SYNTHESIS OF GALACTOSE-DERIVED AND N-ACETYLGLUCOSAMINE-DERIVED TETRAZOLES AND THEIR EVALUATION AS BETA-GLYCOSIDASE INHIBITORS

The title compounds 6 and 7 have been prepared from the known 2,3-di-O-benzyl-4,6-O-benzylidene-D-galactose (18) and N-2-acetyl-tri-O-benzyl-D-glucosamine oxime (29) in eight and six steps, respectively. The azidonitrile leading to the benzylated galacto-tetrazole 16 was prepared from 14 and cyclized under the conditions of its formation (Scheme 1). The alcohol 13 was obtained by oxidation of 10 followed by reduction. Better yields and diastereoselectivities were realized, when the benzylidene-protected D-galacto-alcohol 20 was subjected to oxidoreduction, yielding the L-altro-alcohol 22 via the ketone 21 (Scheme 2). Treatment of the corresponding tosylate 24 with NaN3 yielded the tetrazole 25, which was deprotected to 6. The tetrabenzyl ether 16 (from 14, or from 25 via 27) was reduced to 28 and deprotected to give the known deoxygalactostatin 8 (Scheme 2). Oxidation of the hydroxynitrile 30, derived from 29, followed by reduction of 32 yielded mostly the L-ido-hydroxynitrile (Scheme 3), which was tosylated and treated with NaN, to give the tetrazole 35a and its manno-isomer 36a, while Al(N-3)(3) yielded (E)- and (2)-38 (Scheme 4). The intermediate azide 39 was isolated besides 40 when NH4N3/DMF was used; thermolysis of 39 gave mostly 35a, which was deprotected to 7, besides some elimination product 41. Both 6 and 7 are stable in the PH range 1-10; at pH 12, 6 is unaffected but, 7 shows some epimerization to the manno-configurated isomer 43. The tetrazole 6 is a competitive inhibitor of the P-galactosidases from E. coli (K-I = 1 mu M, PH 6.8) and bovine liver (K-I = 0.8 mu M, pH 7.0); the N-acetyl-beta-D-glucosaminidase from bovine kidney is competitively inhibited by 7 (K-I approximate to 0.2 mu M, PH 4.1).