Spirochensilides A and B, Two New Rearranged Triterpenoids from Abies chensiensis

Two new triterpenoids, spirochensilides A (1) and B (2) were isolated from Abies chensiensis. Comprehensive spectroscopic analysis revealed that 1 and 2 are the first example of triterpenoids possessing a unique 8,10-cyclo-9,10-seco and methyl-rearranged carbon skeleton. The single crystal X-ray diffraction analyses and computational methods allowed the absolute configuration assignments of the two compounds. A plausible biogenetic pathway of spirochensilide A (1) is also proposed.