[Structure of chromogen I of the Morgan-Elson reaction].

Alkaline treatment of 2-acetamido-2-deoxy-3,4:5,6-di-O-isopropylidene-aldehydo-D-glucose, or of the analogous D-mannose derivative, gave the same crystalline material, unambiguously identified as 2-acetamido-2,3-dideoxy-alpha-D-erythro-hex-2-enofuranose (3) by n.m.r. and mass spectrometry, and crystallography. Treatment of 3 with methanol in acidic medium gave methyl 2-acetamido-2,3-dideoxy-alpha,beta-D-erythro-hex-2-enofuranoside (11). The identical compound was obtained from Chromogen I under identical conditions.