On a course of chemotaxonomical study of Polypodiaceous ferns, we have investigated triterpenoid components of three Microsorium species, M. brachylepis (Baker) Nakaike (collected in Okinawa), M. normale Ching and M. punctatum Copel. (both in Taiwan). More than 50 triterpenoids were detected from the three species along with new triterpenoids described below. Triterpenoid acids: From M. brachylepis and M. normale, fern-7-, fern-8-, fern-9(11)-en-28-oic acid (1-3) and adian-5-en-28-oic acid (4) were isolated as their methyl esters (1a-4a). These compounds are the first example of C-28 oxygenated migrated hopane triterpenoids. Compound 1-4 were not detected from M. punctatum. Cycloartanoids: Cycloartanoid fatty acid ester fraction of M. normale was subjected to HPLC [C_<18>, 5μ, CH_3CN-CHCl_3 (7:3)]. 31-norcyclomargenyl palmitate (5b) and linoleate (5c), and 30,31-bisnorcyclomargenyl palmitate (6b) and linoleate (6c) were isolated. Their structures were established by comparisons of spectral data with related compounds. Free alcohol (5) and its acetate (5a) were also isolated from M. normale and M. punctatum. C_<31>-Triterpenoid hydrocarbons:: C_<31>-Triterpenoid hydrocarbons: 21-methyl-bacchara-12,22(29)-diene (7) and 21-methyldammara-18(28),22(29)-diene (8) were isolated only from the type species of this genus, M. punctatum. The structure of 7 was established by HMBC 2D NMR spectoscopy. The structure of 8 was also established by spectral data. The isolation of C_<31>-triterpenoid hydrocarbon from a natural source is the first example. The occurrence of C_<31> triterpenoid hydrocarbons only in M. punctatum and the absence of 1-4 in M. punctatum is of chemotaxonomic interest.
