The stereochemistry of migrated hopanes epimeric at C-21

The structures of four migrated hopanes, isolated from Sorghum bicolor and epimeric at C-21 and/or enantiomeric at the C-8, C-13, C-14, C-17, C-18, and C-21 positions: fernenol, 21-epifernenol (trematol), isoarborinol, and 21-epi-isoarborinol (sorghumol, a previously unidentified pentacycle), have been determined by analysing the chromatographic (g.l.c. and h.p.l.c.), spectral (mass and 1H n.m.r.) and physical constant (m.p.) data of the naturally occurring (free) and chemically synthesized acetate and methyl ether derivatives.