[CH3:1][O:2][C:3](=[O:21])[CH2:4][C:5]1([CH2:19][CH3:20])[C:10]2[NH:11][C:12]3[C:17]([C:9]=2[CH:8](N)[CH2:7][O:6]1)=[CH:16][CH:15]=[CH:14][CH:13]=3.[OH2:22].C=O>C1COCC1>[CH3:1][O:2][C:3](=[O:21])[CH2:4][C:5]1([CH2:19][CH3:20])[C:10]2[NH:11][C:12]3[C:17]([C:9]=2[CH:8]([OH:22])[CH2:7][O:6]1)=[CH:16][CH:15]=[CH:14][CH:13]=3To a solution of 4-amino-1-ethyl-1,3,4,9-tetrahydropyrano[3,4-b]indole-1-acetic acid methyl ester (6 g, 0.020 mol) in 50 mL THF was added 50 mL of H2O and paraformaldehyde (5 g) and the solution was heated at reflux for 2 hours under nitrogen. It was then cooled, concentrated in vacuo, and diluted with ethyl acetate. The ethyl acetate layer was washed with saturated sodium bicarbonate solution, brine, dried and concentrated in vacuo. The residue was purified by flash chromatography eluting with hexane to give a white solid (4 g, 66.4% ) m.p. 86°-90° C.
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