GALACTURONIC ACID-DERIVATIVES .9. REGIOSELECTIVE ENZYMATIC ACETYL ESTER HYDROLYSIS OF D-GALACTURONIC ACID-DERIVATIVES AND RELATED REACTIONS

A number of D-galacturonic acid derivatives (1, 3, 7 and 9) have been selectively deacetylated in enzyme-catalyzed reactions. The 2-O-acetyl groups were selectively hydrolyzed from -tri-O-acetyl-beta-D-galactop yranurono-6,1-lactone (1), and methyl [methyl (3) and benzyl (7) 3,4-t ri-O-acetyl-beta-D-galactopyranosid]uronates, affording the specifical ly deacetylated products in good to excellent yields. The methyl 1,2,3 ,4-tetra-O-acetyl-alpha-D-galactopyranuronate (9) was hydrolyzed at th e anomeric position in 48% yield using the acylase from Aspergillus me lleus (E-1), whereas the lipases from wheat germ (E-5 and E-7) catalyz ed the selective cleavage of the acetyl groups in both the 1- and 2-O- positions, furnishing the methyl 3,4-di-O-acetyl-D-galactopyranuronate (12) in 46% isolated yield. The latter compound was obtained in nearl y quantitative yield by selective enzymatic deacetylation at the 2-O-p osition of 7, followed by hydrogenolytic cleavage of the anomeric O-be nzyl group. Isopropylidenation of 12 furnished the hitherto unknown me thyl l-1,2-O-isopropylidene-alpha-D-galactopyranuronate (13).