Bioactive Dimeric Acylphloroglucinols from the Mexican Fern Elaphoglossum paleaceum

Two new prenylated acylphloroglucinols, paleacenins A (1) and B (2), were isolated from the rhizome n-hexane and chloroform extracts of the fern Elaphoglossum paleaceum. Both compounds were found to possess the same geranylated filicinic acid moiety but have a different phloroglucinol ring substituent. Their structures were determined using ¹H and ¹³C NMR spectroscopic, HRMS, and ECD analysis. The plant extracts and purified compounds were assayed for inhibition of Monoamine Oxidase (MAO) activity, and the n-hexane and chloroform extracts displayed 25.0% and 26.5% inhibition of MAO-A, respectively, as well as 42.5% and 23.7% inhibition of MAO-B, respectively. Compounds 1 and 2 exhibited IC₅₀ values of 31.0 (1.3) μM for MAO-A and 4.7 (4.4) μM for MAO-B. Paleacenin A (1) showed a higher selective index (SI) toward MAO-B (SI_MAO-B/MAO-A 0.1), and paleacenin B (2) exhibited selectivity to MAO-A (SI_MAO-B/MAO-A, 3.5). The extracts showed cytotoxicity against a panel of prostate, cervix, breast, and colon Cancer cell lines (IC₅₀ values between 1.7 and 10.6 μg/mL); the pure compounds were more active against the prostate, cervix, and colon Cancer cell lines. Paleacenins A (1) and B (2), with IC₅₀ values of 46 and 41 μM, respectively, inhibited nitric oxide production by the RAW264.7 murine macrophage model.