Reexamination of the structure of veramarine

Abstract

The previously proposed α-orientation for the C(16)-hydroxyl group of the alkaloid veramarine (Ia) has been revised; the 1H and 13C NMR data of Ia and the base-catalyzed solvolysis of its O-diacetate Id evidenced veramarine to be (25S)-cev-5-enine-3β,16β,20β-triol (Ib).

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“…The NOESY correlations between H-16 (δ H 4.46) and H 3 -21 (δ H 1.31) and between H-23β (δ H 1.93) and H 3 -27 (δ H 1.17) indicated the β-axial orientations of HO-16, HO-20, and Me-27 (Figure ). This was confirmed by the 13 C NMR chemical shift values of the associated C-16 (δ C 66.8), C-20 (δ C 73.0), and C-25 (δ C 27.7) stereogenic centers similar to those of veramarine (δ C 66.1, 73.2, and 27.6, respectively) . The splitting pattern and coupling constants of H-17 (dt, J = 12.2, 2.4 Hz) were reminiscent of its anti -relationship with H-13, which established the configuration of C-13 as shown in Figures and .…”

“…This was confirmed by the 13 C NMR chemical shift values of the associated C-16 (δ C 66.8), C-20 (δ C 73.0), and C-25 (δ C 27.7) stereogenic centers similar to those of veramarine (δ C 66.1, 73.2, and 27.6, respectively). 20 The splitting pattern and coupling constants of H-17 (dt, J = 12.2, 2.4 Hz) were reminiscent of its anti-relationship with H-13, which established the configuration of C-13 as shown in Figures 1 and 3. The absolute configuration of 2 was established using the same approach as for 1.…”

“…The 13 C NMR data and a quasimolecular ion at m / z 458.3269 (calcd [M + H] + , m / z 458.3270; Figure S14, Supporting Information) in the HRESIMS led to the assignment of a C 28 H 43 NO 4 molecular formula. The 1D NMR spectra of 2 were found to share significant similarities with those of veramarine, aside from the presence of a formate moiety, as deduced from resonances at δ H 8.06 and δ C 162.5 and the IR absorption at 1715 cm –1 (Tables and ; Figure S15, Supporting Information). The HMBC correlation of the formate proton (δ H 8.06) with C-3 (δ C 75.1) revealed this functionality to be located at C-3 (Figure ).…”