engleski

Synthesis, Intramolecular Migrations and Enzymic Hydrolysis of Partially Pivaloylated Methyl alpha- D-Mannopyranosides

Acid or base catalyzed intramolecular migratios of acyls in sugar molecules are well known, and the possible mechanism of these transesterifications has been described.(1) Pivaloyl group migration caused by enzymes present in some mammalian sera was previously described in dipivaloylated glucose.(2) A series of methyl O-pivaloyl-alpha-D- mannopyranosides was synthesized using pivaloyl chloride in pyridine. The 3, 6-di-O-pivaloyl derivative 6 undergoes intramolecular transesterification in neutral conditions (buffer, pH 7.2) to give its 2, 6-di-O-pivaloyl analogue 5. The course of this migration was followed using 14C-labelled 6. As opposed to 6 compound 5 was shovn to be good substrate for esterases present in rabbit serum. Thus, regioselective enzymic hydrolysis led to the preferential cleavage of the 2-O-Piv group to yield a mixtute of 2- and 6-O- monopivalates, 3 and 4, in ratio of 1:2.6.

O-pivaloyl derivatives of mannose ; rabbit serum ; intramolecular migrations

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