(3S,6S)-3-[2-((S)-4-Hydroxy-6-aza-spiro[2.5]oct-6-yl)-ethyl]-6-methyl-5-oxo-hexahydro-oxazolo[3,2-a]pyrazine-7-carboxylic acid benzyl ester → (3S,6S)-3-[2-((S)-4-hydroxy-6-aza-spiro[2.5]oct-6-yl)-ethyl]-6-methyl-hexahydro-oxazolo[3,2-a]pyrazin-5-one

Participants

Reaction Steps

A solution of (3S,6S)-3-[2-((S)-4-hydroxy-6-aza-spiro[2.5]oct-6-yl)-ethyl]-6-methyl-5-oxo-hexahydro-oxazolo[3,2-a]pyrazine-7-carboxylic acid benzyl ester (200 mg, 0.45 mmol) in EtOH (2 mL) was stirred for 3½ h at room temperature under a hydrogen atmosphere (1 bar) in the presence of palladium (10% on activated charcoal, 96 mg), then insoluble material was removed by filtration through diatomaceous earth. The filtrate was concentrated to afford (3S,6S)-3-[2-((S)-4-hydroxy-6-aza-spiro[2.5]oct-6-yl)-ethyl]-6-methyl-hexahydro-oxazolo[3,2-a]pyrazin-5-one (130 mg). This was redissolved in DCM (2 mL), then 3,4-dichlorophenyl isocyanate (88 mg, 0.45 mmol) was added at 0° C. The ice bath was removed, then after 30 min diethylamine (16 mg, 0.23 mmol) was added and the reaction mixture was evaporated. Chromatography (SiO2; DCM→DCM/MeOH/25% aq. ammonia solution 90:10:0.25) produced (3S,6S,8aS)-3-[2-((S)-4-hydroxy-6-aza-spiro[2.5]oct-6-yl)-ethyl]-6-methyl-5-oxo-hexahydro-oxazolo[3,2-a]pyrazine-7-carboxylic acid (3,4-dichloro-phenyl)-amide [example 1; 17 mg, 8%; white solid, MS 497.3 (M+H)+] and (3S,6S,8aR)-3-[2-((S)-4-hydroxy-6-aza-spiro[2.5]oct-6-yl)-ethyl]-6-methyl-5-oxo-hexahydro-oxazolo[3,2-a]pyrazine-7-carboxylic acid (3,4-dichloro-phenyl)-amide (example 2; 127 mg, 57%; white foam, MS 497.3 (M+H)+].

Provenance & Evidence