Sterols ofKalanchoe pinnata: First report of the isolation of both C‐24 epimers of 24‐alkyl‐Δ²⁵‐sterols from a higher plant

Eighteen sterols were isolated from the aerial parts of Kalanchoe pinnata (Crassulaceae) including four novel sterols, viz. (24 R )‐stigmasta‐5,25‐dien‐3β‐ol (24‐epiclerosterol), (24 R )‐5α‐stigmasta‐7,25‐dien‐3β‐ol, 5α‐stigmast‐24‐en‐3β‐ol, and 25‐methyl‐5α‐ergost‐24(28)‐en‐3β‐ol. 24‐Epiclerosterol and its Δ 7 ‐analog occur together with their 24 S /β‐epimers in the same plant making this the first report of the isolation of both C‐24 epimers of Δ 25 ‐unsaturated 24‐alkylsterols from a non‐marine organism. Iodine‐catalyzed isomerization of stigmasta‐5,24‐dien‐3β‐ol (24‐ethyldesmosterol), the main sterol of K. pinnata , yielded 24‐epiclerosterol among other products.