Synthesis and antimalarial activity of 3′-trifluoromethylated 1,2,4-trioxolanes and 1,2,4,5-tetraoxane based on deoxycholic acid

Abstract

A series of new steroidal peroxides – 3′-trifluoromethylated 1,2,4-trioxolanes and 1,2,4,5-tetraoxanes based on deoxycholic acid were prepared via the reactions of the Griesbaum coozonolysis and peroxycondensation, respectively. 1,2,4-Trioxolanes were synthesized by the interaction of methyl O-methyl-3-oximino-12α-acetoxy-deoxycholate with CF3C(O)CH3 or CF3C(O)Ph and O3 as the mixtures of four possible stereoisomers at ratios of 1:2:2:1 and in yields of 50% and 38%, respectively. The major diastereomer of methyl 12α-acetoxy-5β-cholan-24-oate-3-spiro-5′-(3′-methyl-3′-trifluoromethyl-1′,2′,4′-trioxolane) was isolated via crystallization of a mixture of stereoisomers from hexane and its (3S,3′R)-configuration was determined using X-ray crystallographic analysis. Peroxycondensation of methyl 3-bishydroperoxy-12α-acetoxy-deoxycholate with CF3C(O)CH3 or acetone led to 1,2,4,5-tetraoxanes in yields of 44% and 37%, respectively. Antimalarial activity of these new steroidal peroxides was evaluated in vitro against the chloroquine-sensitive (CQS) T96 and chloroquine-resistant (CQR) K1 strains of Plasmodium falciparum. Deoxycholic acid 3′-trifluoromethylated 1,2,4,5-tetraoxane demonstrated a good IC50 value against CQR-strain (IC50 (K1) = 7.6 nM) of P. falciparum. Tetraoxane with the acetone subunit demonstrated the best results among all tested peroxides with an IC50 value of 3 nM against the CQ-resistant K1 strain. In general, 1,2,4-trioxolanes of deoxycholic acid are less active than 1,2,4,5-tetraoxanes.