A new hetisine-type diterpene alkaloid, venudelphine [I], was isolated from the pH 12 fraction of Delphinium venulosum (Ranunculaceae) in addition to previously isolated alkaloids. The structure of venudelphine was established by spectral data. In a previous study (1) with the aerial parts of Delphinium venulosum Boiss. (Ranunculaceae), four hetisine-type alkaloids, hetisine, hetisinone, venulol, and venduson were isolated, the last two compounds being new.In the present investigation, the pH 12 fraction of the same plant extract yielded another new C₂₆ alkaloid, venudelphine [I]. The new compound had a molecular formula C₂₆H₃₃NO₇ (mlz 455.2316, calcd 455.2307). The ir spectrum of 1 showed the presence of acetyl signals at 1737, 1730, and 1240 cm⁻¹. The uv spectrum had only end absorption at 220 nm. The ¹H-nmr spectrum indicated an exomethylene group at δ 4.99 (1H, br s) and 4.82 (1H, br s) (C-17 protons), three acetyl signals at δ 2.09 (3H, s), 2.01 (3H, s), 1.98 (3H, s), and an Me signal at δ 1.05 (3H, s, Me-18); other signals were at δ 2.82 (1H, br d,J= 14 Hz), 2.55 (1H, br d, J= 14 Hz) (C-19 protons), 3.86(1H, s, H-20), and at δ 3.32 (1H, br s, H-6). The signals of hydrogens geminal to acetyl groups were at δ 5.72 (1H, d, J=3.5 Hz, H-1α), 5.31 (1H, dd, J=3.5 and 5 Hz, H-2β), 5.07 (1H, dt,J= 10, 1.5 and 1.5 Hz, H-13β). Spin-decoupling experiments indicated the relationship between H-1 and H-2; when the signals at δ 5.31 (H-2β) and 5.72 (H-1α) were irradiated separately the other signal collapsed to a singlet (H-1) or a doublet (H-2).The stereochemistries at C-1 and C-2 of 1 were decided by measuring the J values and studying Dreiding models. ¹³C-nmr and APT spectra of 1 indicated the presence of four Me quartets, six methylene triplets, nine methine doublets, and seven quaternary carbon atoms and thus suggested a hetisine-type compound with three acetyl groups. As the signals at 71.1, 73.1, and 74.9 ppm were doublets in the ¹³C-nmr spectrum, the acetyl groups could be situated at C-1, C-2, C-3, C-7, C-11, C-15, and C-19; the signals of two doublets at δ 2.82 and 2.55 in the ¹H-nmr spectrum and the signal of a triplet at δ4.10 ppm in the ¹³C-nmr spectrum clearly indicated the C-19 protons. When C-15 bears an acetyl group, the signal for C-16 appears at ca. 150-151 ppm (2). Location of the oxygen functions at C-1, C-3, or C-7 adjacent to quaternary carbon atoms (C-10, C-4, and C-8, respectively) will cause them to be further downfield than expected in the ¹³C-nmr spectrum (3). Although there were no significant shifts in the signals of C-4 and C-8, the signal for C-10 shifted downfield to 52.8 ppm, indicating an acetyl function at C-1 (4).Due to the lack of a signal at ca. 18-20 ppm and the spin-decoupling experiments between H-1 and H-2, the second acetyl group was placed at C-2. The third acetyl group could be situated either at C-11 or C-13. The signals at δ 5.07 (in ¹H nmr) and at 74.9 ppm (in ¹³C nmr) indicated that the acetyl should be at C-13 rather than at C-11. In order to prove this, the related protons beginning from H-20 were irradiated; the signal for H-20 was at δ 3.86 as a singlet, but because the dihedral angle between H-20 and H-14 (δ 2.45, 1H, br d, J= 10 Hz) was 90° they did not couple; nevertheless, irradiation of the signal at δ 3.86 caused a slight sharpening in the signal at δ 2.45, while irradiation of the latter signal (H-14) collapsed the signal at δ 5.07 (1H, dt, H-13) into a triplet (J = 1.5 Hz).Irradiation of the signal at δ 5.07 collapsed the signal at δ 2.45 to a broad singlet, showing the relation between H-13 and H-14, and indicating that the third acetyl group was at C-13. The stereochemistry at this position was decided by selecting the boat shape ring (C-8, C-9, C-11, C-14) as the reference ring and studying the ¹H-nmr spectrum using a Dreiding model. When H-13 has an axial (β) stereochemistry, the dihedral angle between H-13 and H-14 is ca. 35-40°, which was in agreement with the given coupling constant. The spectral data suggested the given formula for 1.