Dovyalicin-Type Spermidine Alkaloids from Dovyalis Species

Abstract

Phytochemical investigations of Dovyalis abyssinica, D. hebecarpa, and D. macrocalyx revealed two new spermidine-type alkaloids, dovyalicin E (3) and dovyalicin F (4), along with the previously described dovyalicin A (1), dovyalicin B (2), and dovyalicin C (5). In addition, a new phenol glucoside, 4-hydroxytremulacin (7), and the new 1,2-cyclohexanediol glucoside 9, as well as the known compounds methyl 1-hydroxy-6-oxocyclohex-2-enecarboxylate (6) and tremulacin (8), were isolated. The structures were established using homo- and heteronuclear two-dimensional NMR experiments and chiroptical methods. At ambient temperature, the N-disubstituted amide 4 exists as a mixture of cis and trans conformers. Variable-temperature 1H NMR studies showed that time-averaged spectra are obtainable at 348 K, and the activation parameters determined for the rotation about the amide bond were ΔH⧧ = 89 ± 4.6 kJ/mol, ΔS⧧ = 65 ± 14 kJ/mol·K, and ΔG⧧(298K) = 70 ± 4.5 kJ/mol.