Question

Coibacin B is a natural product that exhibits potent anti-inflammatory activity and potential activity in the treatment of leishmaniosis, a disease caused by certain parasites (Org. Let. 2012, 14, 3878-3881) Assign the configuration of each chirality center in coibacin B. Identify the number of possible stereoisomers for this compound, assuming that the geometry of the alkenes are fixed.

Answer 1

(a) Assign the configuration of each chirality center in coibacin B. (b) Identify the number of possible stereoisomers for this compound, assuming that the geometry of the alkenes are fixed. There are total 3 stereocenters present in this molecule. Total 23- 8 isomers possible

According to the chan-Ingold prelog rules priorities given to the chiral carbon. Greater priority will

get number 1 and lower will get 4, If molecule rotating from 1to 3 via colck wise will get R configuration.

If rotating counter clockwise direction get S configuration. In the both cases, lower priority group should be

back side. If not, the configuration exactly reversed. R will get S and S will get R configurations.

Answer 2

Chan-Ingold Prelog rule for determining configuration of chiral Centre Priorities of atoms and groups decided by their atomic mass. In 3D geometry form fourth priority group always must below the plane, and first priority group must be above the plane or in the plane for original configuration If, the fourth priority group is above the plane, then configuration can be inverted In Fischer projection form If the fourth priority group is in the horizontal line, then the configuration can be inverted, But, if the fourth priority group at the vertical line, then configuration can be original. Configuration at chiral centers, are as follows:

On fixing the geometry of alkene that is E for both the possible stereoisomers are, a:s Tollows: Me Me Me Me Me Me Hence, there are eight possible stereoisomers formed