Design and studies towards the bisubstrate analogs as potential inhibitors of glycosyltransferase GnT-V

Bisubstrate analogs have been designed as potential inhibitors of N-acetylglycosaminyltransferase V (GnT-V), an enzyme that controls the biosynthesis of the complex carbohydrates of cell-surface glycoconjugates. These bisubstrate analogs are different from either donor- or acceptor-like inhibitors. They are designed to mimic the transition-state nature of both the donor and the acceptor substrates that are involved in enzymatic glycosylation reaction. Our approach includes: (1) the hydroxylamine-connection of the glycosyl donor substrate and the acceptor substrate; (2) the use of carbon-phosphor bonds instead of oxygenphosphor bonds for stable phosphate mimics; (3) the conversion of donor substrates to polyhydroxylated pyrrolidines or piperidines which resemble the common structures in naturally-occurring iminosugar glycosidase inhibitors.; Two practical methods have been developed towards the synthesis of the bisubstrate analogs as potential inhibitors of GnT-V. The key feature of the first method is the use of intramolecular Michael addition reaction. The intramolecular Michael addition of N-alkoxyamines to alpha,beta-unsaturated phosphonates has successfully produced N-alkoxy polyhydroxylated pyrrolidine phosphonates and N-alkoxy polyhydroxylated piperidine phosphonates under mild conditions. Meanwhile, a series of oxazidine compounds were synthesized as the application of intramolecular Michael addition reaction of N-alkoxyamines.; The second method has been developed for the preparation of the sugar portion in bisubstrate analogs. N-Phenyl diethyl glycosylphosphorimidates have been proved to be effective glycosyl donors in the glycosidation reactions. These glycosyl donors have shown double function for the glycosylation reactions. Under the glycosidation conditions of LPTS/Bu4NI in benzene at 40°C, alpha-glycosides were obtained as the major products, whereas beta-glycosides were formed predominantly when promoted by TMSOTf in propionitrile at -78°C. In addition, 2-deoxy glycosyl phosphorimidites have shown to be efficient glycosyl donors for the formation of 2-deoxyglycosides. 2-Deoxy-alpha-glycosides were successfully obtained in the presence of TMSOTf in propionitril at -78°C, even in the cases of hindered acceptor alcohols.