Tosylation/mesylation of 4-hydroxy-3-nitro-2-pyridinones as an activation step in the construction of dihydropyrido[3,4-b] benzo[f][1,4]thiazepin-1-one based anti-HIV agents

Reaction of 4-hydroxy-3-nitropyridinone 8 with TsCl and MsCl, respectively, resulted in rapid and quantitative formation of ditosylate 13 and dimesylate 16. Through chemoselective reaction of 16 with thiophenol 17 the key 4-thioaryl substituted intermediate 18 was obtained in 78% yield. This compound was efficiently converted to the target tricyclic products 4a and b. Compound 4a, in particular, is a potent inhibitor in vitro (IC50 = 2 nM) of wild type HIV-1 replication.