New iridoid glycosides from Anarrhinum pubescens

Six metabolites (1-6) were isolated from the aerial parts of Anarrhinum pubescens Fresen. (Plantaginaceae) growing in Saint Catherine region in Egypt; two of them (1 and 4) are here reported to be newly identified naturally occurring iridoids. The isolated metabolites were identified as 6-O-foliamenthoyl-(6'-O-cinnamoyl)-antirrhinoside (1), 6'-O-cinnamoyl-antirrhinoside (2), the iridoid dimer, pubescensoside (4), antirrhinoside (5), 10-hydroxy-antirrhinoside (6), and the flavonoid, diosmin (3). Identification of the new metabolites was based on analysis of their collected spectroscopic data (NMR and HR-ESI-MS). Furthermore, compounds (1, 4, and 5) were subjected to cytotoxic testing against the human lung carcinoma cell line (A-549); compound 4 showed better cytotoxic activity as indicated by the obtained (IC₅₀).