A new phenanthrene and a new 9,10-dihydrophenanthren from Bulbophyllum retusiusculum

A new phenanthrene, bobulretin A (1), and a new 9,10-dihydrophenanthrene, bobulretin B (2) along with four known bibenzyls (3–6) were isolated from the whole plants of Bulbophyllum retusiusculum. Their structures were elucidated by means of extensive spectroscopic analysis. Bobulretin B (2), isolated as enantiomer mixture with unequal proportions, was verified by analysis on a chiral OD-H HPLC column. Compounds 1, 3 and 4 were evaluated for their α-glucosidase inhibitory activity. Neither of them showed obvious activity.