A series of influenza neuraminidase inhibitors with the cyclohexene scaffold containing lipophilic side chains have been synthesized and evaluated for influenza A and B neuraminidase inhibitory activity. The size and geometry of side chains have been modified systematically in order to investigate structure-activity relationships of this class of compounds. The X-ray crystal structures of several analogues complexed with neuraminidase revealed that the lipophilic side chains bound to the hydrophobic pocket consisted of Glu276, Ala246, Arg224, and Ile222 of the enzyme active site. The structure-activity relationship studies of this series have also demonstrated remarkably different inhibitory potency between influenza A and B neuraminidase. This indicated that the lipophilic side chains had quite different hydrophobic interactions with influenza A and B neuraminidase despite their complete homology in the active site. Influenza B neuraminidase appeared to be much more sensitive toward the increased steric bulkiness of inhibitors compared to influenza A neuraminidase. From the extensive structure-activity relationship investigation reported in this article, GS 4071 emerged as one of the most potent influenza neuraminidase inhibitors against both influenza A and B strains.

Potentially orally bioavailable prodrugs of the antiretroviral agent 9-[2-(phosphonomethoxy)propyl]adenine (PMPA) were evaluated. Alkyl methyl carbamates were synthesized by alkylation of PMPA with the corresponding alkyl chloromethyl carbonate and N-alkyl chloromethyl carbamate reagents. The prodrugs were evaluated for in vitro antiviral activity in addition to chemical and enzymic stability. The inhibition of human immunodeficiency virus type 1 (HIV-1) strain IIIB replication in MT-2 cells by the carbonate prodrugs was found to be 2.S-S00-fold increased compared to PMPA. The alkyl methyl carbonates, except t-butyl methyl carbonate, had reasonable chemical stability at pH 2.2 and 7.4, but were rapidly converted to the corresponding monoester of PMPA in the presence of dog plasma. The alkyl methyl carbamate prodrugs such as N-t-butyl methyl carbamate were found to have high stability in vitro. Based on its chemical stability and good oral bioavailability, bis(POqPMPA (isopropyl methyl carbonate) was chosen as a clinical candidate.

SummaryA series of acyclic phosphonomethylether nucleosides were synthesized and then evaluated for inhibitory activity against respiratory viruses of clinical significance using CPE inhibition, neutral red uptake and virus yield reduction assays. Of the 20 compounds synthesized, none significantly inhibited influenza A or B viruses or respiratory syncytial virus strains A2, Long or 18537; the selective indices (51) were less than 10. A new compound, G5-2128 (2R, 5R-9-[2,5-dihydro-5-(phosphonomethoxy)-2-furanyl]adenine; D4API), selectively inhibited adenovirus 5 (51)10) as did G5-0577 (9-(3-hydroxy-2-phosphonylmethoxypropyl)-adenine; HPMPA) and G5-0504 [(S)-1-[3-hydroxy-2-(phosphonylmethoxypropyl)]-cytosine; HPMPC]. The 50% effective concentrations (EC so) ranged from 8-100 I1g mL-l and 50% cell inhibitory concentrations (CC so )from 40-1000 I1g ml.", All three compounds were also found to be active against laboratory strains and clinical isolates of adenovirus types 1, 2, 8 and 41 with EC so values ranging from 0.2 to 10 I1g ml,". Two compounds, G5-438 (9-(2-phosphonylmethoxyethyl)guanine, PMEG) and G5-2542 (9-[3-phosphonomethoxy)methoxymethyl]guanine) inhibited parainfluenza virus 3 strain C243, with 51 of 52 and >333, respectively. PMEG also inhibited measles virus strains CC, Halonen and Chicago with EC so values ranging from 0.03-9119 ml,". These data suggest that these compounds should be considered for possible development as therapeutic agents for respiratory virus infections.