Phenanthrenes from Eulophia macrobulbon as Novel Phosphodiesterase-5 Inhibitors

Phosphodiesterase 5 (PDE5) inhibitors can be used for the treatment of erectile dysfunction and pulmonary hypertension. In order to search for new leads of PDE5 inhibitors, we investigated the chemical constituents of the tubers of Eulophia macrobulbon (E.C. Parish & Rchb. f) Hook. f A new phenanthrene, 9,10-dihydro-4-(4′-hydroxybenzyl)-2,5-dimethoxyphenanthrene-1,7-diol (1) and three known phenanthrenes i.e.,...