The Absolute Configurations of Haliclonacyclamines A and B Determined by X-Ray Crystallographic Analysis

X-Ray crystallography establishes that the marine alkaloids (–)-haliclonacyclamine A 1 and (+)-haliclonacyclamine B 2 each have the configuration C2 (R), C3 (R), C7 (R), and C9 (R). The alkaloids appear to be enantiomerically pure; this provides an insight into the stereochemical consequences of the biosynthetic pathway leading to these bioactive 3-alkylpiperidine alkaloids.