Absolute configuration of C-16 of eburnane alkaloids from Kopsia larutensis

The Synthesis of Melohenine B and a Related Natural Product

“…In order to determine the absolute configuration of natural 1a , a highly enantioenriched sample was prepared from (−)- 7 . As the absolute stereochemistry of (−)- 7 is known to be 3 S , 16 S , our sample of optically enriched 1a has the absolute configuration aR ,3 S ,14 R ,16 S . Comparison of the optical rotation of our synthetic 1a with the literature value , showed that synthetic 1a was in the opposite enantiomeric series, and therefore the absolute configuration of naturally occurring 1a can now be assigned as aS ,3 R ,14 S ,16 R…”

Synthesis of 15-methylene-eburnamonine from (+)-vincamine, evaluation of anticancer activity, and investigation of mechanism of action by quantitative NMR

“…Even though the conversion of eburnamonine 2 into 15-methylene-eburnamonine 4 was accomplished in two steps, the yield was quite low (i.e., 28%). The steric congestion at the C16 position of 2 is apparent in its X-ray structure 20 and prevents the installation of the α-methylene group using many other standard protocols; therefore the trifluoroacetate-release olefination approach was required to access the target 4 . In order to conduct a more extensive biological evaluation of 4 in malignant cells as well as define its mechanism of action, an improved synthesis was clearly needed.…”