Deprea bitteriana, (Werderm.) N. W. Sawyer & Benitez (Werderm.) N. W. Sawyer & Benitez

Casero, Carina N., Oberti, Juan C., Orozco, Clara I., Cárdenas, Alejandro, Brito, Iván, Barboza, Gloria E. & Nicotra, Viviana E., 2015, Withanolides from three species of the genus Deprea (Solanaceae). Chemotaxonomical considerations, Phytochemistry 110, pp. 83-90 : 84

2.1. Withanolides isolated from D. bitteriana

D. bitteriana afforded the new compounds withaphysalins V (1) and W (2). Withaphysalins are characterized by oxygenation at the Me(18) group to the level of an alcohol, aldehyde, or acid functioality, which in the latter two cases can lead to cyclization with OH-C(20) to yield a hemiacetal or a lactone. The hemiacetal arrangement is characterized by the absence of the methyl-18 1 H NMR singlet at low-frequency shift, and by the appearance of two methine carbynolic resonances, indicating the presence of R / S mixtures of epimeric hemiacetals at C-18.

The HRESIMS of withaphysalin V (1) showed a molecular ion [M+Na] + at m / z 491.2383, corresponding to an elemental formula of C 28 H 36 O 6 Na. Inspection of the 1D and 2D NMR spectroscopic data indicated that compound 1 possessed rings C and D, as well as the side-chain closely related to those of withaphysalins B [isolated for the first time from Physalis minima ( Glotter et al., 1975) ], F, and G [isolated for the first time from Eriolarynx lorentzii ( Misico et al., 2000) ]. The absence of a signal for CH 3 -18 and the presence of two proton resonances at δ 5.18 (1H, br s) (50%) and 5.31 (1H, br s) (50%) ( Table 1 ) were indicative of a lactol functionality at C-18 and were assigned to the 18 R and 18 S epimers, respectively. The 13 C NMR spectrum showed methine signals at δ 101.3 and 103.9 ppm (C-18 R / S) and resonances at δ 58.1/58.9, δ 56.8/56.8, and δ 84.9/85.2 assigned at C-13 R / S, C-17 R / S, and C-20 R / S, respectively, thus confirming a five-membered lactol ring ( Table 3 ). The doublet of doublets at δ 4.46/4.54 (H-22 R / S), together with the two three-proton singlets at δ 1.88 (H 3 -27) and 1.95 (H 3 -28), indicated the presence of a δ lactone as a side-chain. The resonances at δ 80.6/80.4 (C-22 R / S), 148.0/148.8 (C-24 R and S), 121.9/122.2 (C-25 R and S), 165.6/165.7 (C-26 R and S), 12.4/12.5 (C-27 R and S), and 20.4/20.5 (C-28 R and S), observed in the 13 C NMR spectrum, were in agreement with a δ lactone. Regarding rings A and B, the 1 H NMR spectrum of the epimeric mixture showed characteristic signals of H-2, H-3, and H-6 hydrogens for a 1-oxo-2,5-withadienolide at δ 5.91 (dd, H-2), 6.81/6.80 (ddd, H-3), and 5.84/5.83 (m, H-6), respectively ( Ramacciotti and Nicotra, 2007). The correlation found between H-6 with H-7 at δ 3.95 in the COSY spectrum suggested the hydroxy group to be at C-7. Olefinic resonances at δ 128.0, 144.9/144.6, 141.4/140.9, and 126.0/126.4, a carbonyl carbon at δ 203.0/203.3 (C-1 R / S), and a carbynolic carbon at δ 64.5 (C-7 R / S) were observed in the 13 C NMR spectrum. The OE orientation of the hydroxy group at C-7 was established by a NOESY experiment. The NOE observed between H-7 and H-8 R / S (δ 1.51/1.92) indicated the b orientation of H-7. Accordingly, the structure of compound 1 was determined as shown.

The molecular formula of withaphysalin W (2) was determined by HRESIMS as C 28 H 36 O 6 . Similar to 1, compound 2 was demonstrated to be a 1:1 epimeric mixture from its 1 H NMR spectrum, which showed characteristic H-18 epimeric protons resonating at δ 5.21 s and 5.31 s. Their 1 H and 13 C NMR spectra were closely related to those of compound 1, differing only in the substitution pattern of ring A ( Tables 1 and 3 ). A 1 -oxo-3,5-diene-7 a -hydroxy substitution pattern was inferred from the following observations: (i) two mutually coupled olefinic signals resonating at δ 5.81 (m) and 6.10 (br d, J = 9.7 Hz) assigned to H-3 and H-4, respectively; (ii) the downfield shift of the carbonyl carbon in the 13 C NMR spectrum from δ 203.0/203.3 for compound 1 to δ 209.6/209.8 for compound 2, assigned to C-1; (iii) the downfield shift of H 3 - 19 in the 1 H NMR spectrum from δ 1.21/1.23 for 1 to δ 1.32/1.34 for 2. The 13 C NMR signals corresponding to the A and B rings of withaphysalin W were in agreement with the proposed structure ( García et al., 2012).