Synthesis and characterization of 2-O-beta-lactosylglycerol, 1,2-di-O-beta-lactosyl-(R,S)-glycerols, and 1,2,3,-tri-O-beta-lactosylglycerol

Flexible cyclic ethers/polyethers as novel P2-ligands for HIV-1 protease inhibitors: design, synthesis, biological evaluation, and protein-ligand X-ray studies

We report the design, synthesis, and biological evaluation of a series of novel HIV-1 protease inhibitors. The inhibitors incorporate stereochemically defined flexible cyclic ethers/polyethers as high affinity P2-ligands. Inhibitors containing small ring 1,3-dioxacycloalkanes have shown potent enzyme inhibitory and antiviral activity. Inhibitors 3d and 3h are the most active inhibitors. Inhibitor 3d maintains excellent potency against a variety of multi-PI-resistant clinical strains. Our structure-activity studies indicate that the ring size, stereochemistry, and position of oxygens are important for the observed activity. Optically active synthesis of 1,3-dioxepan-5-ol along with the syntheses of various cyclic ether and polyether ligands have been described. A protein-ligand X-ray crystal structure of 3d-bound HIV-1 protease was determined. The structure revealed that the P2-ligand makes extensive interactions including hydrogen bonding with the protease backbone in the S2-site. In addition, the P2-ligand in 3d forms a unique water-mediated interaction with the NH of Gly-48.

Synthesis of 1,2,3-tri-O-beta-lactosyl-D-threitol and 1-O-benzyl-2,3,4-tri-O-beta-lactosyl-D-threitol

The coupling of 2,3,6,2',3',4',6-hepta-O-acetyl-alpha-lactosyl bromide with 1,4-di-O-benzyl-D-threitol using mercury(II) cyanide as a promoter, with subsequent deprotection of one or both of the benzyl groups, further glycosylation, and deacetylation afforded the title compounds. This class of compound is useful in the assessment of binding properties of D-galactopyranose to human and rabbit hepatocytes.

Binding of D-galactose-terminated ligands to rabbit asialoglycoprotein receptor

The binding affinities of a series of D-galactose-terminated glycerol glycosides and oligosaccharides for the asialoglycoprotein receptor isolated from rabbit liver were determined in vitro using a radioreceptor-inhibition assay with 125I-asialoorosomucoid. The relative affinities of the synthetic ligands increased with the number of exposed D-galactose termini. Of the compounds examined, 1,2,3-tri-O-beta-lactosylglycerol associated with the greatest affinity (estimated Kd = 7.97 x 10(-5) M). Examination of the affinities of the synthetic series indicated that both the number and propinquity of the D-galactose termini influenced the strength of the binding interactions.

Synthesis and characterization of 6-O-beta-lactosyl-alpha,beta-lactoses, 1-O-(6-O-beta-lactosyl-beta-lactosyl)-(R,S)-glycerols, and 4,6-di-O-beta-D-galactopyranosyl-alpha,beta-D-glucoses

1,2,3,2',3',4',6'-Hepta-O-acetyl-beta-lactose (4) was coupled with 2,3,6,2',3',4',6'-hepta-O-acetyl-alpha-lactosyl bromide (7) in the presence of Hg(CN)2 to afford 1,2,3,2',3',4',6'-hepta-O-acetyl-6-O-(2,3,6,2',3',4',6'-hepta-O-acetyl-b eta- lactosyl)-beta-lactose (11) which, upon O-deacetylation, gave 6-O-beta-lactosyl-alpha,beta-lactoses (64% from 4). In contrast, the reaction of 7 with benzyl 2,3,2',3',4',6'-hexa-O-acetyl-beta-lactoside in the presence of Hg(CN)2 produced 3,6,2',3',4',6'-hexa-O-acetyl-1,2-O- (2,3,2',3',4',6'-hexa-O-acetyl-1-O-benzyl-beta-lactos-6-yl orthoacetyl)-alpha-lactose (63%) and 3,6,2',3',4',6'-hexa-O-acetyl-1,2-O-(1- cyanoethylidene)-alpha-lactose (27%). The glycosidation of 4 using 2,3,4,6-tetra-O-acetyl-alpha-D-galactopyranosyl bromide in the presence of Hg(CN)2 afforded, after deprotection, 4,6-di-O-beta-D-galactopyranosyl-alpha,beta-D-glucoses (66%). The reaction of 11 with 1,2-di-O-benzyl-(R,S)-glycerols and trimethylsilyl trifluoromethanesulfonate yielded, after deprotection, 1-O-(6-O-beta-lactosyl-beta-lactosyl)-(R,S)-glycerols (18%). Under the same coupling conditions 11 reacted with 2-O-benzylglycerol to form 3-O-acetyl-2-O-benzyl-1-O-[2',3',4',6'-hexa-O-acetyl-6-O-(2,3,6,2',3',4' ,6'- hepta-O-acetyl-beta-lactosyl)-beta-lactosyl]-(R,S)-glycerols (16%).

Synthesis and characterization of 6-O-beta-lactosyl-alpha,beta-D-mannopyranoses and 2,6-di-O-beta-lactosyl-alpha,beta-D-mannopyranoses

The reaction of 2,3,6,2',3',4',6'-hepta-O-acetyl-alpha-lactosyl bromide (4) and benzyl 3,4-di-O-benzyl-alpha-D-mannopyranoside (3) in the presence of mercury(II) cyanide in benzene-nitromethane produced benzyl 3,4-di-O-benzyl-2,6-bis-O-(2,3,6,2',3',4',6'-hepta-O-acetyl-beta-lact osy l)-alph a D-mannopyranoside (5) and benzyl 3,4-di-O-benzyl-6-O-(2,3,6,2',3',4',6'-hepta-O-acetyl-beta-lactosyl)-alp ha-D- mannopyranoside (6), as part of a complex mixture. Column chromatography, followed by acetylation of the fraction containing 5 and 6, gave a sample of 5 and benzyl 2-O-acetyl-3,4-di-O-benzyl-6-O (2,3,6,2',3',4',6'-hepta-O-acetyl-beta-lactosyl)-alpha-D-mannopyranoside (7) in approximately 35% and 17% yields (based on 4), respectively. Deprotection of 5 and 7 afforded the target compounds, namely 2,6-di-O-beta-lactosyl-alpha,beta-D-mannopyranoses and 6-O-beta-lactosyl-alpha,beta-D-mannopyranoses, respectively. If the coupling of 4 with 3 were performed in the presence of silver trifluoromethanesulfonate and 2,4,6-trimethylpyridine, only a mixture of 3,6,2',3',4',6'-hexa-O-acetyl- alpha-lactose-1,2-[( 3,6,2',3',4',6'-hexa-O-acetyl-alpha-lactose 1,2-(benzyl 3,4-di-O-benzyl-alpha-D-mannopyranosid-6-yl orthoacetyl)-2-yl]orthoacetate) and 3,6,2',3',4',6'-hexa-O-acetyl-alpha-lactose 1,2-(benzyl 3,4-di-O-benzyl-alpha-D-mannopyranosid-6-yl orthoacetate) was obtained. The orthoacetates were characterized by n.m.r. spectroscopy. The two target materials are useful in the assessment of the binding properties of galactose-terminated ligands to the asialoglycoprotein receptor of normal rabbit and human hepatocytes.