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Reactions of Partially Acylated Aldohexopyranosides, VIII. A New Synthesis of the Tetradeoxydisaccharide in Avermectins
Author(s) -
Rainer Hildegard,
Scharf HansDieter,
Runsink Jan
Publication year - 1992
Publication title -
liebigs annalen der chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 0170-2041
DOI - 10.1002/jlac.199219920121
Subject(s) - chemistry , yield (engineering) , trifluoromethanesulfonate , trimethylsilyl trifluoromethanesulfonate , glycosyl , disaccharide , trimethylsilyl , medicinal chemistry , glycosyl donor , rhamnose , stereochemistry , glycosylation , methyl group , organic chemistry , polysaccharide , catalysis , group (periodic table) , biochemistry , materials science , metallurgy
Methyl 4‐ O ‐benzyl‐3‐ O ‐methyl‐2‐ O ‐pivaloyl‐α‐ L ‐rhamnopyranoside ( 6 ) was prepared from L ‐rhamnose in an improved synthesis in six steps (overall yield: 51%) and was used as the key building block. Acetolysis of 6 gave the glycosyl donor, 1,4‐di‐ O ‐acetyl‐3‐ O ‐methyl‐2‐ O ‐pivaloyl‐α‐ L ‐rhamnopyranose ( 7 ), which was coupled with the acceptor, methyl 3‐ O ‐methyl‐2‐ O ‐pivaloyl‐α‐ L ‐rhamnopyranoside ( 8 ), simply prepared by debenzylation of 6 . The glycosylation reaction was carried out in the presence of trimethylsilyl triflate and led exclusively to the α‐linked disaccharide, methyl 4‐ O ‐(4‐ O ‐acetyl‐3‐ O ‐methyl‐2‐ O ‐pivaloyl‐α‐ L ‐rhamnopyranosyl)‐3‐ O ‐methyl‐2‐ O ‐pivaloyl‐α‐ L ‐rhamnopyranoside ( 9 ). Selective removal of the acetate group and irradiation of the 2,2′‐dipivaloates gave directly the tetradeoxydisaccharide, methyl 4‐ O ‐(α‐ L ‐oleandrosyl)‐α‐ L ‐oleandropyranoside ( 11 ). Irradiation of compound 8 afforded methyl α‐ L ‐oleandropyranoside ( 11 ). Irradiation of compound 8 afforded methyl α‐ L ‐oleandropyranoside ( 12 ) as the only product in 80% yield.