New Cleistanthane Diterpenoids from Vellozia pyrantha A.A.Conc and Their Cytotoxic Activity

Four new cytotoxic cleistanthane diterpenoids, named pyranthanols A-B (1-2) and pyranthanones A (3-4), were isolated from Vellozia pyrantha A.A.Conc resin, along with four known compounds (5-8). These compounds show varying degrees of oxidation with hydroxyl and carbonyl groups at different positions of the cleistanthane core skeleton. Their structures were proposed after careful analysis of ¹H and ¹³C NMR, HMBC, HMQC, and COSY and NOESY 1D data and comparison with the literature. Pyranthanol B (2) and pyranthanones A-B (3-4) were active against a lung carcinoma cell line (H-1299) with IC₅₀ values varying from 27.57 ± 6.89 to 99.96 ± 22.64 μM, whereas pyranthanol B (2) and pyranthanone B (4) were active against a human liver carcinoma cell line (HepG2) with IC₅₀ values of 36.21 ± 11.97 and 43.63 ± 25.53 μM, respectively. Pyranthanol B (2) and pyranthanone A (3) were also toxic against a normal lung cell line (MRC-5) with IC₅₀ values of 49.99 ± 19.98 and 43.63 ± 43.63 ± 20.25 μM, respectively. The moderate activity observed may suggest these compounds as potential candidates for drug development against carcinoma cell lines.