The above evidence definitely establishes the structure of the Ca-substituent as a p- aldehydoester. Its position is fixed at C16 by the nature of the various alstyrines produced, and these also establish the remaining skeletal structure of geissoschizine. Confirmation of the indolic NH and enolic 0-H was provided by infrared bands at 2.90 and 3.30 p, respectively, which were shifted to 3.88 and 4.00 after exchange in deuterium methoxide. ...
