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Glycosylidene Carbenes. Part 25. Glycosidation of ginkgolides B and A
Author(s) -
Weber Martin,
Vasetla Andrea
Publication year - 1997
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19970800808
Subject(s) - chemistry , anomer , stereoselectivity , diazirine , glucoside , regioselectivity , ginkgolides , stereochemistry , aldose , alcohol , catalysis , medicinal chemistry , organic chemistry , glycoside , medicine , ginkgo , alternative medicine , pathology , traditional medicine
Abstract Ginkgolide B ( 1b ) has been glucosylated in THF with the glucosylidene‐derived diazirine 2 under thermal or photochemical conditions. Depending on the amount of 2 , we obtained either monoglucosides ( 5 – 8 ), diglucosides ( 13 – 17 ), or triglucosides ( 21 – 23 ). In keeping with earlier results, the use of THF as solvent led mostly to β‐ D ‐glucosides. The modest regioselectivity in the formation of the monoglucosides, glucosylated either at OC(1) or OC(10), is rationalized on the basis of the relative kinetic acidity of the intra‐ and intermolecularly H‐bonded OH groups of 1b . The tertiary HOC(3) of the monoglucosides was more readily glucosylated than the secondary HOC(1) or HOC(10) (H‐bonded). Glucosidation with 3.5 equiv. of 2 led to triglucosides, with the tri‐β‐ D ‐glucoside 21 (42%) as the major product. Catalytic hydrogenation afforded the free glucosides 9 – 12 , 18 – 20 , and 24 . The di‐ and triglucosides are readily soluble in H 2 O. Glucosidation with 2 of the ginkgolide‐A‐derived tertiary alcohol 25 yielded 93% of the β‐ D ‐anomeric glucoside 26 . Similarly, glycosidation of 25 with the lactosylidene‐derived diazirine 34 proceeded with a very high stereoselectivity, yielding 92% of the β‐ D ‐lactoside 35 , that was deprotected to the H 2 O soluble acetate 36 .