Biomedical subjects
Publications and source records attributed to B Korba.
Combinatorial chemistry is playing an increasingly prominent role in the process of drug discovery. A nucleic acid-based (NAB) scaffold can be engineered to create functional group and topological diversity in a library. Described herein is the parallel solid-phase synthesis of combinatorial libraries of nucleoside phosphoramidates, and the first evaluation of antiviral activity against hepatitis B virus (HBV).
A unique series of simple "unnatural" nucleosides has been discovered to inhibit hepatitis B virus (HBV) replication. Through structure-activity analysis it was found that the 3'-OH group of the beta-L-2'-deoxyribose of the beta-L-2'-deoxynucleoside confers specific antihepadnavirus activity. The unsubstituted nucleosides beta-L-2'-deoxycytidine, beta-L-thymidine, and beta-L-2'-deoxyadenosine had the most potent, selective, and specific antiviral activity against HBV replication. Human DNA polymerases (alpha, beta, and gamma) and mitochondrial function were not affected. In the woodchuck model of chronic HBV infection, viral load was reduced by as much as 10(8) genome equivalents/ml of serum and there was no drug-related toxicity. In addition, the decline in woodchuck hepatitis virus surface antigen paralleled the decrease in viral load. These investigational drugs, used alone or in combination, are expected to offer new therapeutic options for patients with chronic HBV infection.
Three simple, related nucleosides, beta-L-2'-deoxycytidine (LdC), beta-Lthymidine (LdT), and beta-L-2'-deoxyadenosine (LdA), have been discovered to be potent, specific and selective inhibitors of the replication hepatitis B virus (HBV), as well as the closely related duck and woodchuck hepatitis viruses (WHV). Structure-activity relationship analysis indicates that the 3'-OH group of the beta-L-2'-deoxyribose of the beta-L-2'-deoxynucleoside confers specific anti-hepadnavirus activity. The simple nucleosides had no effect on the replication of 15 other RNA and DNA viruses, and did not inhibit human DNA polymerases (alpha, beta and gamma) or compromise mitochondrial function. The nucleosides are efficiently converted intracellularly into active triphosphate metabolites that have a long half-life. Once-daily oral administration of these compounds in the woodchuck efficacy model of chronic HBV infection reduced viral load by as much as 10(8) genome equivalents/ml serum and there was no drug-related toxicity. In addition, a decline in WHV surface antigen (WHsAg) paralleled the decrease in viral load. This class of nucleosides displays an excellent overall safety profile. The first compound, LdT, has already entered clinical trials and LdC, currently being developed as a prodrug, is expected to enter the clinic in the near future. These compounds have the potential for use in combination therapy with the goal of achieving superior viral suppression and diminishing the onset of resistance.
To begin an exploration of the structural parameters responsible for the activity of (+)-5'-noraristeromycin toward hepatitis B virus (HBV), three derivatives varied at the C-4' position have been prepared and evaluated. The syntheses began with a Mitsunobu coupling reaction of an appropriate cyclopentanol with 6-chloropurine. The products of these reactions were synthetically altered by standard ammonolysis and deprotection procedures to give the desired products. Evaluation of the new derivatives indicated that removal of the C-4' hydroxyl of (+)-5'-noraristeromycin increased its potency toward HBV by approximately 10-fold.
(+)-5'-Noraristeromycin (1) has shown significant antiviral activity while its 7-deaza analogue 2 is an antitrypanosomal candidate. To determine the relevance of the 4'-hydroxyl hydrogen in these activities, a derivative of 1 (that is, 3) where the C-4' hydroxyl hydrogen has been replaced by a methyl group has been prepared beginning with palladium (0) mediated coupling of the sodium salt of N6-benzoyladenine (9) and (1S,4R)-4-methoxy-2-cyclopenten-1-yl acetate (5). The synthesis of compound 5 is described from (1S,4R)-1-[(tert-butyldimethylsilyl)oxy]-4-hydroxycyclopent-2-ene (6) in three steps. Analogous preparations of the 7-deaza and 8-aza-7-deaza derivatives of 3 related to 2 (that is, 4 and 12) are also reported. The new derivatives (3, 4, and 12) failed to show improved antiviral activity. Compound 12 was the only derivative with some anti-trypanosomal activity, giving 40% inhibition of growth at 100 microM against bloodstream forms of a Typanosoma brucei brucei isolate in a standard in vitro screen. This study indicated that the C-4'-hydroxyl hydrogen plays a role in the medicinal properties of 1 and 2.
A novel strategy for anti-viral intervention of hepatitis B virus (HBV) through the disruption of the proper folding and transport of the hepadnavirus glycoproteins is described. Laboratory reared woodchucks chronically infected with woodchuck hepatitis virus (WHV) were treated with N-nonyl-deoxynojirimycin (N-nonyl-DNJ), an inhibitor of the endoplasmic reticulum (ER) alpha-glucosidases. The woodchucks experienced significant dose dependent decreases in enveloped WHV, resulting in undetectable amounts in some cases. The reduction in viremia correlated with the levels of hyperglucosylated glycan in the serum of treated animals. This correlation supports the mechanism of action associated with the drug and highlights the extreme sensitivity of the virus to this type of glycan inhibitor. At N-nonyl-DNJ concentrations that prevented WHV secretion, the glycosylation of most serum glycoproteins appeared unaffected, suggesting great selectivity for this class of therapeutics. Indeed, this may account for the low toxicity of the compound over the treatment period. We provide the first evidence that glucosidase inhibitors can be used in vivo to alter specific steps in the N-linked glycosylation pathway and that this inhibition has anti-viral effects.
A unique series of simple unnatural L-nucleosides that specifically inhibit hepatitis B virus (HBV) replication has been discovered. These molecules have in common a hydroxyl group in the 3'-position (3'-OH) of the beta-L-2'-deoxyribose sugar that confers antiviral activity specifically against hepadnaviruses. Replacement of the 3'-OH broadens activity to other viruses. Substitution in the base decreases antiviral potency and selectivity. Human DNA polymerases and mitochondrial function are not effected. Plasma viremia is reduced up to 8 logs in a woodchuck model of chronic HBV infection. These investigational drugs, used alone or in combination, are expected to offer new therapeutic options for patients with chronic HBV infection.