Enantioselective total synthesis of batzelladine F and definition of its structure

Batzelladine F (1) was synthesized in enantioselective and stereoselective fashion in 15 steps (longest linear sequence) and 1.7% overall yield from two readily available enantioenriched beta-hydroxy esters, methyl (R)-3-hydroxydecanoate and methyl (R)-3-hydroxybutyrate. Tethered Biginelli condensations are used to assemble both tricyclic guanidine fragments, with the second tethered Biginelli condensation (14 + 16 --> 17) also being employed to join the guanidine fragments. Three diastereomers of batzelladine F, 2-4, were prepared also. A combination of HPLC, optical rotation and CD spectroscopy was employed to distinguish stereoisomers 1-4, proving that 1 is the correct structure of the hexacyclic marine alkaloid batzelladine F.