New synthetic trisaccharide inhibitors for N-acetylglucosaminyltransferase-V

The trisaccharide octyl 2-acetamido-2-deoxy-beta-D-glucopyranosyl -(1-->2)-alpha-D-mannopyranosyl-(1-->6)-beta-D-glucopyranoside (5) is an acceptor substrate for N-acetylglucosaminyltransferase-V (EC 2.4.1.155) which adds a beta-GlcNAc residue to OH-6 of the central Man-residue. In the present work, 10 analogues of 5, each missing the potentially reactive OH-6 group, were chemically synthesized. The key intermediate used was octyl 2-acetamido-2-deoxy-beta-D-glucopyranosyl-(1-->2)-6-amino-6-deoxy-4-O -methyl-alpha-D-mannopyranosyl-(1-->6)-beta-D-glucopyranoside (6a), which was synthesized in stepwise fashion by sequential coupling of protected monosaccharide residues. The 6'-amino group in 6a, was then selectively derivatized by either acylation or alkylation with hydrophobic, hydrophilic, charged, aromatic and potential covalently inactivating groups. The 10 trisaccharide analogues thus produced were evaluated for inhibition against GlcNAcT-V isolated from hamster kidney. All of the compounds were competitive inhibitors with Ki values ranging from 21 to 297 microM. These results indicate that acceptor substrate (or inhibitor)-enzyme complex does not involve critical recognition contacts at the position of transfer.