Zemplen deacetylation

Glycosides may also be prepared by enzyme-catalyzed condensation reactions utilizing a glycosyl fluoride. Thus 6-0-a-maltosylcyclodextrins were prepared enzymically from a-maltosyl fluoride (obtained from the corresponding heptaacetate by Zemplen deacetylation) and cyclodex-trins. " ... 

The methyl ester 107 was obtained by treatment of ammonium KDO with methanol in the presence of an acidic catalyst,79 and it is likely that these esterification conditions (rather than the presence of the ester group of itself) favor the furanoid form. It would be of interest to ascertain whether the methyl ester (111) of KDO, when prepared by Zemplen deacetylation of 70 (see Scheme 31), would also yield furanoid derivatives upon benzoylation with benzoyl chloride in pyridine. 

A mixture of triacetyl-a-D-fructofuranoside (1521, a, R2 = OMe) and triacetyl-jS-D-fructopyranoside (1523, R1 = Me) was obtained when the crude glycoside mixture obtained in the glucosidation of 1448 in methanol containing 1% hydrogen chloride at room temperature for 5 hr was ace-tylated with acetic anhydride in the presence of pyridine a 0°C for 3 days (86MI10). The Zemplen deacetylation of 1521 (R2 = OMe) was carried out in quantitative yield. 

The same intermediate 67 was also prepared" from methyl D-fmctofnranoside (68), prepared from D-fructose (Scheme 13), by reaction with 2,4,6-triisopropylbenzensulfonyl chloride in pyridine, followed by acetylation and snbseqnent Sn2 displacement of the sulfonyloxy group with azide ion to afford methyl l,3,4-tri-0-acetyl-6-azido-6-deoxy-D-fructofuranoside (69) in 50% overall yield from D-fmctose. Zemplen deacetylation of 69 followed by acid hydrolysis afforded 6-azido-6-deoxy-D-fmctose (67) in 82% yield, which underwent catalytic hydrogenation to fnmish 2 in 25% overall yield from D-fructofuranose. 

C-5-OH group of 24 afforded the divergent intermediate 25 in quantitative yield. The triflate 25 underwent Sn2 displacement with sodium azide to give the 5-azido-L-altrofuranoside 26, which subsequently treated with sodium methoxide in methanol followed by hydrogenation to afford 1,5-dideoxy- 1,5-imino-L-altritol (27) in 77% overall yield from 24. Inversion of the configuration at C-5 in 25 was achieved by treatment with sodium nitrite in DMF, followed by trifiation of the resulting L-altro derivative to afford the triflate 28. Treatment of 28 with sodium azide in DMF followed by Zemplen deacetylation afforded the azide 29, which on hydrogenation afforded 4 in 40% overall yield from 24. 

Hepta-O-acetyl-a-kojibiosyl bromide has been converted into the j3-chloride form by treatment with tetraethylammonium chloride, and then condensed immediately with benzyl 2,3,4-tri-0-benzyl-j3-D-glucopyranoside in an AgCl04-Ag2C03 catalysed reaction.0-a-D-Glucopyranosyl-(l2)-0-a-D-gluco-pyranosyl-(l 6)-D-glucose was obtained on hydrogenolysis and Zemplen deacetylation. 

AC2 Introduction does not require amino deprotection removal by Zemplen deacetylation Primary alcohols... 

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