1,4-dithia-7-azaspiro [4.4]nonane-8(S)-carboxylic acid, methyl ester hydrobromide → Methyl (8S)-1,4-dithia-7-azaspiro[4.4]nonane-8-carboxylate

Participants

Reaction Steps

Dissolve the 1,4-dithia-7-azaspiro[4.4]nonane-8-(S)-carboxylic acid, methyl ester, hydrobromide from paragraph B in 0.1N NaOH and extract with ethyl acetate. Dry the organic layer over magnesium sulfate and concentrate in vacuo to give 1,4-dithia-7-azaspiro [4.4]nonane-8(S)-carboxylic acid, methyl ester (1.35 g). Dissolve the latter in 100 ml of ethyl acetate and treat with 2.07 g of N-benzyloxycarbonyl-(S)-alanine, N-hydroxysuccinimide ester. Stir the reaction mixture at room temperature for eighteen hours and concentrate in vacuo. Place the residue on a column of silica gel (300 g, 60-200 mesh) and elute with hexane:ethyl acetate 4:1 to obtain 7-[N-benzyloxy-carbonyl-(S)-alanyl]-1,4-dithia-7-azaspiro[4.4 ]nonane-8(S)-carboxylic acid, methyl ester, a yellow oil [α]D26 -14.8° (ethanol).

Provenance & Evidence