Steccherins A-D, chamigrane-type sesquiterpenes from the fungus Steccherinum ochraceum with selective inhibition on B lymphocyte proliferation

Four previously undescribed chamigrane sesquiterpenes, namely steccherins A-D, have been isolated from the fungus Steccherinum ochraceum. Their structures were elucidated by extensive spectroscopic analysis, as well as computational methods and single crystal X-ray diffraction. Steccherins A and B possess previously undescribed backbones which might be derived from normal chamigrane sesquiterpenes, especially that steccherin A pos-sesses a spiro[5.6]dodecane carbon skeleton via a ring-rearrangement. Steccherins A, C, and D showed immu-nosuppressive activity with IC50 values ranging from 6.2 to 37.8 mu M. The data suggested that these chamigrane sesquiterpenes have potential selective inhibition on LPS-induced B lymphocyte proliferation.