Total Synthesis of (-)-Tatarinoid B

Background: (-)-Tatarinoids A, B, and C are 3 of 19 compounds that have been isolated from the rhizome of the plant Acorus tatarinowii. Used in Chinese medicine, Acorus tatarinowii possesses pharmacological effects on the central nervous system by regulating cyclic adenosine monophosphate (cAMP) activity. Previously published computational studies suggested R configurations for all three natural products. No synthesis of (-)- Tatarinoids A and B had been reported, while (-)- Tatarinoid C had been previously investigated and we have reported on the first total synthesis of its enantiomer. Objective: Herein, we describe the syntheses of (-)-Tatarinoids A, B, and C in 1 to 5 steps. Herein we also report on how our synthetic studies of (-)-Tatarinoids A, B, and C allowed for structure elucidation and we revised the stereochemical configurations of all three natural products. Method: (-)-Tatarinoid A and (-)-Tatarinoid C are both constructed in 3 steps from 1-bromo-2,4,5- trimethoxybenzene. Results: We have completed the syntheses of these natural products in overall yields of 63% and 74%, respectively and in greater than 99% ee. (-)-Tatarinoid B is also synthesized from 1-bromo-2,4,5-trimethoxybenzene in five steps with an overall yield of 11% and in greater than 99% ee. Conclusion: We have concluded the correct stereochemical assignment for all three Tatarinoids is an S configuration rather than the originally proposed R stereochemistry.