Unusual Type of a “Head-to-Head, Tail-to-Tail” Homochiral Cyclic Dimer in the 15-Ene-Steviol Crystal Hydrate

A new crystal form (Z′ = 3) of 15-ene-steviol, 13-hydroxy-ent-kaur-15-ene-19-oic acid, is prepared. A homochiral “head-to-head, tail-to-tail” cyclic dimer (previously unknown associate for compounds with a kaurane skeleton) is determined by XRD. The conducted quantum chemical calculations indicate that the dimer has a strained geometry, both in crystal and gas phases, which is manifested as a significant deviation from the carboxyl synthon plane. The topological analysis and the electron density Laplacian analysis show that the lone pairs of carbonyl groups deviate from bond paths.