3-(8-ethynyl-5-methyl-6-oxo-4h-imidazo[1,5-a][1,4]benzodiazepine-3-carbonyl)oxypropyl 8-ethynyl-5-methyl-6-oxo-4h-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylate