Synthesis and structure analysis of cyclodehydration product of piroxicam: a metabolite detected in dogs and monkeys.

We report here a novel synthesis of 6-methyl-6H-7-oxopyrido[1,2-a]pyrimido[5,4-c]-1,2-benzothiazine-5,5-dioxide or cyclodehydration product of piroxicam, a metabolite detected in dogs and monkeys that was synthesized in 6% yield earlier. The reaction of benzoyl chloride with piroxicam in the presence of triethylamine afforded the piroxicam metabolite in good yield. A comparison of spectral data of the synthesized compound with the reported values remained inconclusive. The structure of the compound was confirmed unambiguously by single-crystal X-ray analysis.