Structure-activity relationships of the antimalarial agent artemisinin. 1. Synthesis and comparative molecular field analysis of C-9 analogs of artemisinin and 10-deoxoartemisinin

A series of C-9 beta-substituted artemisinin analogs (2-21) were synthesized via dianion alkylation of the total synthetic intermediate 57 followed by subsequent ozonolysis/acidification, or by alkylation of the enolate derived from (+)-9-desmethylartemisinin, 2. Inactive acyclic analogs 22 and 23 were synthesized by nucleophilic epoxide opening and the ring contracted analog 24 was prepared by an alternate route. 10-Deoxo-9-alkyl derivatives 68 and 70 were synthesized convergently from intermediates in the preparation of 9-alkyl derivatives. In vitro bioassay was conducted in W-2 and D-6 clones of drug resistant Plasmodium falciparum. Comparative molecular field analysis (CoMFA) of the 9-alkyl lactone derivatives provided a model with a cross-validated r2 = 0.793. Inclusion of inactive 1-deoxyartemisinin analogs 26-42 provided a model with a value of 0.857. The activities of a number of other analogs of divergent structure (43-56) were predicted with good accuracy using the CoMFA model.