Dovyalicin-Type Spermidine Alkaloids from <i>Dovyalis</i> Species

Phytochemical investigations of <i>Dovyalis abyssinica</i>, <i>D. hebecarpa</i>, and <i>D. macrocalyx</i> revealed two new spermidine-type alkaloids, dovyalicin E (<b>3</b>) and dovyalicin F (<b>4</b>), along with the previously described dovyalicin A (<b>1</b>), dovyalicin B (<b>2</b>), and dovyalicin C (<b>5</b>). In addition, a new phenol glucoside, 4-hydroxytremulacin (<b>7</b>), and the new 1,2-cyclohexanediol glucoside <b>9</b>, as well as the known compounds methyl 1-hydroxy-6-oxocyclohex-2-enecarboxylate (<b>6</b>) and tremulacin (<b>8</b>), were isolated. The structures were established using homo- and heteronuclear two-dimensional NMR experiments and chiroptical methods. At ambient temperature, the <i>N</i>-disubstituted amide <b>4</b> exists as a mixture of <i>cis</i> and <i>trans</i> conformers. Variable-temperature <sup>1</sup>H 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 Δ<i>H</i><sup>⧧</sup> = 89 ± 4.6 kJ/mol, Δ<i>S</i><sup>⧧</sup> = 65 ± 14 kJ/mol·K, and Δ<i>G</i><sup>⧧</sup>(298K) = 70 ± 4.5 kJ/mol.