,5 (2) an unambiguous link between
specific sphingolipids and malignant tumors which en-
ables them to be used as 'biological markers' for possible
early detection of cancer,4a and (3) potent and reversible
inhibition of protein kinase C6 by breakdown products
of glycosphingolipids, e.g., sphingosine, sphinganine, and
lysosphingolipids (Chart 2). The latter is particularly
significant because protein kinase C mediates cellular
responses for tumor promoters, hormones, and growth
factors.7 The ongoing recognition of glycosphingolipids
as fundamental mediators of cellular interactions con-
tinues to sustain research in this field.
† Current address: Department of Chemistry, University of Arizona,
Tucson, AZ 85721.
(1) Preliminary results of this work have been published; see: (a)
Hudlicky, T.; Nugent, T. C.; Griffith, W. J . Org. Chem. 1994, 59, 7944.
(b) Banwell, M. G.; Haddad, N.; Hudlicky, T.; Nugent, T. C.; Mackay,
M. F.; Richards, S. L. J . Chem. Soc., Perkin Trans. 1 1997, 1779.
(2) Hakomori, S. Sphingolipid Biochemistry. In Handbook of Lipid
Research; Kanfer, J . N., Hakomori, S., Eds.; Plenum: New York, 1983;
Vol. 3, p 1.
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G.; Coso, O. A.; Gutkind, J . S.; Spiegel, S. Nature 1996, 381, 800. (f)
Inooka, S.; Toyokuni, T. Biochem. Biophys. Res. Commun. 1996, 218,
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(5) Harouse, J . M.; Bhat, S.; Spitalnik, S. L.; Laughlin, M.; Stefano,
K.; Silberberg, D. H.; Gonzalez-Scarano, F. Science 1991, 253, 320.
(6) Hannun, Y. A.; Bell, R. M. Science 1989, 243, 500.
(7) Merrill, A. H.; Nimkar, S.; Menaldino, D.; Hannun, Y. A.; Loomis,
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R.; Liotta, D. C. Biochemistry 1989, 28, 3138.
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Schmidt, R. R. Pure Appl. Chem. 1989, 61, 1257.
S0022-3263(97)01335-2 CCC: $15.00 © 1998 American Chemical Society
Published on Web 01/16/1998

Stereoisomers of Sphingosine from Chlorobenzene
J . Org. Chem., Vol. 63, No. 3, 1998 511
Ch a r t 2. Gen er ic Str u ctu r e of a Glycosp h in golip id
Ch a r t 3. Retr osyn th etic An a lysis of Sp h in gosin e
of L-serine derivatives and carbohydrates have culmi-
nated in highly efficient and diastereoselective syntheses
of D-erythro-sphingosine (1a ), the naturally occurring
stereoisomer, and L-threo-sphingosine (1b). The most
noteworthy to date is Polt’s9h synthesis of L-threo-sphin-
gosine10 in five steps and in 60% overall yield from
L-serine.
A survey of the remaining sphingosine literature1a,11
reveals some of the more novel and efficient syntheses
of D-erythro-sphingosine (1a ), as well as the first synthe-
sis by Shapiro and Segal in 1954.11a,b In 1983 Vasella
employed the Katsuki-Sharpless asymmetric epoxida-
tion to set the chirality of an enynol which ultimately
led to a six-step synthesis of D-erythro-sphingosine (1a )
in 50% overall yield.11c,d Among the other syntheses
Of the four sphingosines, only one (D-erythro-sphin-
gosine) is commercially available. We therefore envi-
sioned a general synthetic plan that would rely on the
functionalization of cis-diol 2 (Chart 1) at C4-C5 in such
a way as to define the two chiral centers in sphingosines
for all four stereoisomers. The introduction of azide and
hydroxyl functionalities at C4-C5 of acetonide 3 would
lead to azido alcohols 4. Subsequently, the C1-C6 olefin
of 4 would be oxidatively cleaved to 5, followed by further
oxidative cleavage of the C2-C3 diol to liberate the key
synthon, azido deoxy threose or erythrose, 6 (Chart 3).
In this fashion, the two stereocenters in sphingosines
could be independently set prior to the double oxidative
cleavage that provides the terminal alcohol as well as
the aldehyde functionality required for the Wittig chain
extension. In this article we report the synthesis of all
four isomers by this strategy.
(9) Syntheses of sphingosine from L-serine: (a) Newman, H. J . Am.
Chem. Soc. 1973, 95, 4098. (b) Tkaczuk, P.; Thornton, E. R. J . Org.
Chem. 1981, 46, 4393. (c) Boutin, R. H.; Rapoport, H. J . Org. Chem.
1986, 51, 5320. (d) Herold, P. Helv. Chim. Acta 1988, 71, 354. (e)
Nimkar, S.; Menaldino, D.; Merrill, A. H.; Liotta, D. Tetrahedron Lett.
1988, 29, 3037. (f) Garner, P.; Park, J . M.; Malecki, E. J . Org. Chem.
1988, 53, 4395. (g) Dondoni, A.; Fantin, G.; Fogagnolo, M.; Pedrini,
P. J . Org. Chem. 1990, 55, 1439. (h) Polt, R.; Peterson, M. A.; DeYoung,
L. J . Org. Chem. 1992, 57, 5469.
(10) Whereas all organic chemists seem to agree that D-erythro- and
L-erythro-sphingosine have structures 1a ,c, respectively (Chart 1), the
naming of the threo enantiomers lacks consistency. In general,
carbohydrate chemists have adopted L-threo-sphingosine as 1b, while
non-carbohydrate chemists tend to refer to it as D-threo-sphingosine.
For the reasons outlined below, we believe the L-threo assignment of
1b is correct and that the D-threo descriptor should be discontinued
for the assignment of sphingosine 1b. The assignment of natural
sphingosine (1a ) is based on a Fischer projection in which the primary
alcohol of 1a is placed at the top of the projection.9a Once this reference
point has been established, comparison of the Fischer projections of
D-erythrose and sphingosine clearly shows their analogous spatial
arrangement. This fact alone determines whether two vicinal chiral
centers are described as erythro or threo, n ot their stereochemical R
or S assignment; i.e., D-erythrose has the 2R,3R configuration, and
D-erythro-sphingosine (1a ) has the 2S,3R configuration, but it is
irrelevant. When sphingosine 1b is depicted in a Fischer projection,
it resembles L-threose and not D-threose.
Resu lts a n d Discu ssion
Many syntheses of enantiomerically pure sphingosines
have relied on the use of carbohydrates or L-serine as
chiral building blocks. The first such application was
reported by Reist8a in 1970 using 3-amino-3-deoxy-1,2:
5,6-diisopropylidene-R-D-allofuranose, which was followed
3 years later by Newman’s9a synthesis of sphingosine
from L-serine. Since then exhaustive studies on the use
(8) Syntheses of sphingosine from carbohydrates: (a) Reist, E. J .;
Christie, P. H. J . Org. Chem. 1970, 35, 4127. (b) Obayashi, M.;
Schlosser, M. Chem. Lett. 1985, 1715. (c) Schmidt, R. R.; Zimmermann,
P. Angew. Chem., Int. Ed. Engl. 1986, 25, 725. (d) Schmidt, R. R.;
Zimmermann, P. Tetrahedron Lett. 1986, 27, 481. (e) Kiso, M.;
Nakamura, A.; Tomita, Y.; Hasegawa, A. Carbohydr. Res. 1986, 158,
101. (f) Kiso, M.; Nakamura, A.; Nakamura, J .; Tomita, Y.; Hasegawa,
A. J . Carbohydr. Chem. 1986, 5 (2), 335. (g) Koike, K.; Numata, M.;
Sugimoto, M.; Nakahara, Y.; Ogawa, T. Carbohydr. Chem. 1986, 158,
113. (h) Zimmermann, P.; Schmidt, R. R. Liebigs Ann. Chem. 1988,
663. (i) Sugawara, T.; Norisada, M. Carbohydr. Res. 1989, 194, 125.
(j) Yadav, J . S.; Vidyanand, D.; Rajagopal, D. Tetrahedron Lett. 1993,
34, 1191. (k) Murakami, T.; Minamikawa, H.; Hato, M. Tetrahedron
Lett. 1994, 35, 745. (l) Schmidt, R. R.; Wild, B. Tetrahedron: Asym-
metry 1994, 5, 2195. (m) Li, Y. L.; Sun, X. L.; Wu, Y. L. Tetrahedron
1994, 50, 10727. (n) Schmidt, R. R.; Ba¨r, T.; Wild, B. Synthesis 1995,
869. (o) Murakami, T.; Hato, M. J . Chem. Soc., Perkin Trans. 1 1996,
823. (p) Shinozaki, K.; Mizuno, K.; Masaki, Y. Chem. Pharm. Bull.
1996, 44, 927. (q) Synthesis from D-isoascorbic acid: Tuch, A.; Sanie`re,
M.; Merrer, Y. L.; Depezay, J . C. Tetrahedron: Asymmetry 1996, 7,
897.
(11) Miscellaneous approaches to sphingosines: (a) Shapiro, D.;
Segal, K. H. J . Am. Chem. Soc. 1954, 76, 5894. (b) Shapirio, D.; Segal,
K. H.; Flowers, H. M. J . Am. Chem. Soc. 1958, 80, 1194. (c) Bernet,
B.; Vasella, A. Tetrahedron Lett. 1983, 24, 5491. (d) J ulina, R.; Herzig,
T.; Bernet, B.; Vasella, A. Helv. Chim. Acta 1985, 69, 368. (e) Cardillo,
G.; Orena, M.; Sandri, S.; Tomasini, C. Tetrahedron 1986, 42, 917. (f)
Findeis, M. A.; Whitesides, G. M. J . Org. Chem. 1987, 52, 2838. (g)
Nicolaou, K. C.; Caufield, T.; Kataoka, H.; Kumazawa, T. J . Am. Chem.
Soc. 1988, 110, 7910. (h) Shibuya, H.; Kawashima, K.; Ikeda, M.;
Kitagawa, I. Tetrahedron Lett. 1989, 30, 7205. (i) Takano, S.; Iwabu-
chi, Y.; Ogasawara, K. J . Chem. Soc., Chem. Commun. 1991, 820. (j)
Somfai, P.; Olsson, R. Tetrahedron 1993, 49, 6645. (k) Solladie´-Cavallo,
A.; Koessler, J . L. J . Org. Chem. 1994, 59, 3240. (l) Enders, D.;
Whitehouse, D. L.; Runsink, J . Chem. Eur. J . 1995, 1, 382. (m) Davis,
F. A.; Reddy, G. V. Tetrahedron Lett. 1996, 37, 4349 and references
cited therein.

512 J . Org. Chem., Vol. 63, No. 3, 1998
Nugent and Hudlicky
Sch em e 1a
a
Reagents and conditions: (i) 2,2-dimethoxypropane, cat. p-TsOH, CH2Cl2; (ii) NBS, DME/H2O (3:2), 0 °C; (iii) NaOH (1.1 equiv),
Bu4HNSO4 (1.0 equiv), CH2Cl2 reflux; (iv) m-CPBA, CH2Cl2; (v) NaN3, NH4Cl, DME/EtOH/H2O (3:3:2), 65 °C; (vi) LiCl (5.0 equiv), ethyl
acetoacetate (3.0 equiv), THF, 45 °C; (vii) LiBr (1.1 equiv), ethyl acetoacetate (2.0 equiv), THF, 35 °C; (viii) NaN3 (3.0 equiv), DMF; (ix)
NaN3 (15 equiv), DMSO; (x) NaN3 (3.0 equiv), DMSO, 70 °C.
those by Nicolaou11g and Solladie´11k are noteworthy for
their brevity and elegance.
sioned the synthesis of all four stereoisomers of sphin-
gosine from 3 (Chart 3). The two stereocenters of the
title compounds would be established early, by means of
a cyclic rather than acyclic intermediate, when a high
degree of regio- and stereochemical control would still
be possible.
Ch em o- a n d Ster eoselective F u n ction a liza tion of
th e C4-C5 Olefin . cis-Diol 2 was protected as its
acetonide 315 and converted to epoxide 712j or 81a as
desired (Scheme 1). Conversely exposure of 3 to N-
bromosuccinimide (NBS), in the presence of H2O, led
predominantly to bromohydrin 9 in 30% yield. The minor
diastereoisomer 10 was produced in 3% yield. The
regiochemistry of bromohydrins 9 and 10 was confirmed
by 1H NMR irradiation studies and their stereochemistry
by conversion to epoxides 8 and 7, respectively.
In recent years the use of enantiomerically pure
cyclohexadiene-cis-1,2-diols in the total synthesis of
carbohydrates, cyclitols, and oxygenated alkaloids has
increased dramatically.12,13 To further demonstrate the
general utility of these dienediols, obtained by enzymatic
oxidation of chlorobenzene with toluene dioxygenase from
the whole cells of Pseudomonas putida 39D,14 we envi-
(12) For recent examples of arenediols in synthesis, see: (a)
Hudlicky, T.; Seoane, G.; Pettus, T. J . Org. Chem. 1989, 54, 4239. (b)
Hudlicky, T.; Luna, H.; Price, J . D.; Rulin, F. J . Org. Chem. 1990, 55,
4683. (c) Downing, W.; Latouche, R.; Pitoll, C. A.; Pryce, R. J .; Roberts,
S. M.; Ryback, G.; Williams, J . O. J . Chem. Soc., Perkin Trans. 1 1990,
2613. (d) Ley, S. V.; Redgrave, A. J .; Taylor, S. C.; Ahmed, S.; Ribbons,
D. W. Synlett 1991, 741. (e) Boyd, D. R.; Dority, M. R. J .; Hand, M.
V.; Malone, J . F.; Sharma, N. D.; Dalton, H.; Gray, D. J .; Sheldrake,
G. N. J . Am. Chem. Soc. 1991, 113, 666. (f) Carless, H. A. J .
Tetrahedron Lett. 1992, 6379. (g) Banwell, M. G.; Corbett, M.; Mackay,
M. F.; Richards, S. L. J . Chem. Soc., Perkin Trans. 1 1992, 1. (h)
Hudlicky, T.; Mandel, M.; Kwart, L. D.; Whited, G. M. J . Org. Chem.
1993, 58, 2331. (i) Hudlicky, T.; Rouden, J .; Luna, H. J . Org. Chem.
1993, 58, 985. (j) Hudlicky, T.; Rouden, J .; Luna, H.; Allen, S. J . Am.
Chem. Soc. 1994, 116, 5099. (k) Hudlicky, T.; Tian, X.; Ko¨nigsberger,
K.; Maurya, R.; Rouden J .; Fan, B. J . Am. Chem. Soc. 1996, 118, 10752.
(l) Gonzalez, D.; Schapiro, V.; Seoane, G.; Hudlicky, T. Tetrahedron:
Asymmetry 1997, 8, 975.
(13) For comprehensive reviews of cyclohexadiene-cis-diol chemistry,
see: (a) Widdowson, D. A.; Ribbons, D. W.; Thomas, S. D. J ansen Chim.
Acta 1990, 8, 3. (b) Carless, H. A. J . Tetrahedron: Asymmetry 1992,
3, 795. (c) Brown, S. M.; Hudlicky, T. In Organic Synthesis: Theory
and Practice; Hudlicky, T., Ed.; J AI Press: Greenwich, CT, 1993; Vol.
2, p 113. (d) Hudlicky, T.; Reed, J . W. In Advances in Asymmetric
Synthesis; Hassner, A., Ed.; J AI Press: Greenwich, CT, 1994; Vol. 1,
p 271. (e) Grund, A. D. SIM NEWS 1995, 45, 59. (f) Hudlicky, T.;
Thorpe, A. J . J . Chem. Soc., Chem. Commun. 1996, 1993. (g) Hudlicky,
T. Chem. Rev. 1996, 96, 3. (h) Hudlicky, T.; Entwistle, D. A.; Pitzer,
K. K.; Thorpe, A. J . Chem. Rev. 1996, 96, 1195. (i) Hudlicky, T. In
Green Chemistry: Designing Chemistry for the Environment; Anastas,
P. T., Williamson, T., Eds.; ACS Symposium Series 626; American
Chemical Society: Washington, DC, 1996; Chapter 14.
trans-Azido alcohols 4b,1b d 1a were directly accessible,
in high yield, from epoxides 7 and 8, respectively, upon
exposure to NaN3 (Scheme 1). The synthesis of the two
(14) (a) Commercially available from Genencor International, Inc.,
Palo Alto, CA. (b) Gibson, D. T.; Kock, J . R.; Kallio, R. E. Biochemistry
1968, 7, 2653. (c) Gibson, D. T.; Koch, J . R.; Schuld, C. L.; Kallio, R.
E. Biochemistry 1968, 7, 3795. (d) Gibson, D. T.; Hensley, M.;
Yoshioka, H.; Mabry, J . J . Biochemistry 1970, 9, 1626. (e) Gibson, D.
T. Crit. Rev. Microbiol. 1971, 1, 199. (f) Gibson, D. T. Tox. Environ.
Chem. 1982, 5, 237. (g) Gibson, D. T.; Subramanian, V. In Microbial
Degradation of Organic Compounds; Gibson, D. T., Ed.; Microbiology
Series 13; Marcel Dekker: New York, 1984; Chapter 7. (h) Gibson,
D. T.; Zylstra, G. J .; Chauhan, S. In Pseudomonas: Biotransformations,
Pathenogenesis and Evolving Biotechnology; Silver, S., Ed.; American
Society for Microbiology: Washington, DC, 1990; Chapter 13, p 121.
(i) Zylstra, G. J .; Gibson, D. T. In Genetic Engineering; Setlow, J . A.,
Ed.; Pergamon: New York, 1991; Vol. 13, p 183.
(15) (a) Hudlicky, T.; Price, J . D.; Rulin, F.; Tsunoda, T. J . Am.
Chem. Soc. 1990, 112, 9439. (b) Hudlicky, T.; Luna, H.; Price, J . D.;
Rulin, F. Tetrahedron Lett. 1989, 30, 4053. (c) Hudlicky, T.; Price, J .
D. Synlett 1990, 159.

Stereoisomers of Sphingosine from Chlorobenzene
J . Org. Chem., Vol. 63, No. 3, 1998 513
Sch em e 2a
Ta ble 1. Con tr ol of Ha logen Disp la cem en t
molarity
yield (%)
ratiob of
entry SMa SM NaN3 NaN3/SM solvent T (°C)c 4a 4d
1
2
3
4
13 0.18 0.70
12 0.20 0.80
13 0.19 5.70
12 0.61 9.70
3.9
4.0
30.0
16.0
DMF
DMF
DMSO
DMSO
85
13 77
14 76
90
40d
40d
0
0
75 22
a
b
SM, starting material (halohydrin). Molar ratio of sodium
azide to halohydrin. c Temperature at which noticeable consump-
tion of halohydrin began. An ultrasound sonicator was used to
d
maintain homogeneity; the temperature of the bath was a constant
40 °C.
remaining azido alcohols (4a ,c) presented a greater
challenge. Earlier we reported12j the synthesis of cis-
azido alcohol 4c from chlorohydrin 1116 in 91% yield. In
a similar manner epoxide 8 was treated with LiBr to give
bromohydrin 12, which gave 4a upon exposure to a large
excess of NaN3.
a
Reagents and conditions: (i) O3 (excess), MeOH, -78 °C; (ii)
NaBH3CN, pH ∼3.0, 0 °C; (iii) NaBH4, -30 °C or rt; (iv) NaBH4,
MeOH, 0 °C; (v) NaBH4, MeOH, rt; (vi) Amberlyst 15 (wet) ion-
exchange resin, strongly acidic in MeOH/H2O.
Initial attempts to synthesize 4a were unsuccessful.
When chlorohydrin 13 was subjected to the same reaction
conditions as those for the production of 4c (from 11),
the epimeric azido alcohol 4d was formed as the major
product (Table 1, entry 1). It was only in the presence
of a large excess of NaN3 that 4a was formed. Thus by
varying the amount of NaN3, bromohydrin 12 could be
selectively converted to either 4a or 4d . This unique
stereochemical outcome is understandable if one consid-
ers the two competing chemical processes. The first is
the SN2 displacement of halide by the azide; the second
is the reconstitution of epoxide 8, followed by its in situ
opening with azide. The data (Table 1) clearly suggest
that the former process prevails at high molar ratios of
NaN3 to halohydrin, while the latter predominates at low
molar ratios.
Interestingly 4d was synthesized directly when bro-
mohydrin 9 was treated with NaN3 in DMSO at 70 °C
(Scheme 1).17 The spectral data for the two indepen-
dently synthesized azido alcohols 4d were indistinguish-
able. Since the formation of 4d from 9 must proceed via
epoxide 8, we also attempted the conversion of 9 to 12
with NaBr, expecting the intermediate epoxide to open
regioselectively. Unfortunately, only decomposition was
observed at elevated temperatures.
tion. When another stereoisomer of sphingosine is
synthesized using stereoisomeric intermediates, it will
have the same number but a different letter. For
example, all compounds which could potentially lead to
the synthesis of D-erythro-sphingosine (1a ) will carry the
letter “a”.)
Syn th esis of L-th r eo-Sph in gosin e (1b) an d D-er yth -
r o-Sp h in gosin e (1a ). For L-threo-sphingosine (1b) azido
alcohol 4b was protected as its acetate 14b and subjected
to a variety of ozonolysis conditions (Scheme 2). Ester
aldehyde 15b and hydroxy ester 16b were isolated when
the ozonide derived from 14b was worked up under the
reducing conditions of NaBH4 and NaCNBH3, respec-
tively.18 Ester 16b, obtained in 82% yield, was converted
to the free diol 17b, with the expectation that the
protected azido deoxy threose 18b could be generated
(Scheme 2). Unfortunately a nonspecific migration of the
acetyl group in 17b occurred; after several different acidic
reaction conditions were examined, to no avail, this
approach was abandoned.19
Treatment of the ozonide derived from 14b with a large
excess of NaBH4, even at room temperature, failed to
With the access to the required azido alcohols 4a -d
assured, we turned our attention to the synthesis of all
four enantiomerically pure sphingosines. (Note: All
compounds leading to the synthesis of a particular
stereoisomer of sphingosine bear the same letter designa-
(18) Interestingly a vinyl azide was produced using the conditions
shown below. While most of the data were collected for the alcohol b
(1H NMR, 13C NMR, IR, MS), which was easier to handle (approximate
half-life at room temperature of 24 h), the 1H NMR of the aldehyde a
showed the elimination had already occurred. Only one geometric
isomer (not assigned) was observed. Reagents and conditions: (i) (1)
O3 (excess), NaHCO3 (5.5 equiv), MeOH, -78 °C, (2) NaBH4 (>10
equiv), CeCl3‚7H20, -20 °C; (ii) NaBH4 (excess), MeOH, rt.
(16) Chlorohydrin 11 (0.09 M), NaN3 (0.27 M), DMF, 12 h at 55 °C,
then 12 h at rt, 91% yield. (Note: The corresponding bromohydrin of
11 could not be synthesized without scrambling the stereochemistry
at the allylic site, i.e., a 1:1 mixture of epimeric products was observed.
T. Nugent and T. Hudlicky, unpublished results.)
(19) For neutral deprotection conditions using 0.5-1.0% I2 in MeOH
(w/v), see: Szarek, W. A.; Zamojski, A.; Tiwari, K. N.; Ison, E. R.
Tetrahedron Lett. 1986, 27, 3827. Unfortunately these neutral depro-
tection conditions were unknown to us when we were trying to
synthesize 17b.
(17) J . Rouden and T. Hudlicky, unpublished results.

514 J . Org. Chem., Vol. 63, No. 3, 1998
Ta ble 2. Wittig Olefin a tion of La ctol 22
Nugent and Hudlicky
lactol
ref
equiva
equiv of base
T (°C)
solvent
THF
THF/toluene
THF/toluene
DMSO
THF/toluene
THF
THF
% yield Z/E
22b
22b
22b
22b
22b
22b
22a
12b
4.0
1.2
1.2
4.0
2.0
3.2
3.2
4.0 n-BuLi
4.6 PhLi
5.5 PhLi
rt
-35
-78
rt
rt
rt
e
1/2
e
11j, 22ab
b
22b
23, 1a
8.0 dimsyl Nac
2.0 Na amylate
2.7 n-BuLi
2.7 n-BuLi
e
10/7
24/6d
14/4
rt
a
b
Equiv of salt, refers to equivalents of tetradecyltriphenylphosphonium bromide. Denotes modified Schlosser-Wittig conditions. c The
d
dimsyl anion was generated by the addition of 8.0 equiv of NaH to DMSO (the reaction solvent). Note this yield was not consistent;
subsequent reactions gave yields very similar to those of lactol 22a , i.e., combined yields (Z and E) of 20%. e Neither cis- nor trans-
azidosphingosine was observed.
Sch em e 3a
one-pot procedure, acid-catalyzed hydrolysis of acetonide
20b or 21b followed by NaIO4 cleavage provided in 65%
overall yield1a lactol 22b, the cyclic version of the key
sphingosine synthon 6, Chart 3. Note that the difference
in oxidation states is inconsequential as the carbonyl
atom is lost from both compounds during the periodate
cleavage.
Direct olefination of lactol 22b under optimized condi-
tions21 (Table 2) gave a chromatographically separable
mixture of cis- (23b) and trans-azidosphingosine (24b)
in 24% and 6% yield, respectively. The cis-azidosphin-
gosine (23b) was photoisomerized to trans-azidosphin-
gosine (24b) by means of a Hanovia 450-W lamp,24 Pyrex
filter,25,26 and diphenyl disulfide in a 4:1 mixture of
hexanes and dioxane.8g,11h Ultimately, the purified mix-
ture of cis-23b and trans-24b was photolyzed to give a
21% yield of trans-azidosphingosine (24b) from 22b.
Reduction8d,h of the azide was accomplished with H2S,
pyridine, and H2O to provide 1b whose peracetylation
(21) To ensure the integrity of our Wittig protocol, acetonide-
protected L-erythrose, available from cis-diol 2,12b was subjected to our
Wittig conditions.
a
Reagents and conditions: (i) O3 (excess), MeOH, -78 °C; (ii)
NaBH4, -30 °C to rt; (iii) NaBH3CN, pH ∼3.0, 0 °C; (iv) (1)
Amberlyst 15 (wet) ion-exchange resin, strongly acidic, H2O, (2)
NaIO4, H2O.
provide 19b or 20b directly. Only aldehyde 15b was
isolated. After workup, the crude aldehyde was reduced
with NaBH4. At 0 °C the seven-membered lactol 19b was
isolated in 55% yield, while at room temperature the five-
membered lactol 20b was obtained in 65% yield, because
of apparent cleavage of the acetate at the higher tem-
perature.20
We therefore turned to the ozonolysis of the unpro-
tected azido alcohol 4b (Scheme 3). To this end treat-
ment of 4b with ozone provided lactol 20b in 80% yield,
without the need of additional reduction. Alternatively,
when the ozonide derived from 4b was reduced with
sodium cyanoborohydride (NaBH3CN), lactone 21b was
observed, albeit in lower yield (60%). Fortuitously, in a
(22) (a) Schlosser, M.; Tuong, H. B.; Schaub, B. Tetrahedron Lett.
1985, 26, 311. (b) Bestmann, H. J .; Vostrowsky, O. In Topics in
Current Chemistry; Boschke, F. L., Ed.; Springer-Verlag: New York,
1983; Vol. 109, p 106.
(23) (a) Conia, J . M.; Limasset, J . C. Bull. Soc. Chem. Fr. 1967, 6,
1936. (b) Dauben, W. G.; Walker, D. M. J . Org. Chem. 1981, 46, 1103.
(c) Short, R. P.; Ranu, B. C.; Revol, J . M.; Hudlicky, T. J . Org. Chem.
1983, 48, 4453.
(24) In our initial communication detailing the synthesis of D-
erythro- and L-threo-sphingosine, we reported that a 400-W lamp was
used; however, all photoisomerizations were carried out with a 450-W
lamp.
(25) No special filter is needed, but Pyrex glassware is required.
We used a Pyrex round-bottomed flask for all photoisomerizations.
Pyrex filters out UV irradiation below 280 nm.26
(20) We believe that the lactols 19b and 20b are the products of
reduction of the corresponding lactonessfor precedent, see refs 12i,j.
(26) Moussebois, C.; Dale, J . J . Chem. Soc. C 1966, 260.

Stereoisomers of Sphingosine from Chlorobenzene
J . Org. Chem., Vol. 63, No. 3, 1998 515
Sch em e 4a
gave triacetyl-L-threo-sphingosine (25b), indistinguish-
1
able (vide H NMR spectrum and optical rotation) from
an authentic sample.27
Azido alcohol 4a , the precursor of naturally occurring
D-erythro-sphingosine (1a ), was subjected to the same set
of reactions as 4b to yield lactol 22a (Table 2) in 52%
overall yield. Under optimized Wittig olefination condi-
tions, outlined in Table 2, cis- (23a ) and trans-azidosph-
ingosine (24a ) were observed in 14% and 4% yield,
respectively. Photoisomerization resulted in a 12% yield
1
of trans-azidosphingosine 24a (from 22a ), displaying H
a
Reagents and conditions: (i) tetradecyltriphenylphosphonium
bromide, n-BuLi, THF; (ii) Ac2O, pyridine; (iii) K2CO3, MeOH; (iv)
PhSSPh, dioxane/hexane, Pyrex filter, Hanovia 450-W lamp.
NMR spectrum and optical rotation ([R]25D ) -34.2 (c 1.6,
CHCl3)) in agreement with the literature values ([R]20
D
) -32.9 (c 4.0, CHCl3)8h). The attainment of trans-
azidosphingosine (24a ), a known compound, constitutes
a formal synthesis of naturally occurring D-erythro-
sphingosine (1a ).1a
final product, we initiated the synthesis of L-erythro-
sphingosine (1c). Thus lactol 22c (Table 2) was synthe-
sized, in the same manner as 22b, and subsequently
treated with the Wittig ylide (prepared by addition of 4.5
equiv of n-BuLi in hexanes to 4.7 equiv of tetradecylt-
riphenylphosphonium bromide in THF at 0 °C f room
temperature). After 4 h, water (3.0 mL) was added, and
the reaction mixture was stirred for an additional 12 h.
This modification enables the hydrolysis of any imino-
phosphoranes or imines present and maximizes the
content of sphingosine 1c. Workup provided the crude
L-erythro-sphingosine (1c) product, as evidenced by TLC
analysis (Scheme 4).
Electr op h ilic Na tu r e of Azid es. 1. Syn th esis of
L-er yth r o-Sp h in gosin e (1c). It is known that alde-
hydes containing R-hydroxy groups are poor substrates
for Wittig olefination.9g This alone could account for the
poor yields we encountered. Although Wittig reactions
of lactols abound in the literature,22b no precedent was
found for successful olefination of lactols with the dispo-
sition of functionality and functional group type found
in 22b. In addition we failed to find an example in which
an azide moiety was present during a Wittig olefination
reaction. To explain the low yields ((E)- and (Z)-azi-
dosphingosines), we turned to the electrophilic nature of
azides in the presence of alkylidenephosphoranes. Ex-
amination of some of the alkylidenephosphorane
literature28a confirmed that azides are attacked by Wittig
reagents to form imines, nitrogen, and triphenylphos-
phine. Because triphenylphosphine is commonly used to
reduce azides to amines via hydrolysis of the intermedi-
ate iminophosphoranes,29 and because triphenylphos-
phine and octacos-14-ene (C28H56, alkylidenephosphorane
dimer) were isolated, as byproducts from the Wittig
reactions, the presence of imine and iminophosphorane
intermediates is highly probable.30 We reasoned that the
Wittig reaction could be improved if the reaction condi-
tions were adjusted to favor the final sphingosine product
by a one-pot Wittig olefination and triphenylphosphine-
mediated Staudinger reduction of azidosphingosine.
Expecting to improve the overall yield by channeling
both azido- and iminophosphoranyl sphingosines into the
A cursory analysis indeed indicated the yield of sph-
ingosine 1c was improved to 35-55%. Treatment of the
waxy material with excess Ac2O and pyridine provided
triacetates cis-26c and trans-25c in a 6:1 ratio, respec-
tively. The two geometric isomers proved inseparable by
chromatography and were therefore converted to the
corresponding acetamides cis-27c and trans-28c, which
proved to be as inseparable as the triacetates. Aceta-
mides cis-27c and trans-28c were synthesized in a
combined yield of 5% (this low isolated yield may reflect
the rather redundant and unsuccessful attempts at
purification) from 22c (Scheme 4) and were photoisomer-
ized and peracetylated as a mixture to provide triacetate
trans-25c, displaying optical rotation and an 1H NMR
spectrum in agreement with the literature.31 No further
attempt was made to optimize these conditions.
2. Syn th esis of th e F ou r th Ster eoisom er : D-th r eo-
Sp h in gosin e (1d ). A second-generation approach was
initiated in order to obviate some of the above problems.
Because of our earlier experience with the acetyl migra-
tion observed in 17b, we chose the tert-butyldiphenylsilyl
(TBDPS) protecting group. Azido alcohol 4d was pro-
tected as its tert-butyldiphenylsilyl ether 29d (85%) and
subsequently treated with ozone to provide methyl ester
30d (91%) (Scheme 5). Upon treatment with 1% I2 in
MeOH (w/v),19 30d provided the desired vicinal diol 31d
(80% yield).
(27) The sample was kindly provided by Professor Robin Polt of the
University of Arizona. (Note: In the Experimental Section of the Polt
paper, ref 9h, sphingosine 1b is referred to as the D-threo isomer; see
ref 10 for further clarification.)
(28) (a) Trippett, S. Chem. Soc. Rev. 1963, 17, 406. For a more
recent review on Wittig reactions, see: (b) Maryanoff, B. E.; Reitz, A.
B. Chem. Rev. 1989, 89, 863.
(29) (a) Pilard, S.; Vaultier, M. Tetrahedron Lett. 1984, 25, 1555.
(b) Falck, J . R.; Manna, S.; Viala, J .; Siddhanta, A. K.; Moustakis, C.
A.; Capdevila, J . Tetrahedron Lett. 1985, 26, 2287. (c) Lin, T. C.;
Cheng, M. C.; Peng, S. M.; Liu, S. T.; Kiang, F. M. J . Chin. Chem.
Soc. 1995, 42, 543.
(30) These products were not isolated until the synthesis of D-threo-
sphingosine (1d ). One possible reaction pathway for the formation of
octacosene and sphingosine is shown below.
In initial unoptimized reactions with Amberlyst 15
(wet) strongly acidic ion-exchange resin, the desired diol
31d was isolated in 44% yield. The remaining mass
(31) A 1:1 mixture of trans-triacetyl-L-erythro- (25c) and cis-triacetyl-
L-erythro-sphingosine (26c) was obtained after photoisomerization of
the 6:1 mixture of acetamides cis-27c and trans-28c, followed by
peracetylation. This 1:1 mixture of 25c and 26c had [R]27 ) +8.2 (c
D
0.9, CHCl3). Pure cis-triacetyl-L-erythro-sphingosine (26c) (obtained
by recrystallizing the original 6:1 mixture of cis- and trans-triacetates
twice from hexane) has [R]27 ) -4.4 (c 1.1, CHCl3), and pure trans-
D
triacetyl-L-erythro-sphingosine (25c) has [R]24 ) +12.1 (CHCl3).11h
D

516 J . Org. Chem., Vol. 63, No. 3, 1998
Nugent and Hudlicky
Sch em e 5a
type of deprotection (THF/H2O/CH3CO2H, THF/H2O/
CF3CO2H, or CH3OH/H2O/HCl) were employed.32
When vicinal diol 31d was treated with NaIO4, lactol
32d (75%) and its regioisomer 33d (13%) were formed.
Elaboration to the sphingosine skeleton was accom-
plished by coupling 32d with the appropriate phospho-
nium ylide, as delineated in Table 3. The best conditions
afforded a combined yield (13%) of cis- (23d ) and trans-
azidosphingosine (24d ) after Wittig olefination and TB-
DPS deprotection of cis-34 and trans-35. Note also the
isolation of some trans-2-hexadecene originating from the
base-induced decomposition of THF to acetaldehyde and
ethylene. Photoisomerization of cis-23d provided trans-
azidosphingosine (24d ), whose 1H NMR spectrum and
optical rotation ([R]25 ) -2.4 (c 0.27, CHCl3)) were in
D
agreement with the literature values.1a,11i
a
Reagents and conditions: (i) tert-butyldiphenylsilyl chloride
(2.0 equiv), imidazole (2.4 equiv), THF; (ii) (1) O3, MeOH, -78 °C,
(2) NaBH4 (excess), MeOH, 0 °C to rt; (iii) 1.0% I2 in MeOH, 45
°C; (iv) NaIO4 (2.0 equiv), MeOH/H2O, 3:1.
Con clu sion
The synthesis of all four sphingosine stereoisomers was
accomplished from a common precursor, cyclohexadiene-
cis-diol 2, in 8-10-step sequences. All of the steps in
these synthetic sequences proceeded in good to excellent
yield with the exception of the Wittig olefination. We
chose to pursue the olefinations with the azido deoxy
tetroses as intermediates because of the known lack of
nucleophilicity associated with sphingosines.3a In cou-
pling the sphingosine units to biologically desirable
electrophiles, the azido derivatives or the ceramide
derivatives enjoy more widespread use. Even though the
azido deoxy tetroses complicated the olefination protocols,
the advantage of generating four isomers from a single
source offsets this inconvenience. It is anticipated that
the third-generation refinements in these procedures will
address the Wittig step in more detail and will focus on
generating the ceramides by optimizing the Staudinger
component of the reaction and by maximizing the ace-
tylsphingosine content in the reaction mixtures before
the final purification. Other olefination alternatives,
especially those involving softer anions, will also be
examined in order to provide the useful azido analogues
of sphingosine. The primary goal of this effort, provision
of all four isomers from a simple intermediate, has been
achieved. We will report on further solutions to the
olefination protocol in due course.
balance consisted of three other compounds resulting
from migration of the tert-butyldiphenylsilyl group and/
or subsequent lactonization. These compounds were
isolated and fully identified (see the Experimental Sec-
tion, compounds 36-38).32 The ratio of these products
changed only slightly when literature conditions for this
(32) For the following conversion, we used the procedure described
in Leblanc, Y.; Fitzsimmons, B. J .; Adams, J .; Perez, F.; Rokach, J . J .
Org. Chem. 1993, 58, 832.
In our case, we observed three new compounds following the hydrolysis
of 30d . It seems that deprotection of the acetonide furnishes the
desired vicinal diol 31d first, followed by tert-butyldiphenylsilyl
migration to the adjacent alcohol moieties (based on TOCSY and
irradiation 1H NMR experiments of 37d and 38d ). When triol 36d
was stored neat or exposed to silica gel (short columns of silica gel
and fast elution are advised for purification), lactones 37d and 38d
slowly formed. Lactones 37d and 38d are stable, and each was fully
characterized. Suprisingly, when either pure lactone 37d or 38d was
dissolved in DMSO-d6, it immediately equilibrated to a 1:1 mixture of
the two lactones, as evidenced by 1H NMR. This ratio remained
unchanged even after 3 days. Silyl migration was not observed in
CDCl3 (1H NMR analysis).
Exp er im en ta l Section
Gen er a l Meth od s. All reactions were carried out in an
argon atmosphere with standard techniques for the exclusion
of air and moisture. Glassware used for moisture-sensitive
reactions was flame-dried under vacuum. All solvents were
reagent grade. Anhydrous solvents were dried immediately
before use. THF and toluene were distilled from sodium
benzophenone ketyl.
Dry oxygen containing about 2.5% ozone was introduced at
a speed of 4 L/min into a solution of substrate for the ozonolysis
experiments.
TLC plates were visualized by immersion in a vanillin stain
followed by warming on a hot plate. Flash chromatography
was carried out on Merck Kieselgel 60 silica gel (230-400
mesh). Impure products purified by column chromatography
were first impregnated onto silica gel.
1H NMR and APT 13C NMR spectra were recorded at 270
and 68 MHz. Proton and carbon chemical shifts are reported
in parts per million (ppm) relative to CDCl3 (1H NMR, 7.24
ppm; 13C NMR, 77.0 ppmsmiddle peak of the triplet). Alcohol
protons were identified by the addition of D2O. Elemental
In an attempt to thwart the silyl migration of triol 31d , we looked at
some nontraditional deprotection reagents. Thus when acetonide 30d
was treated with dimethylaluminum chloride,33 the results were very
encouraging (TLC), but upon workup, the four products were found
as usual. Finally, when 1% I2 in MeOH (w/v)19 was employed, at an
optimized temperature (45 °C), 31d was observed in an 80% yield.

Stereoisomers of Sphingosine from Chlorobenzene
J . Org. Chem., Vol. 63, No. 3, 1998 517
Ta ble 3. Wittig Olefin a tion Con d ition s for La ctol 32d
% yield
silanolb
equiv of salt
equiv of base
T (°C)
solvent
34d & 35d
dimera
trans-2-hexadecene
PPh3
2.2
1.8
1.8
3.5
2.2
3.0
3.5
4.0
4.4 PhLi
-50 to 0
THF
THF
THF
THF
0
9
c
c
20
19
c
≈5
20
c
57
43
47
not present
c
c
c
c
c
12
c
1.8 Na amylate
1.8 Na amylate
3.5 Na amylate
2.0 n-BuLi
2.7 n-BuLi
3.2 n-BuLi
rt
0 to rt
0 to rt
rt
4d
13d
0
≈19
12
THF
66
not present
not present
not present
not present
rt
THFe
toluene
THF
≈5
≈40
c
≈5
-78 to rt
rt
0f
c
3.6 n-BuLi
0g
c
c
a
b
d
The dimer refers to octacos-14-ene (C28H56). The silanol is tert-butyldiphenylsilanol. c Did not isolate. Percent yield determined by
treating the crude product 34d and 35d with n-Bu4NF and isolating the corresponding azidosphingosine. e The solvent was deoxygenated.
f 36% of the silyl-migrated product 33d and 35% of starting lactol isolated. TLC shows the silyl-migrated product 33d in <5 min; after
g
15 h neither starting lactol 32d nor 33d remains.
analyses were performed by Atlantic Microlab, Inc., and the
University of Florida.
min the reaction mixture was purged with N2 at -78 °C for
30 min. The solution was warmed to 0 °C, and methyl orange
indicator (e4 mg) was added. NaBH3CN (125 mg) was added,
and the red/pink solution color was maintained throughout
the reduction by the addition of 2.0 M aqueous HCl, as needed.
After 30 min, two more portions of NaBH3CN (125 mg, 30 min
apart) were added before warming to rt. Additional reductant
(270, 250, and finally 100 mg, 30-min intervals between
additions) was added at rt until TLC analysis showed only the
title compound. Acetone (5.0 mL) was then added to consume
the excess NaBH3CN. The reaction solution was reduced to
one-half of its original volume (rotary evaporator), and H2O
(40 mL) was added. The solution was extracted with EtOAc
(×3), and the combined organic extracts were dried (MgSO4)
and evaporated. Column chromatography (Hex/EtOAc, 3:1)
provided 16b (739 mg, 82% yield) as an oil: Rf ) 0.25 (hexanes/
EtOAc, 1:1); IR (neat) ν 3505, 2995, 2955, 2110, 2095, 1750
(3R,4S,5S,6S)-3-Azid o-1-ch lor o-5,6-O-isop r op ylid en e-1-
cycloh exen e-4,5,6-tr iol (4d ). NH4Cl (264 mg, 4.94 mmol,
4.00 equiv) and NaN3 (320 mg, 4.92 mmol, 4.00 equiv) were
added to a solution of epoxide 81a (250 mg, 1.23 mmol) in 1,2-
dimethoxyethane (13.0 mL), ethanol (10.0 mL), and H2O (8.0
mL). The resulting mixture was then heated at 60 °C. After
1 h the reaction mixture was cooled to rt, H2O (40.0 mL) was
added, and the solution was extracted with EtOAc (×3). The
combined organic extracts were dried (MgSO4) and evaporated.
Column chromatography using gradient elution (hexanes/
EtOAc, 3:1 f 2:1) afforded 4d (262.1 mg, 85%) as a clear oil.
Within 5 h at rt the oil became dark-brown, yet no decomposi-
tion was noticeable by 1H NMR. An analytical sample was
obtained after column chromatography (1% acetone in CH2Cl2
f 2% acetone in CH2Cl2): Rf ) 0.45 (hexanes/EtOAc, 2:1);
1
cm-1; H NMR (CDCl3) δ 5.17 (dd, J ) 2.7, 5.4 Hz, 1H), 4.78
[R]22 ) -120.1 (c 1.00, CHCl3); IR (neat) ν 3430, 2995, 2930,
D
2100, 1645 cm-1; 1H NMR (CDCl3) δ 5.81 (d, J ) 2.0 Hz, 1H),
4.57 (m, 2H), 4.27 (td, J ) 1.8, 8.6 Hz, 1H), 3.81 (dt, J ) 2.1,
8.1 Hz, 1H), 2.54 (d, J ) 7.5 Hz, OH), 1.44 (s, 3H), 1.43 (s,
3H); 13C NMR (CDCl3) δ 134.2 (C), 111.1 (C), 123.9 (CH), 76.7
(CH), 76.3 (CH), 72.0 (CH), 60.9 (CH), 27.3 (CH3), 26.3 (CH3);
MS (CI, 70 eV) m/z (rel. intensity) 246 (M+ + 1, 3.0), 160 (3.0),
145 (20), 101 (15.0), 96 (15.0), 59 (100). Anal. Calcd for
C9H12ClN3O3: C, 44.00; H, 4.92; N, 17.11. Found: C, 44.34;
H, 4.96; N, 16.96.
(d, J ) 7.5 Hz, 1H), 4.65 (dd, J ) 2.7, 7.4 Hz, 1H), 3.75 (m,
6H), 2.47 (t, J ) 6.6 Hz, 1H), 2.12 (s, 3H), 1.63 (s, 3H), 1.41 (s,
3H); 13C NMR (CDCl3) δ 170.5 (C), 168.5 (C), 111.3 (C), 75.8
(CH), 75.3 (CH), 69.9 (CH), 63.4 (CH), 61.5 (CH2), 52.3 (CH),
26.2 (CH3), 25.4 (CH3), 20.6 (CH3); MS (CI, 70 eV) m/z (rel.
intensity) 318 (M+ + 1, 3), 290 (40), 260 (50), 142 (100), 114
(80). Anal. Calcd for C12H19N3O7: C, 45.42; H, 6.04. Found:
C, 45.41; H, 6.06.
(2S,3R,4R,5S)-5-Azid o-4-(a cet yloxy)h exa n a l 2,3,4,6-
Tetr ol (19b). The title compound was synthesized using the
same general procedure adopted for the synthesis of lactols
20a -c. Conversion of crude 15b to 19b was accomplished by
treatment with NaBH4 (0.5 equiv at a time) in MeOH at 0 °C:
yield 50-60%; Rf ) 0.46 (hexanes/EtOAc, 1:1); IR (neat) 3440,
(3S,4R,5R,6S)-4-Acet yl-3-a zid o-1-ch lor o-5,6-O-isop r o-
p ylid en e-1-cycloh exa n e-4,5,6-tr iol (14b). Azido alcohol
4b1b (1.48 g, 6.04 mmol) was treated with acetic anhydride
(5.0 equiv) and pyridine (2.0 mL) under N2. After 2 h, the
volatile components were removed (high vacuum, overnight).
Column chromatography (hexanes/EtOAc, 7:3) of the resulting
yellowish-white crystals afforded 14b (1.73 g, 99% yield) as a
1
2990, 2960, 2105, 1750 cm-1; H NMR (CDCl3) δ 5.45 (d, J )
2.4 Hz, 1H), 4.71 (dd, J ) 3.4, 5.9 Hz, 1H), 4.65 (d, J ) 5.9 Hz,
1H), 4.29 (m, 2H), 4.22 (m, 1H), 3.95 (m, 1H), 2.77 (d, J ) 2.5
Hz, 1H), 2.12 (3H, s), 1.47 (3H, s), 1.30 (3H, s); 13C NMR
(CDCl3) δ 172.0 (C), 113.9 (C), 101.1 (CH), 85.9 (CH), 79.9 (CH),
79.6 (CH), 63.5 (CH2), 60.2 (CH), 26.1 (CH3), 24.8 (CH3), 20.2
(CH3). Anal. Calcd for C11H17N3O6: C, 45.99; H, 5.97.
Found: C, 45.88; H, 5.94.
white crystalline solid: Rf ) 0.58 (hexanes/EtOAc, 1:1); [R]21
D
) +66.1 (c 1.0, CHCl3); mp ) 55-56 °C; IR (neat) ν 2995, 2095,
1
1655 cm-1; H NMR (CDCl3) δ 5.92 (d, J ) 2.7 Hz, 1H), 5.18
(t, J ) 7.9 Hz, 1H), 4.58 (dd, J ) 1.1, 5.9 Hz, 1H), 4.25 (dd, J
) 5.9, 8.0 Hz, 1H), 3.95 (ddd, J ) 1.0, 2.7, 7.5 Hz, 1H), 2.12 (s,
3H), 1.53 (s, 3H), 1.39 (s, 3H); 13C NMR (CDCl3) δ 169.5 (C),
133.0 (C), 125.1 (CH), 111.9 (C), 75.4 (CH), 75.2 (CH), 71.4
(CH), 59.1 (CH), 27.6 (CH3), 26.2 (CH3), 20.8 (CH3); MS (CI,
70 eV) m/z (rel. intensity) 272 (M+ - 15, 15), 245 (50), 230
(18), 187 (15), 160 (100), 142 (45). Anal. Calcd for
Gen er a l P r oced u r e for th e F or m a tion of La ctols 20a-
c. Excess O3/O2 was bubbled through a 0.4 M solution of azido
alcohol 4 in methanol, cooled in a dry ice/acetone bath, until
a persistent blue color was observed (=30 min). After the
solution had been purged with N2 for 30 min at -78 °C, the
reaction flask was placed in an ice bath. NaBH4 (2.5 equiv,
assuming 1 mol of hydride/mol of NaBH4) was slowly added
so that the reaction temperature did not exceed 10 °C. (Note:
The reduction is routinely performed with the round-bottomed
C
11H14ClN3O4: C, 45.92; H, 4.91. Found: C, 45.93; H, 4.94.
(2S,3R,4R,5S)-4-Acet yl-5-a zid o-2,3-O-isop r op ylid en e-
h exa n oic Acid Meth yl Ester 2,3,4,6-Tetr ol (16b). Excess
O3/O2 was bubbled through a solution of vinyl chloride 14b
(814 mg, 2.83 mmol) in MeOH (10.0 mL) at -78 °C. After 30

518 J . Org. Chem., Vol. 63, No. 3, 1998
Nugent and Hudlicky
flask open to the atmosphere.) After 45 min the ice bath was
removed, and stirring continued for another 15 min. If the
reduction was not complete (TLC analysis) more NaBH4 was
added slowly at rt (0.3 equiv of NaBH4, stir for 20 min, check
by TLC). This routine was repeated until the reduction was
complete. (Note: Overreduction can occur!) The reaction
mixture was acidified with aqueous HCl (1.0 M), pH 4.5 ((0.5),
and extracted with EtOAc (×4). The combined organic ex-
tracts were washed with brine, dried (MgSO4), and evaporated.
Column chromatography using gradient elution (hexanes/
EtOAc, 65:35 f 1:1) provided 20 (70-80% yield) as a clear
oil.
varied from 1 to 6 h. After the reaction solution was saturated
with NaCl, the product was extracted with EtOAc/2-propanol
(1:1) until no more product could be detected in the aqueous
layer (TLC analysis). The combined organic extracts were
saturated with NaCl, decanted, dried (MgSO4), and concen-
trated. Column chromatography (hexanes/EtOAc, 1:3) pro-
vided 22 (55-65%) as a clear oil. (Note: The propensity of
these lactols to interconvert between the two anomeric forms
makes quantitative interpretation of the 1H NMR data almost
impossible; Aldehyde resonances were also observed.)
(2S,3S)-2-H yd r oxy-3-a zid o-γ-b u t yr ola ct ol (22a ): ob-
tained following the general procedure; Rf ) 0.35 (CH2Cl2/
(2S ,3S ,4S )-2,3-O-Isop r op ylid e n e -4-(1(S )-a zid o-2-h y-
d r oxyeth yl)-γ-bu tyr ola ctol (20a ) (Note: Both anomeric
acetone, 3:1); [R]23 ) +39.6 (c 1.2, acetone); IR (film) 3400,
D
1
2105, 1660, 1640 cm-1; H NMR (DMSO-d6) δ 6.38 (m, 1H),
1
lactols were evident in the H and 13C NMR spectra, but one
5.60 (d, J ) 4.39 Hz, 1H), 5.30 (d, J ) 6.83 Hz, 1H) 5.06 (t, J
) 5.42, 4.52 Hz, 1H), 5.00 (dd, J ) 4.6, 1.3 Hz, 1H), 4.02 (m,
3H), 3.80 (m, 2H), 3.70 (m, 1H), 3.40 (m, 2H); 13C NMR
(DMSO-d6) δ 102.5 (CH), 95.7 (CH′), 80.4 (CH), 75.8 (CH′), 65.3
(CH), 64.7 (CH′), 68.3 (CH2), 66.7 (CH2′); MS (CI 70 eV) m/z
(rel. intensity) 128 (M+ - 17, 15), 118 (8), 103 (6), 88 (93), 85
(54), 73 (30), 60 (100). Anal. Calcd for C4H7N3O3: C, 33.11;
H, 4.86. Found: C, 33.37; H, 4.98.
anomeric form predominated (9:1 ratio, 10-20 mg in 0.5 mL
of CDCl3): Rf ) 0.29 (hexanes/EtOAc, 1:1); [R]21 ) +31.0 (c
D
0.97, CHCl3); IR (neat) 3400, 2995, 2940, 2115, 2095, 1755,
1
1725 cm-1; H NMR (CDCl3) δ 5.40 (s, 1H), 4.73 (dd, J ) 5.9,
3.6 Hz, 1H), 4.61 (d, J ) 5.9 Hz, 1H), 4.24 (dd, J ) 8.8, 3.4 Hz,
1H), 4.11 (br d, J ) 2.0 Hz, 1H), 3.82 (m, 2H), 3.71 (m, 1H),
2.92 (br t, J ) 5.5 Hz, 1H), 1.44 (s, 3H), 1.29 (s, 3H); 13C NMR
(CDCl3) δ 112.9 (C), 100.9 (CH), 85.9 (CH), 79.9 (CH), 79.5
(CH), 63.5 (CH), 62.1 (CH2), 25.9 (CH3), 24.8 (CH3); MS (CI,
70 eV) m/z (rel. intensity) 246 (M+ + 1, 0.5), 230 (12), 218 (2),
202 (2.5), 159 (20), 73 (25), 59 (100). Anal. Calcd for
C9H15N3O5: C, 44.08; H, 6.16; N, 17.13. Found: C, 44.25; H,
6.29; N, 17.09.
(2R,3S)-2-H yd r oxy-3-a zid o-γ-b u t yr ola ct ol (22b ): ob-
tained following the general procedure; Rf ) 0.29 (CH2Cl2/
acetone, 3:1); [R]25 ) +5.47 (c 1.2, acetone); IR (film) 3400,
D
2950, 2900, 2500, 2105, 1725, 1650 cm-1; 1H NMR (DMSO-d6)
δ 6.39 (d, J ) 5.2 Hz, OH), 5.70 (d, J ) 5.1 Hz, OH), 5.00 (dd,
J ) 5.2, 2.3 Hz, 1H), 3.95 (m, 3H), 3.63 (dd, J ) 9.0, 4.0 Hz,
1H); 13C NMR (DMSO-d6) δ 101.8 (CH), 77.2 (CH), 67.5 (CH2),
61.1 (CH); MS (CI 70 eV) m/z (rel. intensity) 128 (M+ - 17,
45), 118 (8), 103 (12), 100 (13), 85 (68), 72 (46), 60 (100).
(2R,3R)-2-H yd r oxy-3-a zid o-γ-b u t yr ola ct ol (22c): ob-
tained following the general procedure; Rf ) 0.32 (CH2Cl2/
(2S ,3S ,4R )-2,3-O-Isop r op ylid e n e -4-(1(S )-a zid o-2-h y-
d r oxyeth yl)-γ-bu tyr ola ctol (20b) (Note: Both anomeric
1
lactols were evident in the H and 13C NMR spectra, but one
anomeric form predominated (2:1 ratio, 15-20 mg in 0.5 mL
of CDCl3). This ratio changed to approximately 3:1 when 3
mg of 20b was used. Because of the lactol equilibrium, the
acetone, 3:1); [R]23 ) -35.8 (c 0.94, acetone); IR (film) 3400,
D
integration for individual resonance patterns in the H NMR
2105, 1660, 1640 cm-1
;
1H NMR (DMSO-d6) δ 6.40 (d, 1H),
1
will not always correspond.): Rf ) 0.26 (hexanes/EtOAc, 1:1);
6.2 (d, 1H), 5.75 (d, J ) 4.4 Hz, 1H), 5.30 (m, 1H), 5.06 (m,
2H), 3.92 (m, 6H), 3.60 (m, 2H); 13C NMR (DMSO-d6) δ 103.1
(CH), 95.9 (CH′), 80.7 (CH), 76.0 (CH′), 65.5 (CH), 64.9 (CH′),
68.6 (CH2), 67.0 (CH2′); MS (CI 70 eV) m/z (rel. intensity) 128
(M+ - 17, 11), 118 (6), 88 (85), 85 (42), 60 (100).
[R]23 ) +11.7 (c 0.94, CHCl3); IR (neat) 3430, 2995, 2950,
D
2100, cm-1; 1H NMR (CDC13) δ 5.44 (s, 1H), 5.38 (d, J ) 3.83
Hz, 0.5H), 4.83 (dd, J ) 6.0, 1.1 Hz, 1H), 4.72 (dd, J ) 6.8, 2.8
Hz, 0.5H), 4.67 (dd, J ) 6.9, 3.9 Hz, 0.5H), 4.61 (d, J ) 5.92
Hz, 1H), 4.1 (dd, J ) 5.5, 2.8 Hz, 0.5H), 4.06 (dd, J ) 9.36,
1.22 Hz, 1H), 3.97 (dd, J ) 11.8, 4.0 Hz, 1H), 3.81 (m, 2.5 H),
3.62 (m, 1.5H), 1.55 (s, 1.5H), 1.46 (s, 3H), 1.38 (s, 1.5H), 1.31
(s, 3H); 13C NMR (CDCl3) δ 115.2 (C), 112.9 (C), 103.2 (CH),
96.5 (CH), 86.0 (CH), 85.7 (CH), 82.3 (CH), 80.9 (CH), 80.7
(CH), 79.5 (CH), 64.6 (CH), 64.2 (CH), 62.9 (CH2), 62.4 (CH2),
26.5 (CH3), 26.2 (CH3), 24.9 (CH3); MS (CI, 70 eV) m/z (rel.
intensity) 246 (M+ + 1, 4), 218 (23), 202 (25), 200 (25), 188
(41), 159 (64), 142 (61), 69 (69), 59 (100). Anal. Calcd for
C9H15N3O5: C, 44.08; H, 6.16; N, 17.13. Found: C, 43.93; H,
6.19; N, 17.31.
Gen er a l P r oced u r e for t h e F or m a t ion of 23a ,b a n d
24a ,b. To a flame-dried round-bottomed flask under Ar was
added n-tetradecyltriphenylphosphonium bromide (3.20 equiv).
After 30 min under high vacuum, the flask was flooded with
Ar, and THF was added until a 1.0 M solution was obtained.
The solution was cooled in an ice bath, and n-BuLi (2.75 equiv,
2.0 M in hexanes) was added, resulting in an immediate color
change (brown/yellow). After 5 min the ice bath was removed,
the solution stirred for another 15 min, and then lactol 22 (1.0
equiv) in THF (0.7 M) was added. After 5 h the reaction was
quenched with saturated NH4Cl and the mixture extracted
with EtOAc. The combined extracts were dried (MgSO4) and
concentrated, providing a viscous residue. Column chroma-
tography using gradient elution (15% EtOAc in hexanes f 30%
EtOAc in hexanes) provided cis- (23) and trans-azidosphin-
(2S,3S,4R)-2,3-O-Isop r op ylid e n e -4-(1(R)-a zid o-2-h y-
d r oxyeth yl)-γ-bu tyr ola ctol (20c) (Note: Both anomeric
lactols are evident in the 1H and 13C NMR spectra. One
anomeric form predominates (15:1 ratio).): Rf ) 0.25 (hexanes/
EtOAc, 1:1); [R]24D ) -13.7 (c 1.0, CHCl3); mp ) 89-91 °C; IR
1
gosine (24) (4:1 ratio, respectively, H NMR analysis).
1
(neat) 3425, 2995, 2945, 2105 cm-1; H NMR (CDCl3) δ 5.39
D -er yt h r o-(2S ,3R ,4Z )-2-Az i d o o c t a d e c e n e -1,3-d i o l
(23a ): cis isomer isolated in 14% yield; Rf ) 0.43 (hexanes/
(d, J ) 2.3 Hz, 1H), 4.85 (dd, J ) 5.8, 3.7 Hz, 1H), 4.62 (d, J
) 5.9 Hz, 1H), 4.17 (dd, J ) 9.1, 3.6 Hz, 1H), 3.94 (br d, 1H),
3.82 (m, 2H), 3.55 (br s, OH), 2.60 (br s, OH), 1.47 (s, 3H),
1.36 (s, 3H); 13C NMR (CDCl3) δ 112.9 (C), 101.3 (CH), 88.9
(CH), 85.5 (CH), 79.8 (CH), 62.9 (CH), 62.4 (CH2), 25.9 (CH3),
24.8 (CH3); MS (CI, 70 eV) m/z (rel. intensity) 246 (M+ + 1, 9),
230 (49), 218 (57), 202 (22). Anal. Calcd for C9H15N3O5: C,
44.08; H, 6.16; N, 17.13. Found: C, 44.17; H, 6.21; N, 17.23.
Gen er a l P r oced u r e for th e F or m a tion of La ctols 22a-
c. Amberlyst 15 (wet) ion-exchange resin (4.0 wt equiv with
respect to 20) was added to a 0.1 M solution of lactol 20 in
distilled H2O. After 5 h at 65 °C the reaction mixture was
filtered through a glass sinter. The pH of the filtrate was
adjusted to 7.0 ((0.5) with satd aq NaHCO3, and H2O was
added until a 0.05 M (with respect to 20) solution was
achieved. NaIO4 (1.0 equiv with respect to 20) was added to
the the reaction mixture, which had been protected from light.
Depending on the diastereomer of 20 used, reaction times
1
EtOAc, 2:1); H NMR (CDCl3) δ 5.67 (dtd, J ) 0.8, 7.5, 11.0
Hz, 1H), 5.45 (tt, J ) 1.5, 10.9 Hz, 1H), 4.58 (ddd, J ) 0.9,
5.8, 8.8 Hz, 1H), 3.77 (m, 2H), 3.49 (q, J ) 5.4 Hz, 1H), 2.19
(br s, 2H), 2.08 (m, 2H), 1.23 (m, >22H), 0.85 (t, J ) 6.8 Hz,
3H).
D -er yt h r o-(2S ,3R ,4E )-2-Az i d o o c t a d e c e n e -1,3-d i o l
(24a ): trans isomer isolated in 3.8% yield; Rf ) 0.38 (hexane/
EtOAc, 2:1); [R]24D ) -34.1 (c 1.58, CHCl3) (lit.8h [R]20D ) -32.9
(c 4.0, CHCl3)); 1H NMR (CDCl3) δ 5.80 (dtd, J ) 0.7, 6.7, 15.4
Hz, 1H), 5.51 (ddt, J ) 1.3, 7.3, 15.4 Hz, 1H), 4.23 (t, J ) 6.4
Hz, 1H), 3.77 (m, 2H), 3.45 (q, J ) 5.3 Hz, 1H), 2.05 (q, J )
7.0 Hz, 2H), 1.94 (br s, 2H), 1.23 (m, >22H), 0.86 (t, J ) 6.8
Hz, 3H).
L-th r eo-(2S,3S,4Z)-2-Azid oocta d ecen e-1,3-d iol (23b): cis
isomer isolated in 24.4% yield; Rf ) 0.52 (hexane/EtOAc, 2:1);
1H NMR (CDCl3) δ 5.64 (dt, J ) 7.5, 11.1 Hz, 1H), 5.44 (tt, J
) 1.5, 9.9 Hz, 1H), 4.53 (m, 1H), 3.79 (m, 1H), 3.65 (m, 1H),

Stereoisomers of Sphingosine from Chlorobenzene
J . Org. Chem., Vol. 63, No. 3, 1998 519
3.44 (dt, J ) 4.1, 6.3 Hz, 1H), 2.06 (m, 4H), 1.23 (m, >22H),
0.86 (t, J ) 6.6 Hz, 3H); 13C NMR (CDCl3) δ 135.7 (CH), 127.7
(CH), 68.4 (CH), 68.1 (CH), 62.8 (CH2), 31.9 (CH2), 29.64 (CH2),
29.56 (CH2), 29.5 (CH2), 29.3 (CH2), 28.0 (CH2), 22.7 (CH2),
14.0 (CH3).
) 1.4, 7.1, 15.4 Hz, 1H), 4.21 (t, J ) 6.5 Hz, 1H), 3.81 (dd, J
) 4.3, 11.5 Hz, 1H), 3.71 (dd, J ) 6.3, 11.5 Hz, 1H), 3.44 (dt,
J ) 4.3, 6.0 Hz, 1H), 2.04 (q, J ) 6.7 Hz, 2H), 1.63 (br s, >2H),
1.36 (m, 2H), 1.23 (m, >22H), 0.86 (t, J ) 6.6 Hz, 3H).
Gen er al P h otoisom er ization P r ocedu r e: cis-23 f trans-
24 or cis-27 f trans-28. To a mixture of cis- and trans-
azidosphingosines under an Ar atmosphere were added 1 vol
of dioxane and 3 vol of hexane by means of a syringe (molarity
of solution, 0.01 M). The solution was degassed by bubbling
Ar through it for 20 min. Diphenyl disulfide was added (0.3
equiv); the Pyrex round-bottomed flask was placed 2.5-5.0 cm
from the photochemical lamp. The light source was a 450-W
Canrad-Hanovia, medium-pressure, quartz, mercury lamp.
(Note: In our initial communication1a we stated incorrectly
that a 400-W light source had been used.) Exposure of this
solution to the filtered light (Pyrex glass excludes light <280
nm)26 for 3 h provided the thermodynamic cis-trans equilib-
rium. (Note: The solution turned light-green.) Additional
diphenyl disulfide (0.15 equiv) was added if the isomerization
proceeded slowly. The solution was concentrated under
reduced pressure and purified as before. This provided an 80%
combined yield of trans- and cis-azidosphingosine in a 3:1 ratio,
respectively, with respect to the initial predominately cis
mixture of olefins.
L-th r eo-(2S,3S,4E)-2-Azid ooct a d ecen e-1,3-d iol (24b ):
trans isomer isolated in 6.1% yield; Rf ) 0.45 (hexane/EtOAc,
2:1); [R]24D ) +3.11 (c 0.53, CHCl3); IR (neat) 3360, 2920, 2855,
1
2095, 1520 cm-1; H NMR (CDCl3) δ 5.78 (dtd, J ) 0.7, 6.7,
15.4 Hz, 1H), 5.50 (ddt, J ) 1.4, 7.1, 15.4 Hz, 1H), 4.19 (t, J )
6.5 Hz, 1H), 3.80 (dd, J ) 4.3, 11.5 Hz, 1H), 3.68 (dd, J ) 6.3,
11.5 Hz, 1H), 3.45 (dt, J ) 4.3, 6.0 Hz, 1H), 2.04 (q, J ) 6.7
Hz, 2H), 1.63 (br s, >2H), 1.22 (m, >22H), 0.86 (t, J ) 6.6 Hz,
3H); 13C NMR (CDCl3) δ 135.5 (CH), 128.4 (CH), 73.6 (CH),
67.8 (CH), 63.0 (CH2), 32.3 (CH2), 31.9 (CH2), 29.7 (CH2), 29.5
(CH2), 29.3 (CH2), 29.2 (CH2), 29.0 (CH2), 22.7 (CH2), 14.0
(CH3). Anal. Calcd for C18H35N3O2: C, 66.42; H, 10.84; N,
12.91. Found: C, 66.87; H, 10.70; N, 12.41.
D-th r eo-(2R,3R,4Z)-2-Azid o-4-octa d ecen e-1,3-d iol (23d )
a n d
D-th r eo-(2R,3R,4E)-2-Azid o-4-oct a d ecen e-1,3-d iol
(24d ). To a flame-dried round-bottomed flask under Ar was
added n-tetradecyltriphenylphosphonium bromide (359 mg,
0.67 mmol, 3.50 equiv). After 30 min under high vacuum Ar
was introduced. THF (2.50 mL) was added, and the solution
was cooled in an ice bath. After 15 min, sodium amylate34
(0.27 M, 2.5 mL, 3.5 equiv) was added. The solution im-
mediately became orange. After 15 min the ice bath was
removed. After 30 min at rt the ylide solution was cooled to
0 °C, and lactol 32d (72.9 mg, 0.190 mmol, 1.0 equiv) in THF
(1.5 mL) was added dropwise over 1 min. After 30 min the
ice bath was removed, and the reaction mixture stirred for 1
h at rt. After the solution was cooled to -55 °C, the reaction
was quenched with saturated NH4Cl (10 mL), and the mixture
was extracted with EtOAc (×3). The organic extracts were
combined, dried (MgSO4), and concentrated providing a viscous
dark oil. Column chromatography using gradient elution
(100% hexanes f hexanes/EtOAc, 6:1) provided 32 mg of
impure sphingosine adducts 34d and 35d . Further attempts
at purification were futile; the major impurity was tert-
butyldiphenylsilanol. 1H NMR of the impure silyloxy azi-
dosphingosine indicated a 9:1 cis:trans ratio of olefinic isomers.
(Note: When the lactol 32d was added at rt, to the ylide, a
6:4 cis:trans ratio was found.)
34d a n d 35d : 1H NMR (CDCl3) δ 7.67 (m, 4H), 7.42 (m,
6H), 5.72 (m, 0.1H, trans), 5.55 (dt, J ) 7.3, 11.0 Hz, 0.9H,
cis), 5.38 (m, 1H), 4.43 (m, J ) 4.8 Hz av, 0.9H, cis), 4.13 (q,
J ) 5.6 Hz, 0.1H, trans), 3.8 (m, 4H), 3.42 (m, 2H), 1.99 (m,
2H), 1.26 (s, 22H), 0.89 (t, J ) 6.9 Hz, 3H).
The crude silyloxy azidosphingosine products (34d and 35d )
were treated with n-Bu4NF-hydrate (40 mg) in THF (2.0 mL),
followed by addition of H2O, extraction (EtOAc), and concen-
tration. The resulting oil was subjected to column chroma-
tography (gradient elution, hexanes/EtOAc, 6:1 f 7:3) to
provide 23d and 24d (8.3 mg, 13% yield from 32d ).
For further examples of this type of photoisomerization,
albeit without an azide present, see refs 8g and 11h.
L-er yth r o-(2S,3R)-Tr ia cetylsp h in gosin e (tr a n s-25c a n d
cis-26c). A 1:1 (1H NMR analysis) mixture of inseparable cis-
26c and trans-25c was obtained after photoisomerization of
the 6:1 cis:trans mixture of acetamides 27d and 28c and
peracylation: [R]27 ) +8.2 (c 0.9, CHCl3).31 See General
D
Photoisomerization Procedure for experimental details.
(3R,4S,5R,6S)-3-Azido-4-(ter t-bu tyldiph en ylsilyl)-1-ch lo-
r o-5,6-O-isop r op ylid en ecycloh ex-1-en e-4,5,6-tr iol (29d ).
To a solution of alcohol 4d 1a (2.30 g, 9.37 mmol) in THF (10.0
mL) were added tert-butyldiphenylsilyl chloride (5.07 g, 18.5
mmol, 2.00 equiv) and imidazole (1.52 g, 22.4 mmol, 2.39
equiv). After 4 h at reflux the reaction mixture was cooled to
rt and stirred for another 12 h. (Note: As the reaction proceeds
a white precipitate, which we assume to be the hydrochloride
salt of imidazole, accumulates.) The solution was filtered
through Celite (rinsed with CH2Cl2), and the filtrate was
washed with saturated aq NH4Cl and brine. The organic
extracts were dried (MgSO4) and evaporated to give 7.21 g of
a viscous brown oil. Column chromatography using gradient
elution (100% hexanes f 3% EtOAc in hexanes) provided 29d
(3.85 g, 85%) as a viscous clear oil: Rf ) 0.45 (hexanes/EtOAc,
9:1); [R]24 ) -62.5 (c 0.95, CHCl3); IR (neat) ν 3075, 3050,
D
2985, 2930, 2105 cm-1; H NMR (CDCl3) δ 7.78 (m, 4H), 7.40
1
(m, 6H), 5.73 (m, J ) 1.7 Hz, 1H), 4.37 (dm, J ) 8.7 Hz, 1H),
4.10 (m, 2H), 3.68 (dm, J ) 8.8 Hz, 1H), 1.42 (s, 3H), 1.27 (s,
3H), 1.09 (s, 9H); 13C NMR (CDCl3) δ 133.9 (C), 133.8 (C), 132.2
(C), 110.6 (C), 19.4 (C), 136.0 (CH), 135.9 (CH), 130.2 (CH),
129.9 (CH), 128.0 (CH), 127.6 (CH), 76.6 (CH), 76.4 (CH), 72.8
(CH), 61.7 (CH), 27.5 (CH3), 26.8 (CH3), 26.2 (CH3); MS CI m/z
(rel. intensity) 484 (M+, 0.52), 426 (17), 398 (38), 385 (36), 383
(100), 378 (34), 305 (37). Anal. Calcd for C25H30ClN3O3Si: C,
62.03; H, 6.25; N, 8.68. Found: C, 62.41; H, 6.52; N, 8.35.
(2S,3R,4S,5R)-5-Azid o-4-[(ter t-bu tyld ip h en ylsilyl)oxy]-
1,2-O-isop r op ylid en eh exa n oic Acid Meth yl Ester 2,3,4,6-
Tetr ol (30d ). Vinyl chloride 29d (3.74 g, 7.73 mmol) was
added to MeOH (50 mL) and gently heated to ensure dissolu-
tion. The reaction mixture was then cooled with a dry ice/
acetone bath, and O3/O2 was bubbled through the solution.
After 20 min the solution was saturated with O3, indicated by
a characteristic blue color, and TLC analysis indicated no
starting material remained. The reaction mixture was then
purged with N2 for 20 min at -78 °C. The reaction flask was
placed in an ice bath, and maintaining the temperature at 5
°C, three portions of NaBH4 (580 (15.3 mmol, 2.00 equiv), 220,
and finally 240 mg) were added, with 25-min intervals between
additions. (Note: Use lumps of NaBH4; if powdered NaBH4
is used, add slowly over 3-5 min.) Thirty minutes after the
last addition of NaBH4 the ice bath was removed, and the
reaction mixture stirred for another 20 min. Two more
D -t h r eo-(2R ,3R ,4Z)-2-Azid o -4-o c t a d e c e n e -1,3-d io l
1
(23d ): cis isomer isolated in 11.0% yield; H NMR (CDCl3) δ
5.66 (dtm, J ) 7.7, 11.0 Hz, 1H), 5.46 (ddt, J ) 1.5, 10.8, 10.8
Hz, 1H), 4.52 (m, 1H), 3.81 (m, 1H), 3.67 (m, 1H), 3.46 (ddd, J
) 4.1, 6.4, 6.4 Hz, 1H), 2.08 (m, 2H), 1.90 (m, 2H), 1.24 (s,
>20H), 0.90 (t, J ) 7.0 Hz, 1H); 13C NMR (CDCl3) δ 135.8 (CH),
127.5 (CH), 68.3 (CH), 68.0 (CH), 62.8 (CH2), 31.9 (CH2), 29.6
(CH2), 29.56 (CH2), 29.5 (CH2), 29.34 (CH2), 29.28 (CH2), 28.9
(CH2), 27.9 (CH2), 22.7 (CH2), 14.1 (CH3).
D -t h r eo-(2R ,3R ,4E )-2-Azid o -4-o c t a d e c e n e -1,3-d io l
(24d ): trans isomer isolated in 2% yield; Rf ) 0.30 (hexane/
1
EtOAc, 2:1); [R]24 ) -2.40 (c 0.27, CHCl3); H NMR (CDCl3,
D
300 MHz) δ 5.80 (dtd, J ) 0.7, 6.7, 15.4 Hz, 1H), 5.52 (ddt, J
(33) Wovkulich, P. M.; Shankaran, K.; Kiegiel, J .; Uskokovic, M. R.
J . Org. Chem. 1993, 58, 832.
(34) For the preparation of sodium amylate, see: Short, R. P.; Ranu,
J . M.; Hudlicky, T. J . Org. Chem. 1983, 48, 4453. The solution of
sodium amylate must be heated to 65 °C and transferred quickly to
the cooled solution of the phosphonium salt via syringe; otherwise, the
amylate salt precipitates in the syringe.

520 J . Org. Chem., Vol. 63, No. 3, 1998
Nugent and Hudlicky
portions of NaBH4 (340 mg, wait 20 min, then 107 mg) were
added. (Note: It is crucial to monitor the reaction by TLC after
each addition of NaBH4 (depending on the reaction, more or
less NaBH4 may be required).) Distilled H2O (150 mL) was
added, and the solution was acidified with 1.2 N HCl to pH
3.5 ( 0.5. The acidic solution was immediately extracted with
EtOAc (×4); the combined organic extracts were washed with
brine (×2), dried (MgSO4), and evaporated to provide a yellow
oil. Column chromatography (gradient elution, 15% f 40%
EtOAc in hexanes) provided 30d (3.59 g, 91%) as a viscous
4.28 (dd, J ) 5.2, 9.8 Hz, 1H), 4.18 (dd, J ) 4.6, 9.8 Hz, 1H′;
d, J ) 1.5 Hz, 1H), 4.12 (dd, J ) 2.2, 4.0 Hz, 1H′), 4.01 (dd, J
) 2.3, 9.8 Hz, 1H), 3.96 (d, J ) 9.8 Hz, OH′), 3.76 (dt, J ) 1.7,
5.0 Hz, 1H), 3.66 (ddd, J ) 0.5, 2.1, 9.8 Hz, 1H′), 3.62 (m, J )
2.1, 4.6 Hz, 1H′), 2.63 (d, J ) 7.9 Hz, OH), 1.13 (s, 9H), 1.09
(s, 9H); 13C NMR (CDCl3) δ 132.7 (C), 132.4 (C), 132.0 (C),
131.4 (C), 19.1 (C), 19.0 (C), 135.6 (CH), 135.58 (CH), 130.6
(CH), 130.5 (CH), 130.24 (CH), 130.19 (CH), 128.2 (CH), 128.1
(CH), 128.0 (CH), 127.9 (CH), 103.5 (CH), 97.0 (CH), 81.1 (CH),
76.5 (CH), 66.2 (CH), 65.9 (CH), 71.2 (CH2), 68.2 (CH2), 26.9
(CH3), 26.8 (CH3).
clear oil: Rf ) 0.33 (hexanes/EtOAc, 2:1); [R]24 ) +29.6 (c
D
1.6, CHCl3); IR (neat) ν 3500, 3070, 3050, 2980, 2950, 2100,
1755 cm-1; 1H NMR (CDCl3) δ 7.72 (m, 4H), 7.41 (m, 6H), 4.40
(ddm, J ) 3.9, 6.9 Hz, 1H), 4.22 (m, 2H), 3.52 (m, 6H), 1.57 (s,
3H), 1.31 (s, 3H), 1.05 (s, 9H); 13C NMR (CDCl3) δ 170.3 (C),
133.3 (C), 133.0 (C), 110.6 (C), 19.6 (C), 136.0 (CH), 135.9 (CH),
130.0 (CH), 127.8 (CH), 127.7 (CH), 80.1 (CH), 75.4 (CH), 70.4
(CH), 64.6 (CH), 51.8 (CH), 62.3 (CH2), 27.0 (CH3), 26.4 (CH3),
25.1 (CH3); MS CI m/z (rel. intensity) 514 (M+ + 1, 2), 487
(33), 486 (100), 428 (73.6), 408 (60), 379 (12), 378 (73), 358
(31), 291 (45), 220 (49). Anal. Calcd for C26H35N3O6Si: C,
60.80; H, 6.87; N, 8.18. Found: C, 61.16; H, 7.15; N, 7.87.
(2S,3R,4S,5R)-5-Azid o-4-[(ter t-bu tyld ip h en ylsilyl)oxy-
]h exa n oic Acid Meth yl Ester 2,3,4,6-Tetr ol (31d ). Ac-
etonide 30d (1.73 g, 3.37 mmol) was added to 1% I2 in MeOH
(30 mL, w/v) and heated at 45 °C with stirring for 46 h. The
reaction was quenched with saturated sodium thiosulfate
(Na2S2O3) (80 mL) and the mixture extracted with EtOAc (×3).
The combined organic extracts were dried (MgSO4) and
evaporated. Column chromatography of the ensuing viscous
oil using gradient elution (25% f 50% EtOAc in hexanes)
provided 31d (1.28 g, 80% yield) as a white solid. (Note: Four
inches of silica gel are sufficient and optimal. This product is
prone to silyl migration and lactonization on prolonged expo-
sure to silica gel. If the reaction is performed at higher
temperatures, three new products (36d , 37d , 38d ) appear.32
Compound 36d was judged to be too unstable for analysis; 37d
and 38d were fully identified.) Vicinal diol 31d : Rf ) 0.19
(2S,3R)-3-Azid o-1-[(ter t-bu tyld ip h en ylsilyl)oxy]-2-h y-
d r oxy-γ-bu tyr ola ctol (33d ): The procedure used to make
lactol 32d also provided 134.4 mg (0.350 mmol, 13%) of the
anomeric silyloxy-protected lactol 33d ; Rf ) 0.45 (hexanes/
EtOAc, 4:1); [R]25 ) -86.2 (c 1.30, CHCl3); IR (neat) ν 3505,
D
3070, 3050, 2955, 2100 cm-1; 1H NMR (CDCl3) δ 7.67 (m, 4H),
7.43 (m, 6H), 5.41 (d, J ) 3.7 Hz, 1H), 4.20 (dd, J ) 5.7, 9.7
Hz, 1H), 4.13 (m, 2H), 3.66 (dd, J ) 4.4, 9.0 Hz, 1H), 2.91 (d,
J ) 7.5 Hz, OH), 1.12 (s, 9H); 13C NMR (CDCl3) δ 132.5 (C),
132.4 (C), 19.2 (C), 135.6 (CH), 135.5 (CH), 130.2 (CH), 130.1
(CH), 127.9 (CH), 127.8 (CH), 97.2 (CH), 77.2 (CH), 66.1 (CH),
68.6 (CH2), 26.8 (CH3).
(2S,3R,4S)-2-Hyd r oxy-3-[(ter t-bu tyld ip en ylsilyl)oxy]-4-
(1(R)-a zid o-2-h yd r oxyeth yl)-γ-bu tyr ola cton e (37d ): pro-
cedure used to synthesize diol 31d also provided lactone 37d ;
Rf ) 0.45 (hexanes/EtOAc, 1:1); [R]24D ) -45.3 (c 1.03, CHCl3);
mp ) 104-105 °C; IR (KBr) ν 3350, 3070, 3045, 2940, 2105,
1790, 1775 cm-1 1H NMR (CDCl3) δ 7.66 (m, 4H), 7.46 (m,
;
6H), 4.57 (m, 1H) (Note: When a drop of D2O is added the
multiplet is simplified to a d, J ) 6.0 Hz, 1H), 4.34 (d, J ) 5.9
Hz, 1H), 3.99 (d, J ) 2.1 Hz, 1H), 3.61 (dd, J ) 7.7, 11.2 Hz,
1H), 3.44 (dd, J ) 5.4, 11.2 Hz, 1H), 2.92 (br s, 1H, OH), 2.69
(m, 1H) (Note: When a drop of D2O is added the multiplet is
simplified to a septet, J ) 2.2, 5.4, 7.6 Hz, 1H), 1.64 (br s, 1H,
OH), 1.09 (s, 9H) (Note: If the 1H NMR solvent is DMSO-d6
or acetone-d6, a 1:1 mixture of 37d and 38d results almost
immediately.); 13C NMR (CDCl3) δ 174.8 (C), 132.5 (C), 131.4
(C), 19.2 (C), 135.7 (CH), 130.8 (CH), 130.6 (CH), 128.3 (CH),
83.2 (CH), 71.7 (CH), 68.2 (CH), 62.15 (CH), 62.24 (CH2), 26.9
(CH3); MS CI m/z (rel. intensity) 442 (M+ + 1, 2). Anal. Calcd
for C22H27N3O5Si: C, 59.84; H, 6.16; N, 9.52. Found: C, 59.46;
H, 6.15; N, 9.34.
(hexanes/EtOAc, 1:1); [R]24 ) +13.4 (c 1.00, CHCl3); mp )
D
78-82 °C; IR (KBr) ν 3470, 3430, 3350, 3075, 3050, 3000, 2950,
2095, 1755 cm-1; 1H NMR (DMSO-d6) δ 7.69 (m, 4H), 7.42 (m,
6H), 5.62 (d, J ) 5.9 Hz, OH), 5.31 (d, J ) 5.8 Hz, OH), 4.91
(t, J ) 5.2 Hz, OH), 4.27 (t, J ) 6.1 Hz, 1H), 3.83 (t, J ) 4.3
Hz, 1H), 3.76 (q, J ) 5.4 Hz, 1H), 3.66 (q, J ) 5.7 Hz, 1H),
3.52 (s, 3H), 3.37 (t, J ) 5.6 Hz, 2H), 0.98 (s, 9H); 13C NMR
(CDCl3) δ 172.9 (C), 132.8 (C), 19.5 (C), 136.0 (CH), 130.2 (CH),
127.9 (CH), 75.4 (CH), 71.8 (CH), 71.6 (CH), 64.5 (CH), 52.5
(CH), 61.4 (CH2), 27.0 (CH3).
(2S,3S,4S)-2-[(ter t-Bu tyld ip en ylsilyl)oxy]-3-h yd r oxy-4-
(1(R)-a zid o-2-h yd r oxyeth yl)-γ-bu tyr ola cton e (38d ): pro-
cedure used to synthesize diol 31d also provided lactone 38d ;
Rf ) 0.28 (hexanes/EtOAc, 1:1); [R]24D ) -77.2 (c 1.00, CHCl3);
mp ) 121-123 °C; IR (KBr) ν 3350, 3070, 2960, 2935, 2105,
1785, cm-1; 1H NMR (CDCl3) δ 7.82 (m, 2H), 7.69 (m, 2H), 7.47
(m, 6H), 4.65 (d, J ) 5.5 Hz, 1H), 4.44 (d, J ) 2.4 Hz, 1H),
3.81 (d, J ) 6.4 Hz, 1H), 3.78 (dd, J ) 0.8, 5.5 Hz, 1H), 3.61
(ddd, J ) 2.5, 6.4 Hz, 1H), 2.98 (br s, OH), 2.05 (br s, OH),
(2S,3R)-3-Azid o-2-[(ter t-bu tyld ip h en ylsilyl)oxy]-γ-bu -
tyr ola ctol (32d ). NaIO4 (1.15 g, 5.40 mmol, 2.00 equiv) was
added to a solution of vicinal diol 31d (1.28 g, 2.70 mmol) in
CH3OH/H2O (80 mL, 3:1). The reaction mixture was protected
from light and stirred. (Note: A white precipitate accumulates
as the reaction proceeds; it is not the product.) After 3 h
CH2Cl2 (80 mL) was added, and the resulting solution was
passed through a plug of Celite. H2O (80 mL) was added to
the filtrate, and the aqueous layer was extracted with CH2Cl2
(×3). The combined organic extracts were dried (MgSO4) and
evaporated to provide an oil. Column chromatography (gradi-
ent elution, 20% f 35% EtOAc/hexanes) provided 32d (778
mg, 75%) as a viscous clear oil. In addition 33d (134 mg, 13%),
the product of silyl migration, was isolated. (Note: Both
anomeric lactols are evident in the 1H and 13C NMR spectra
of 32d . The two anomers exist in an approximate ratio of 1:1.2
(10-20 mg in 0.5 mL of CDCl3).) TOCSY NMR established
the separate lactol resonances: Rf ) 0.28 (hexanes/EtOAc, 4:1);
1
1.16 (s, 9H) (Note: If the H NMR solvent is DMSO-d6, a 1:1
mixture of lactones 37d and 38d immediately ensues.); 13C
NMR (CDCl3) δ 173.3 (C), 132.2 (C), 131.0 (C), 19.3 (C), 135.9
(CH), 135.5 (CH), 130.6 (CH), 130.5 (CH), 128.1 (CH), 128.0
(CH), 82.1 (CH), 70.2 (CH), 69.5 (CH), 62.3 (CH), 62.8 (CH2),
26.8 (CH3); MS CI m/z (rel. intensity) 442 (M+ + 1, 2.5), 385
(11), 384 (43), 364 (100), 308 (83), 199 (34), 60 (52). Anal. Calcd
for C22H27N3O5Si: C, 59.84; H, 6.16; N, 9.52. Found: C, 59.83;
H, 6.23; N, 9.42.
Ack n ow led gm en t. The authors are grateful to the
National Science Foundation (CHE-9315684 and CHE-
9615112), Genencor International, Inc., and TDC Re-
search, Inc., for the financial support of this work.
[R]25 ) -2.22 (c 1.35, CHCl3); IR (neat) ν 3435, 3080, 2980,
D
2950, 2100 cm-1
;
1H NMR (CDCl3) δ 7.66 (m, 4H), 7.45 (m,
6H), 5.28 (dd, J ) 4.0, 9.8 Hz, 1H′), 5.25 (d, J ) 7.9 Hz, 1H),
J O971335A