Krempenes A-D: A series of unprecedented pregnane-type steroids from the marine soft coral Cladiella krempfi

Four new pregnane-type steroids, krempenes A-D (1-4), were isolated from the marine soft coral Cladiella krempfi. Their structures were elucidated on the basis of 1D- and 2D-NMR analyses, as well as MS experiments. Krempene A (1) contains a very unusual structural motif, with a hexacyclic oxadithiino unit fused to the steroidal ring A. Krempene B (2) is a 19-norpregnane steroid, the 19-Me group formally being transferred to position 4. Furthermore, krempene D contains an unusual C=C bond at C(7) of the pregnane skeleton.