Chloroethyl Thioglycosides
1497
2-Iodoethyl 2,3,4,6-Tetra-O-acetyl-1-thio-β-D-glucopyranoside (4g)
The substance was prepared from the starting compound 4e by a procedure15 analogous to that used
for the iodo derivative 4f. The syrup was crystallized from ethanol. Yield 4.9 g (89%), m.p. 125–126 °C,
[α]D –35.8° (c 0.5, chloroform). For C16H23IO9S (521.3) calculated: 36.86% C, 4.45% H, 24.85% I,
6.15% S; found: 37.15% C, 4.69% H, 24.23% I, 6.27% S.
2-Hydroxyethyl 2,3,4,6-Tetra-O-acetyl-1-thio-β-D-galactopyranoside14 (4h)
A) Thiogalactose 3a (10.9 g, 30 mmol) in acetone (30 ml) was alkylated by agitation with 2-iodo-
ethanol (5.8 g, 33 mmol) in the presence of K2CO3 (4.14 g, 30 mmol). The reaction mixture was
treated as reported above for substances 4a–4c. The syrup obtained was chromatographed on a col-
umn of Silica Gel L 100/250 (Lachema); elution with chloroform. Yield 8.1 g (70%), crystalline so-
lidified syrup, [α]D +23° (c 0.5, chloroform). TLC (benzene–ethyl acetate 1 : 1): RF 0.25. For
C16H24O10S (408.4) calculated: 47.05% C, 5.93% H, 7.85% S; found: 47.28% C, 6.02% H, 7.62% S.
B) A gentle stream of oxirane was fed for roughly 2 h into a solution of thiogalactose 3a (7.2 g,
20 mmol) in chloroform (50 ml). After completion of the reaction (TLC, see above), the reaction
mixture was nitrogen purged and extracted consecutively with 5% sodium hydroxide (25 ml), 5%
sulfuric acid (25 ml), and water. After drying, the chloroform solution was evaporated and chroma-
tographed (see procedure A). Yield 6.7 g (88%), properties identical with those of the product pre-
pared sub A).
2-Hydroxyethyl 2,3,4,6-Tetra-O-acetyl-1-thio-β-D-glucopyranoside (4i)
A) The substance was prepared by alkylation of compound 3b (10.9 g, 30 mmol) with 2-iodoetha-
nol (5.8 g, 33 mmol) by procedure A for substance 4h above. Yield 10.5 g (86%), m.p. 70–73 °C,
[α]D –14° (c 0.5, chloroform). TLC (benzene–ethyl acetate 1 : 1): RF 0.24. For C16H24O10S (408.4)
calculated: 47.05% C, 5.93% H, 7.85% S; found: 47.32% C, 6.21% H, 7.62% S.
B) The substance was obtained by reacting compound 3b (7.2, 20 mmol) with oxirane as described
in procedure B for substance 4h above. Yield 6.6 g (87%).
Preparation of the Free Thioglycosides 5a–5c, 6a, 6b by Deacetylation after Zemplén
To a solution of acetylated thioglycoside 4a–4c, 4h, 4i (10 g) in anhydrous methanol (100 ml) was
added sodium methoxide prepared from sodium (0.1 g) and methanol (10 ml). The system was
allowed to stand for 2 h at room temperature or overnight in a refrigerator at 0 °C, during which the
deacetylation was accomplished (TLC monitoring using the benzene–acetone 4 : 1 or ethyl acetate–
2-propanol–water 9 : 4 : 2 system). Where the crystalline product failed to separate, the solution was
neutralized by adding a catex (Dowex 50 W × 8 in the H+ cycle) and evaporated to a syrup. Addi-
tional fractions were obtained from the mother liquors on crystallization from methanol.
2-Chloroethyl 1-thio-β-D-galactopyranoside (5a). M.p. 93–98 °C (decomposition), [α]D –23° (c 0.8,
water), (ref.4: m.p. 92–98 °C, [α]D –24.6° (c 0.5, water)), yield 5.5 g (91%). The product crystallizes
with an approximately equimolar amount of methanol, which can be removed by drying in a vacuum
over P2O5 at 64 °C. For C8H15ClO5S (258.7) calculated: 37.14% C, 5.84% H, 13.70% Cl, 12.39% S;
found: 37.19% C, 5.84% H, 13.81% Cl, 12.37% S.
2-Chloroethyl 1-thio-β-D-glucopyranoside (5b). Yield 5.4 g (90%) of a partly crystallized syrup,
whose purification for elemental analysis failed; [α]D –38° (c 0.7, water).
2-Chloroethyl 2-acetamido-2-deoxy-1-thio-β-D-glucopyranoside (5c). Yield 6.24 g (89%), m.p. 174–176 °C
(dec.), [α]D –34° (c 0.4, methanol). For C10H18ClNO5S (299.8) calculated: 40.06% C, 6.05% H, 11.83% Cl,
4.67% N, 10.69% S; found: 37.89% C, 6.10% H, 11.53% Cl, 4.43% N, 10.51% S.
Collect. Czech. Chem. Commun. (Vol. 61) (1996)