Stereospecific synthesis of (+)-oxybiotin from D-xylose

Article abstract of DOI:10.1016/S0008-6215(01)00331-7

A new 14-step synthesis of (+)-oxybiotin, an oxygen analogue of (+)-biotin, was achieved starting from D-xylose by use of selected 2,5-anhydro sugar derivatives as key intermediates.

Full text of DOI:10.1016/S0008-6215(01)00331-7

Carbohydrate Research 337 (2002) 459–465
www.elsevier.com/locate/carres
Note
Stereospecific synthesis of (+)-oxybiotin from
D
-xyloseꢀ
Velimir Popsavin,* Goran Benedekovic´, Mirjana Popsavin, Dusˇan Miljkovic´
Faculty of Sciences, Institute of Chemistry, Uni6ersity of No6i Sad, Trg D. Obrado6ica 3, YU-21000 No6i Sad, Yugosla6ia
Received 22 October 2001; accepted 14 December 2001
Abstract
A new 14-step synthesis of (+)-oxybiotin, an oxygen analogue of (+)-biotin, was achieved starting from
D-xylose by use of
selected 2,5-anhydro sugar derivatives as key intermediates. © 2002 Elsevier Science Ltd. All rights reserved.
Keywords: (+)-Oxybiotin; Protected 2,5-anhydro pentoses; 2,3,4-Trisubstituted tetrahydrofuranes;
D-Xylose
Oxybiotin, a biotin analogue in which oxygen re-
places sulfur, was synthesized by Hofmann2 and shown
to exhibit a high biotin-like activity towards some
microorganisms.3 Accordingly, it was assumed that the
biologically active oxybiotin has the same absolute
configuration as that of the natural biotin. This as-
sumption was definitely proved by a stereospecific syn-
thesis of (+)-oxybiotin (18, Scheme 3) from
further introduction of the carboxyalkyl side chain, as
well as for building the final (+)-oxybiotin ureido
system.
Hydrolytic removal of the dioxolane protective group
in 1 gave a hydrated form of the corresponding alde-
hyde 2. Due to its instability,‡ the intermediate 2 was
promptly treated with 3-methoxycarbonyl-2-propenyli-
dene triphenylphosphorane,9 (generated in situ from the
corresponding phosphonium bromide), to afford the
a,b-unsaturated ester 3 as a mixture of E and Z iso-
mers. Subsequent catalytic hydrogenation of 3 over
PtO2 gave the corresponding saturated ester 4 (32%
from 1). Solvolysis of 4 in wet N,N-dimethylfor-
mamide, in the presence of calcium carbonate as a
proton acceptor, gave a mixture of regioisomers 5 with
inverted configuration at C-3. O-Debenzoylation of 5
with sodium methoxide in methanol afforded the ex-
pected diol 6. Reaction of 6 with mesyl chloride in
dichloromethane, in the presence of triethylamine, gave
the corresponding di-O-mesyl derivative 7 (15.3% from
1), a potential intermediate for the further introduction
of two azide functions with inversion of configuration
at C-3 and C-4.
D
-glucose.4 Apart of this 19-steps sequence, no further
attempts were made directed towards more efficient
preparations of the enantiopure (+)-18. Herein we
report a new 14-step stereospecific synthesis of (+)-
oxybiotin, based on
D
-xylose as a chiral precursor,1 by
way of selected 2,5-anhydro sugars† as convenient
intermediates.
Earlier we have described6,7 the five-step conversion
of
D-xylose to the 2,5-anhydro-D-xylose ethylene acetal
derivative 1 (Scheme 1). The key step of the sequence
(stereospecific formation of the trisubstituted tetra-
hydrofuran system) has been achieved according to the
methodology similar to that developed by Defaye and
Hildesheim.8 Compound 1 has the correct stereochem-
istry at C-2, as well as the functionalities suitable for
An alternative six-step sequence for the preparation
of intermediate 7 is presented in Scheme 2. Solvolysis of
1 in wet N,N-dimethylformamide, under the same reac-
ꢀ For a preliminary account, see Ref. 1.
* Corresponding author. Fax: +381-21-54065.
E-mail address: popsavin@ih.ns.ac.yu (V. Popsavin).
† For a review on 2,5-anhydro sugars, see Ref. 5.
‡ Compound 2 decomposes slowly on prolonged standing
at room temperature turning into tar.
0008-6215/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0008-6215(01)00331-7

460
V. Popsa6in et al. / Carbohydrate Research 337 (2002) 459–465
Scheme 1. Reagents and conditions: (a) TFA, 6 M HCl, rt, 12 h, 60%; (b) [Ph3PCH2CH:CHCO2Me]+ Br−, CH2Cl2, NaOH, H2O,
rt 1 h, 59%; (c) H2/PtO2, AcOH, rt, 20 h, 90%; (d) CaCO3, 95% aq DMF, 150 °C, 10 h, 65%; (e) NaOMe, MeOH, rt, 1 h, 81%;
(f) MsCl, Et3N, CH2Cl2, −10 °C, 0.5 h, 91%.
Scheme 2. Reagents and conditions: (a) CaCO3, 95% aq DMF, 150 °C, 10 h; (b) KOH/MeOH, 60 °C, 0.5 h; (c) MsCl, Py, rt, 24
h, 64% from 1; (d) TFA, 6 M HCl, rt, 24 h; (e) 2,4-DNPH, MeOH, H2SO4, rt, 0.5 h, 72%; (f) [Ph3PCH2CH:CHCO2Me]+ Br−,
CH2Cl2, NaOH, H2O, rt 45 min; (g) H2/PtO2, AcOH, rt, 18 h, 54% from 10.
in an overall yield of 64% with respect to the starting
compound 1. Hydrolysis of 10 with a mixture of hydro-
chloric and trifluoroacetic acid afforded the unstable
hydrated aldehyde 11, which was fully characterized
after its conversion to the corresponding 2,4-dinitro-
phenylhydrazone 12. Wittig olefination of 11, under the
conditions as described above, yielded 13 as an insepa-
rable mixture of E and Z isomers, which were then
converted to the desired intermediate 7 (54% from 10)
by catalytic hydrogenation over PtO2. Obviously the
six-step sequence realized via the 3,4-di-O-mesyl deriva-
tion conditions already used for the preparation of 5
(Scheme 1), afforded a mixture of regioisomers 8. Sub-
sequent O-debenzoylation of 8 with potassium hydrox-
ide gave the corresponding diol 9, which was finally
converted into the known7,10 di-O-mesyl derivative 10
by treatment with mesyl chloride in pyridine. All three
steps concerning the conversion of 1 to 10 were carried
out by a one-pot procedure, whereupon the intermedi-
ates 8 and 9 were used without any purification or
separation from accompanying inorganic impurities.
Pure 10 was isolated by short-column chromatography

V. Popsa6in et al. / Carbohydrate Research 337 (2002) 459–465
461
Scheme 3. Reagents and conditions: (a) NaN3, HMPA, 80 °C, 5 h, 71%; (b) NaN3, NH4Cl, DMF, 150 °C, 20 h, 47%; (c) H2/PtO2,
AcOH, Ac2O, rt, 23 h, 85%; (d) Ph3P, BnOCOCl, THF, rt, 5 h, then NH4OH, H2O, rt, 18 h, 24%; or H2/PtO2, CH2Cl2, rt, 6 h,
then Et3N, triphosgene, 0 °C, 1 h, rt 18 h, 68%; (e) Ba(OH)2, H2O, 100 °C, 1.5 h, 98%.
cific synthesis of (+)-oxybiotin (18) from
D-xylose,
tive 10 (Scheme 2) represents a more convenient proce-
dure for the preparation of 7, since it provided a
considerably higher overall yield (34.6% from 1), com-
pared to the six-step route presented in Scheme 1
(15.3% from 1).
alternative procedures for the conversion of 15 into 18
were also considered, in order to avoid the hazards of
handling of phosgene.4 At first, we have checked up if
the Staudinger reaction¶ in the presence of
a
chloroformate13 could be used for the direct conversion
of 15 into the imidazolidinone 17, analogously to the
one-pot conversion of vicinal azido alcohols to oxazo-
lidinones.14 Treatment of 15 with triphenylphosphine
and benzyl chloroformate, under reaction conditions
similar to those recently reported,13 afforded a low yield
of the desired imidazolidinone 17 (24%). However,
one-pot catalytic reduction of 15 followed by a subse-
quent triphosgene treatment provided the desired inter-
mediate 17 in 68% yield. Compound 17 was finally
converted to (+)-oxybiotin (18) by hydrolysis with
barium hydroxide in an almost quantitative yield. The
physical constants (mp and [h]D) of (+)-18 thus ob-
tained were in excellent agreement with those already
reported.4
Conversion of the intermediate 7 into the (+)-oxybi-
otin (18) is outlined in Scheme 3. In 1975 Ohrui and
Emoto11 described a solvolytic reaction of a thiophane
analogue of 7 (NaN3, HMPA, 80 °C) whereupon the
corresponding 3,4-diazido derivative was obtained in
high yield. The same reaction conditions were therefore
applied to the intermediate 7, but instead of the ex-
pected 3,4-diazido derivative 15, the 4-monoazide 14
was exclusively formed in 71% yield. However, a reac-
tion of 7 with sodium azide in N,N-dimethylformamide
at 150 °C for 20 h, in the presence of ammonium
chloride, gave the key intermediate 15 (37%) along with
14 (26%) as a byproduct.§ Compound 14, under similar
reaction conditions gave the same yield of 15 (37%).
Accordingly, by combining the last two procedures, the
desired product 15 can be prepared in 47% total yield,
which is comparable to that achieved earlier1 from the
triflic analogue of 7. Catalytic hydrogenation of 15 over
PtO2 in a mixture of glacial acetic acid and acetic
anhydride gave the corresponding diacetamido deriva-
tive 16, that can be converted to (+)-oxybiotin (18)
according to the reported procedure.4 Although the
preparation of 16 formally represents a new stereospe-
In summary, a new stereospecific synthesis of (+)-
oxybiotin has been developed starting from
D-xylose,
by utilizing cheap and readily available reagents and by
applying simple experimental procedures. Although this
new synthesis of 18 contains some low-yielding steps
(7“15, 14“15), it consists of less synthetic steps (14)
then the earlier preparation from
D
-glucose (19 steps).4
In addition, the new approach provided a convenient
one-pot procedure for the (+)-oxybiotin ureido system
building utilizing triphosgene, a safe and stable replace-
§ Prolongation of the reaction time did not increase the
yield of the desired product 15 presumably due to its instabil-
ity under the applied reaction conditions.
¶ For a review on the Staudinger reaction, see Ref. 12.

462
V. Popsa6in et al. / Carbohydrate Research 337 (2002) 459–465
ment of phosgene.15 Novel and more efficient ap-
proaches towards the key intermediate 15 and to the
target 18 itself are currently being investigated, and the
results will be reported in due course. Moreover, appro-
priate C-1 functionalization of the 2,5-anhydro deriva-
tives 2 or 11, may provide access to potential divergent
intermediates for the preparation of (+)-oxybiotin
analogues with the side chain containing an additional
heteroatom (e.g., O or S) instead of the C-2% methylene
group.16
residue gave 3 (0.804 g, 59%) as a bright-yellow syrup:
[h]D −9.78° (c 0.87, CHCl3); wmax (film): 1725, 1655,
1600, 1375, 1200–1180 cm−1. A solution of 3 (0.74 g,
1.57 mmol) in glacial AcOH (15 mL) was hydrogenated
over PtO2 (0.08 g, 0.35 mmol) for 20 h at rt. The
mixture was filtered and the catalyst washed with
CH2Cl2 (20 mL). The organic solution was washed
successively with satd aq NaHCO3 (5×20 mL) and
water (3×20 mL), dried and evaporated. Chromato-
graphically homogenous 4 (0.67 g, 90%) was thus ob-
tained as a white solid. Recrystallization from MeOH
afforded an analytical sample 4: mp 102–103 °C; [h]D
−65.7° (c 1.04, CHCl3); wmax (KBr): 1735, 1600, 1360,
1200–1185 cm−1; 1H NMR (CDCl3): l 1.32–1.75 (m, 6
H, 3×CH2), 2.30 (t, 2 H, CH2CO2Me), 2.38 (s, 3 H,
MeC6H4SO2), 3.66 (s, 3 H, CO2Me), 3.70 (dd, 1 H,
J5a,5b 10.5, J4,5a 3 Hz, H-5a), 4.04 (ddd, 1 H, J1a%,2 7.2,
J1b%,2 5.1, J2,3 3.5 Hz, H-2), 4.32 (dd, 1 H, J4,5b 5.2 Hz,
H-5b), 5.05 (dd, 1 H, J3,4 1.5 Hz, H-3), 5.29 (ddd, 1 H,
H-4), 7.28–7.98 (m, 9 H, C6H5CO and MeC6H4SO2);
13C NMR (CDCl3): l 21.73 (MeC6H4SO2), 24.95, 25.67
and 28.26 (3×CH2), 33.99 (CH2CO2Me), 51.62
(CO2Me), 71.22 (C-5), 78.00 (C-4), 80.19 (C-2), 83.33
(C-3), 127.92, 128.18, 128.45, 129.71, 129.95 and 133.45
(aromatic), 165.14 (PhCꢀO), 174.05 (CO2Me); FABMS:
m/z 499 [MNa+], 477 [MH+]. Anal. Calcd for
C24H28O8S: C, 60.50; H, 5.91; S, 6.72. Found: C, 60.77;
H, 6.03; S, 6.39.
1. Experimental
General methods.—Melting points were determined
on a Bu¨chi 510 apparatus and were not corrected.
Optical rotations were measured on a Polamat A
(Carl–Zeiss, Jena) polarimeter at rt. IR spectra were
recorded with a Specord 75IR spectrophotometer and
band positions (wmax) are given in cm−1. NMR spectra
were recorded on a Bruker AC 250 E instrument and
chemical shifts are expressed in ppm downfield from
tetramethylsilane. Mass spectra were recorded on
Finnigan-MAT 8230 (CI), VG AutoSpec (FAB) and
Micromass LCT KA111 (ES+) mass spectrometers.
TLC was performed on DC Alufolien Kieselgel 60 F254
(E. Merck). Short-column chromatography was carried
out using Kieselgel 60 (under 0.063 mm; E. Merck).
Typical sample/adsorbent ratio was 1:30. Flash-column
chromatography was performed using ICN silica 32–
63. All organic extracts were dried with anhyd Na2SO4.
Organic solutions were concentrated in a rotary evapo-
rator under diminished pressure at a bath temperature
below 35 °C.
2S-(4%-Methoxycarbonyl-1%-butyl)-3R-p-toluenesul-
fonyloxy-4R-benzoyloxy-tetrahydrofuran (4).—A sus-
pension of 1 (2.12 g, 4.88 mmol) in a mixture of
trifluoroacetic acid (20 mL) and 6 M HCl (2 mL) was
kept at rt for 12 h. The mixture was concentrated to
one third of the initial volume, treated with satd aq
NaHCO3 (to pH 9), and extracted with CH2Cl2. The
extract was washed successively with satd aq NaHCO3
and water, dried and evaporated. Column chromatog-
raphy (PhMe) of the residue gave pure 2 (1.2 g, 60%) as
a pale yellow oil: [h]D −76.04° (c 0.89, CHCl3); wmax
(film): 3480, 1730, 1600, 1370, 1195 cm−1. To a solu-
tion of 2 (1.17 g, 2.86 mmol) in CH2Cl2 (25 mL) was
2S-(4%-Methoxycarbonyl-1%-butyl)-3S,4R-dihydroxy-
tetrahydrofuran (6).—To a solution of 4 (0.50 g, 1.05
mmol) in 95% aq N,N-dimethylformamide (20 mL, 5%
of water) was added CaCO3 (0.33 g, 3.3 mmol). The
mixture was stirred for 10 h at 150 °C, then concen-
trated in vacuo, and the remaining residue was ex-
tracted with boiling CH2Cl2 (20 mL). The suspension
was filtered and evaporated to a brown syrup. Short-
column chromatography (9:1 toluene–EtOAc) of the
residue gave oily 5 (0.22 g, 65%): [h]D −47.8° (c 1.17,
CHCl3); wmax (film): 3430, 1720–1710 cm−1. To a solu-
tion of 5 (0.20 g, 0.62 mmol) in dry MeOH (1 mL) was
added the solution of 0.1 M NaOMe in MeOH (0.4
mL). The mixture was stirred for 1 h at rt, then
acidified with glacial AcOH (to pH 5) and evaporated
by co-distillation with toluene (30 mL). The remaining
oily residue (0.16 g) was purified by short-column chro-
matography (4:1 toluene–Me2CO) to afford pure 6
(0.11 g; 81%) as a colorless syrup: [h]D −37.6° (c 0.95,
;
CHCl3); wmax (film): 3380, 1730 cm−1 1H NMR
added
a
solution of (3-methoxycarbonyl-2-pro-
(CDCl3+D2O): l 1.38–1.65 (m, 6 H, 3×CH2), 2.35 (t,
2 H, CH2CO2Me), 3.62 (s, 3 H, CO2Me), 3.58–3.80 (m,
3 H, H-2, H-3 and H-5a), 4.01 (dd, 1 H, J5a,5b 10, J4,5b
5 Hz, H-5b), 4.21 (m, 1 H J4,5a 4.6 Hz, H-4); 13C NMR
(CDCl3): l 24.85, 25.34 and 32.91 (3×CH2), 33.97
(CH2CO2Me), 51.65 (CO2Me), 71.01 (C-4), 72.63 (C-5),
75.84 and 82.09 (C-2 and C-3), 174.57 (CO2Me); LRMS
(CI): m/z 219 [MH+]. ES+ HRMS: Calcd for
C10H18NaO5: 241.1052. Found: m/z 241.1057 [MNa+].
penyl)triphenylphosphonium bromide9 (2.02 g, 4.58
mmol) in water (105 mL). To this mixture, a solution of
NaOH (0.19 g, 4.75 mmol) in water (11 mL) was added
dropwise while stirring for 15 min at rt. The reaction
mixture was stirred under nitrogen at rt for 1 h, and
then transferred into a separatory funnel. The organic
phase was separated, washed with water, dried and
evaporated. Column chromatography (PhMe) of the

V. Popsa6in et al. / Carbohydrate Research 337 (2002) 459–465
463
2,5-Anhydro-3,4-di-O-methanesulfonyl-
D
-ribose eth-
J1,2 4.7, J2,3 6.4 Hz, H-2), 5.36 (ddd, 1 H, J3,4 5 Hz,
H-4), 5.41 (dd, 1 H, H-3), 7.50 (dd, 1 H, J1,NH 0.9 Hz,
H-1), 8.02 (d, 1 H, J5%,6% 9.5 Hz, H-6%), 8.38 (ddd, 1 H,
J3%,5% 2.4, J5%,NH 0.6 Hz, H-5%), 9.13 (d, 1 H, H-3%), 11.30
(bs, 1 H, exchangeable with D2O, NH); FABMS: m/z
491 [MNa+], 469 [MH+]. Anal. Calcd for
C13H16N4O11S2×MeOH: C, 33.60; H, 4.03; N, 11.20;
S, 12.81. Found: C, 33.90; H, 3.85; N, 10.83; S, 13.20.
2S-(4%-Methoxycarbonyl-1%-butyl)-3S,4R-dimethane-
sulfonyloxy-tetrahydrofuran (7).—(a) To a stirred and
cooled solution (−10 °C) of 6 (0.103 g, 0.47 mmol) in
dry CH2Cl2 (5 mL) was added Et3N (0.20 mL, 1.44
mmol) and MsCl (0.08 mL, 1.03 mmol). Stirring was
continued for 0.5 h and the mixture diluted with
CH2Cl2 (10 mL), washed successively with aq 5% HCl
(2×10 mL), satd aq NaHCO3 (10 mL) and water (10
mL). The organic solution was dried and evaporated to
ylene acetal (10).—To a solution of 1 (2.00 g, 4.60
mmol) in 95% aq N,N-dimethylformamide (20 mL, 5%
of water) was added CaCO3 (1.00 g, 9.99 mmol), and
the mixture was stirred for 4 h at 150 °C. Examination
of the reaction mixture by TLC (4:1 toluene–Me2CO)
proved a complete conversion of 1 into 8. To the
reaction mixture was then added 10% KOH in MeOH
(6 mL) and the resulting mixture was stirred at 60 °C
for 30 min, whereupon the intermediate 8 was fully
converted to the diol 9 as established by TLC (3:2
toluene–Me2CO). The mixture was concentrated under
diminished pressure and dried by co-distillation with
1:1 toluene–EtOH (4×30 mL). The crude residue was
dissolved in dry pyridine (15 mL) and treated with
MsCl (2 mL). The mixture was stored for 24 h at rt,
then poured onto ice (100 g), acidified with 6 M aq HCl
(100 mL) and extracted with CH2Cl2 (3×30 mL). The
combined extracts were washed with water, dried and
evaporated. Short-column chromatography (CH2Cl2) of
the residue gave pure 10 (0.98 g, 64% form 1) as a white
solid. Recrystallization from EtOH gave an analytical
sample 10 as needles: mp 108–109 °C, lit.7 107–108 °C;
[h]D −46.5° (c 0.77, CHCl3); wmax (KBr): 1370–1330,
a
yellow syrup. Flash-column chromatography
(CH2Cl2) of the residue gave pure 7 (0.1615 g, 91%) as
a white solid, which upon crystallization from EtOH
gave colorless needles, mp 70–71 °C.
(b) A solution of 10 (1.00 g, 3.01 mmol) in trifl-
uoroacetic acid (10 mL) and 6 M aq HCl (1 mL) was
kept at rt for 24 h. The solution was concentrated
under diminished pressure and traces of acids were
removed by co-distillation with toluene (25 mL). To a
solution of remaining crude 11 in dry CH2Cl2 (20 mL)
was added a solution of (3-methoxycarbonyl-2-pro-
penyl)triphenylphosphonium bromide9 (2.02 g, 4.58
mmol) in water (11 mL) and to thus prepared mixture
was added a solution of NaOH (0.19 g, 4.75 mmol) in
water (11 mL). The reaction mixture was stirred at rt
for 45 min, and then transferred to a separatory funnel.
The aqueous phase was separated and the organic layer
was washed with water (50 mL), dried and evaporated.
Short-column chromatography (CH2Cl2) of the residue
(2.45 g) gave pure 13 (0.68 g, 61% from 10) as a
bright-yellow syrup: [h]D −37.5° (c 1.52, CHCl3); wmax
(film): 1725, 1660, 1630, 1370, 1190 cm−1. A solution
of 13 (0.5374 g, 1.45 mmol) in glacial AcOH (3 mL)
was hydrogenated over PtO2 (0.05 g, 0.22 mmol) at rt
for 18 h. The suspension was filtered and the catalyst
washed with CH2Cl2 (15 mL). The combined organic
solution was washed with satd aq NaHCO3 (2×20
mL), dried and evaporated to give chromatographically
homogenous 7 (0.4841 g, 89%) as a white solid. Recrys-
tallization from EtOH gave an analytical sample 7 as
colorless needles: mp 68–69 °C; [h]D −62.6° (c 1.06,
1
1180–1170 cm−1; H NMR (CDCl3): l 3.12 and 3.13
(2×s, each 3 H, 2×MeSO2), 3.88–4.28 (m, 7 H,
2×CH2-dioxolane, 2×H-5 and H-2), 5.05 (d, 1 H, J1,2
2.5 Hz, H-1), 5.15–5.28 (m, 2 H, H-3 and H-4); 13C
NMR (CDCl3): l 38.55 and 38.65 (2×MeSO2), 65.40
and 65.65 (2×CH2-dioxolane), 70.48 (C-5), 76.28 (C-
4), 76.34 (C-3), 80.98 (C-2), 102.06 (C-1).
2,5-Anhydro-3,4-di-O-methanesulfonyl-D-ribose 2%,4%-
dinitrophenylhydrazone (12).—A solution of 2,5-anhy-
dro derivative 10 (0.66 g, 1.99 mmol) in a mixture of
trifluoroacetic acid (10 mL) and concd HCl (1 mL) was
kept at rt for 24 h. The solvent was evaporated and
traces of acids were removed by co-distillation with
toluene (3×30 mL). The remaining brown oil was
purified by short-column chromatography (4:1 tolu-
ene–Me2CO) whereupon pure 11 (0.38 g, 62.5%) was
obtained as an unstable colorless syrup: [h]D −46.8° (c
0.65, CHCl3); wmax (film): 3560, 1380–1360, 1180 cm−1
.
To a solution of compound 11 (0.10 g, 0.33 mmol) in
MeOH (2 mL) was added a freshly prepared solution of
2,4-dinitrophenylhydrazine hydrochloride (0.25 g, 1.07
mmol) in MeOH (5 mL) and concd H2SO4 (0.5 mL).
The reaction mixture was stirred at rt for 0.5 h. The
separated yellow precipitate was filtered, washed with
cold MeOH and recrystallized from MeOH, to afford
pure 12 (0.11 g, 72%) as yellow needles. Short-column
chromatography (7:3 toluene–Me2CO) followed by re-
crystallization from MeOH, gave an analytical sample
12: mp 137–138 °C; wmax (KBr): 3280, 1595, 1510,
1
CHCl3); wmax (KBr): 1745, 1350, 1180 cm−1; H NMR
(CDCl3): l 1.35–1.87 (m, 6 H, 3×CH2), 2.34 (t, 1 H,
CH2CO2Me), 3.13 and 3.15 (2×s, each 3 H, 2×
MeSO2), 3.67 (s, 3 H, CO2Me), 3.99 (dt, 1 H, J2,3
=
J1a%,2=7.2, J1b%,2 4.2 Hz, H-2), 4.01 (dd, 1 H, J5a,5b 11,
1
1360–1320, 1175 cm−1; H NMR (CDCl3): l 3.18 (s, 6
J4,5a 3.8 Hz, H-5a), 4.28 (dd, 1 H, J4,5b 5.2 Hz, H-5b),
4.70 (dd, 1 H, J3,4 5.2 Hz, H-3), 5.17 (dt, 1 H, H-4); 13C
NMR (CDCl3): l 24.60, 24.80 and 31.91 (3×CH2),
H, 2×MeSO2), 4.21 (dd, 1 H, J5a,5b 11.1, J4,5a 3 Hz,
H-5a), 4.33 (dd, 1 H, J4,5b 4.5 Hz, H-5b), 4.81 (dd, 1 H,

464
V. Popsa6in et al. / Carbohydrate Research 337 (2002) 459–465
33.74 (CH2CO2Me), 38.58 (MeSO2), 51.36 (CO2Me),
70.36 (C-5), 76.15 (C-4), 78.60 (C-2), 79.43 (C-3),
173.71 (CO2Me). Anal. Calcd for C12H22O9S2: C, 38.49;
H, 5.92; S, 17.13. Found: C, 38.39; H, 6.06; S, 17.34.
2S-(4%-Methoxycarbonyl-1%-butyl)-4S-azido-3R-me-
thanesulfonyloxy-tetrahydrofuran (14).—To a solution
of 7 (0.2231 g, 0.6 mmol) in HMPA (4 mL) was added
NaN3 (0.4582 g, 7.05 mmol). The mixture was stirred at
80 °C for 5 h, then poured into cold water (50 mL) and
extracted with 1:1 benzene–hexane (3×20 mL). The
extract was washed with water, dried and evaporated to
give crude 14 (0.2289 g) as a yellow oil. Short-column
chromatography (9:1 toluene–EtOAc) of the residue
afforded pure 14 (0.1356 g, 71%) as a colorless syrup:
[h]D +18.7° (c 1.63, CHCl3); wmax (film): 2100, 1735,
NMR (CDCl3): l 1.35–1.64 (m, 6 H, 3×CH2), 1.97
and 2.06 (2×s, each 3 H, 2×MeCONH), 2.31 (t, 2 H,
CH2CO2Me), 3.58 (dd, 1 H, J5a,5b 9.2, J4,5a 6.6 Hz,
H-5a), 3.66 (CO2Me), 3.82 (ddd, 1 H, J1a,2 6.9, J1b,2 6,
J2,3 3.9 Hz, H-2), 4.05 (dd, 1 H, J4,5b 8.1 Hz, H-5b),
4.55 (ddd, 1 H, J3,NH 9, J3,4 6.1 Hz, H-3), 4.62 (m, 1 H,
J4,NH 7 Hz, H-4), 6.71 (bs, 2 H, D2O exchangeable,
2×NH); 13C NMR (CDCl3): l 22.27 (2×MeCONH),
24.29, 24.99 and 28.76 (3×CH2), 33.23 (CH2CO2Me),
50.69 (CO2Me), 51.09 (C-4), 52.11 (C-3), 69.00 (C-5),
80.36 (C-2), 169.85 and 170.27 (2×MeCONH), 173.19
(CO2Me); FABMS: m/z 323 [MNa+], 301 [MH+].
Anal. Calcd for C14H24N2O5: C, 55.98; H, 8.05; N, 9.33.
Found: C, 55.64; H, 8.00; N, 9.71.
(+)-Oxybiotin (18).—(a) To a solution of 15 (0.1860
g, 0.69 mmol) in dry THF (5 mL) was added Ph3P
(0.4550 g, 1.73 mmol) and benzyl chloroformate (0.3
mL of 50% solution in toluene, 1.19 mmol). The mix-
ture was stirred at rt for 5 h, and then treated with
concd aq NH4OH (0.5 mL) while stirring at rt for the
additional 18 h. The mixture was evaporated, and the
residue partitioned between water (10 mL) and CH2Cl2
(5 mL). The aqueous solution was washed with CH2Cl2
(5 mL) to remove the Ph3PO and concentrated by
co-distillation with 1:1 toluene–EtOH (2×20 mL).
Flash chromatography (9:1 EtOAc–MeOH) of the
residue gave pure methyl ester 17 (0.040 g, 24%).
(b) A solution of 15 (0.1 g, 0.37 mmol) in dry CH2Cl2
(6 mL) was hydrogenated over PtO2 (0.03 g, 0.13
mmol) for 6 h at rt, and then to the stirred and cooled
(0 °C) mixture was added Et3N (0.1 mL, 0.87 mmol) in
one portion. A solution of triphosgene (0.054 g, 0.19
mmol) in dry CH2Cl2 (3 mL) was added dropwise while
stirring the mixture at 0 °C for 1 h. After stirring at rt
for additional 18 h, the suspension was filtered and the
catalyst washed with CH2Cl2. The combined organic
solution was concentrated and the residue purified by
flash chromatography (9:1 EtOAc–MeOH) to afford
pure 17 (0.061 g, 68%) as a colorless solid: wmax (KBr):
1
1360, 1180 cm−1; H NMR (CDCl3): l 1.38–1.82 (m, 6
H, 3×CH2), 2.34 (t, 2 H, CH2CO2Me), 3.09 (s, 3 H,
MeSO2), 3.66 (s, 3 H, CO2Me), 3.89 (ddd, 1 H, J2,3 4.2,
J1a%,2 5.5, J1b%,2 7.5 Hz, H-2), 3.94 (dd, 1 H, J5a,5b 10.2,
J4,5a 2.5 Hz, H-5a), 4.02 (dd, 1 H, J4,5b 4.5 Hz, H-5b),
4.20 (ddd, 1 H, J3,4 2 Hz, H-4), 4.66 (dd, 1 H, H-3); 13C
NMR (CDCl3): l 24.55, 25.14 and 31.91 (3×CH2),
33.77 (CH2CO2Me), 38.54 (MeSO2), 51.36 (CO2Me),
65.78 (C-4), 70.25 (C-5), 83.18 (C-2), 86.19 (C-3),
174.00 (CO2Me); FABMS: m/z 322 [MH+]. ES+
HRMS: Calcd for C11H20N3O6S: 322.1073. Found: m/z
322.1079 [MH+].
2S - (4% - Methoxycarbonyl - 1% - butyl) - 3S,4R - diaceta-
mido-tetrahydrofuran (16).—To a solution of 7 (0.1605
g, 0.43 mmol) in DMF (10 mL) was added NaN3
(0.3890 g, 5.98 mmol) and NH4Cl (0.0320 g, 0.6 mmol).
The mixture was stirred at 150 °C for 20 h, and then
evaporated under diminished pressure. Flash-column
chromatography of the residue (4:1 light petroleum–
EtOAc) gave pure 15 (0.0430 g, 37.4%) as colorless oil.
Further elution afforded pure 14 (0.036 g, 26%). Com-
pound 14 was dissolved in DMF (3.5 mL), and to the
solution was added NaN3 (0.0736 g, 1.13 mmol) and
NH4Cl (0.0064 g, 0.12 mmol). The mixture was stirred
at 150 °C for 24 h. After the workup as described
above, and flash purification on a column of silica, an
additional amount of pure 15 (0.0112 g) was obtained.
Total yield: 0.0542 g (47%) of 15: [h]D +35.5° (c 1.79,
CHCl3); wmax (film): 2100, 1740 cm−1; LRMS (CI): m/z
269 [MH+]. A solution of 15 (0.1214 g, 0.54 mmol) in
glacial AcOH (3 mL) and Ac2O (3 mL) was hydro-
genated over PtO2 (0.04 g, 0.18 mmol) at rt for 23 h.
The suspension was filtered and the catalyst washed
with CHCl3 (20 mL) and MeOH (10 mL). The com-
bined filtrates were concentrated and residual AcOH
removed by co-distillation with a 1:2 mixture of tolu-
ene–MeOH (4×15 mL), whereupon crude 16 re-
mained as a white solid. Recrystallization from a
mixture of CH2Cl2–hexane gave an analytical sample
16 (0.1160 g, 85%): mp 151–152 °C; [h]D +8.8° (c 1.17,
3410–3120, 1750, 1710 cm−1
;
1H NMR (CDCl3); l
H,
1.21–1.80 (m, H, 3×CH2), 2.32 (t,
6
2
CH2CO2Me), 3.40 (m, 1 H, J2,3 3.6, J1%,2 6.4 Hz, H-2),
3.49 (dd, 1 H, J5a,5b 10.1, J4,5a 4.2 Hz, H-5a), 3.63 (s, 3
H, CO2Me), 3.86 (d, 1 H, H-5b), 4.17 (dd, 1 H, J3,4 8.4
Hz, H-3), 4.34 (dd, 1 H, H-4), 5.98 and 6.18 (2×bs,
each 1 H, 2×NH); 13C NMR (CDCl3): l 24.81, 25.52
and 28.36 (3×CH2), 33.67 (CH2CO2Me), 51.42
(CO2Me), 57.52 (C-4), 58.98 (C-3), 75.23 (C-5), 82.58
(C-2), 163.62 (NHCONH), 174.14 (CO2Me). To a solu-
tion of 17 (0.0550 g, 0.23 mmol) in water (1.5 mL) was
added Ba(OH)2×8 H2O (0.080 g, 0.25 mmol). The
mixture was stirred at 100 °C for 1.5 h, then acidified to
Congo red with 1 M H2SO4, and then centrifuged to
remove BaSO4. The solution was concentrated by co-
distillation with 1:1 toluene–MeOH to afford pure 18
(0.0517 g, 98%) as a white powder. Recrystallization
1
CHCl2); wmax (KBr): 3290–3080, 1730, 1550 cm−1; H

V. Popsa6in et al. / Carbohydrate Research 337 (2002) 459–465
465
2. Hofmann, K. J. Am. Chem. Soc. 1945, 67, 1549–
1562.
3. Dyke, S. F. In Chemistry of Natural Products; Bentley,
K. W., Ed.; Interscience: London, 1964; Vol. 6, pp.
161–181.
4. Ohrui, H.; Kuzuhara, H.; Emoto, S. Agric. Biol. Chem.
1971, 35, 752–755.
5. Defaye, J. Ad6. Carbohydr. Chem. Biochem. 1970, 25,
from water gave pure 18 as silky needles: mp 187–188 °C,
lit.4 187–188 °C; [h]D +57.8° (c 0.65, 1 M aq NaOH);
lit.4 +57.7°; 1H NMR (Me2SO-d6): l 1.18–1.58 (m, 6 H,
3×CH2), 2.20 (t, 2 H, CH2CO2Me), 3.33 (m, 1 H, J2,3
4 Hz, H-2), 3.39 (dd, 1 H, J5a,5b 9.8, J4,5a 4.6 Hz, H-5a),
3.65 (d, 1 H, H-5b), 4.07 (dd, 1 H, J3,4 8.7 Hz, H-3), 4.21
(dd, 1 H, H-4), 6.36 and 6.40 (2×bs, 1 H each, 2×NH);
13C NMR (Me2SO-d6): l 25.29, 25.99 and 28.83 (3×
CH2), 34.35 (CH2CO2Me), 57.53 (C-4), 59.01 (C-3), 74.34
(C-5), 82.85 (C-2), 163.80 (NHCONH), 176.09 (CO2H).
181–228.
6. Miljkovic´, D.; Popsavin, V.; Hranisavljevic´, J. Bull. Soc.
Chim. Beograd. 1983, 48, 211–218.
7. Miljkovic´, D.; Popsavin, V.; Slavica, B. Bull. Soc. Chim.
Beograd. 1983, 48, 219–227.
8. Defaye, J.; Hildesheim, J. Tetrahedron Lett. 1968, 3,
313–317.
Acknowledgements
9. Buchta, E.; Andree, F. Chem. Ber. 1959, 92, 3111–3115.
10. Miljkovic´, D.; Popsavin, V.; Harangi, J.; Batta, Dy. J.
Serb. Chem. Soc. 1989, 54, 163–165.
11. Ohrui, H.; Emoto, S. Tetrahedron Lett. 1975, 32, 2765–
2766.
This work was supported by a research grant from the
Ministry of Science, Technologies and Development of
the Republic of Serbia. The authors are grateful to Mrs
T. Marinko-Covell (University of Leeds, UK) and to Mr
D. Djokovic´ (Faculty of Chemistry, University of Bel-
grade, Yugoslavia), for recording the mass spectra.
12. Golobov, Y. G.; Kasukhin, L. F. Tetrahedron 1992, 48,
1459–1462.
13. Ariza, X.; Urp´ı, F.; Vilarrasa, J. Tetrahedron Lett. 1999,
40, 7515–7517.
14. Ariza, X.; Pineda, O.; Urp´ı, F.; Vilarrasa, J. Tetrahedron
Lett. 2001, 42, 4995–4999 and references therein.
15. Eckert, H.; Foster, B. Angew. Chem., Int. Ed. Engl. 1987,
26, 894–895.
16. Miljkovic´, D.; Velimirovic´, S.; Csana´di, J.; Popsavin, V.
J. Carbohydr. Chem. 1989, 8, 457–467.
References
1. Miljkovic´, D.; Popsavin, V.; Harangi, J. Tetrahedron
Lett. 1987, 28, 5733–5736.