In an attempt to synthesize carvotacetone analogues, new 3-O-benzyl-carvotacetone (10) and previously reported 3-hydroxy-2-isopropyl-5-methyl-p-benzoquinone (11) were synthesized from piperitone (7). In this work, we describe the synthesis of 10 and other analogues from 7. Luche reduction of 7 to cis-piperitol (8), followed by benzylation yielded 3-O-benzyl-piperitol (9). Riley oxidation of 9 afforded corresponding ketone 10, 11 and 3-benzyloxy-4-isopropylcyclohex-1-enecarbaldehyde (12). Structures of these compounds were determined based on NMR, IR and LC-MS spectral data. Compound 11, exhibited antiplasmodial activities against chloroquine-sensitive (D6) and resistant (W2) strains of Plasmodium falciparum with IC50 values of 0.697 and 0.653 µg/mL, respectively. In addition, compound 11 was active against Cryptococcus neoformans with an IC50 value of 3.11 µg/mL, compared to reference standard fluconazole (IC50 value of 1.87 µg/mL), while 10 and 12 were inactive against both organisms. This is the first report of the antiplasmodial and anticryptococcal activity of compound 11.
Keywords: 3-O-benzyl-carvotacetone; 3-hydroxy-2-isopropyl-5-methyl-p-benzoquinone; Cryptococcosis; Piperitone; Riley oxidation; anti-plasmodial.