Synthesis and lipid-lowering activities of preussin derivatives

Syntheses of eleven natural and unnatural analogues of preussin, a pyrrolidin-3-ol alkaloid, have been achieved starting from L-phenylalanine. Our work highlighted an efficient strategy to construct the all cis pyrrolidin-3-ols bearing functionalized alkyl side chain via the key Sakurai allylation and cross metathesis reaction which led to the first syntheses of six other preussin analogues including the four natural products, preussins F, G, H and I. The eleven synthetic analogues were evaluated for their inhibitory effects on cholesterol absorption using fluorescent-cholesterol transport assay in human intestinal Caco-2 cells. All analogues at 5 μg/mL statistically reduced cholesterol absorption comparable to 40 μg/mL of a positive drug, ezetimibe, without cytotoxic effect to the Caco-2 cells. Synthetic preussin B exhibited the highest potency of 18.6 % reduction. The synthetic analogues were further evaluated for lipid-lowering effects in human hepatocellular carcinoma HepG2 cells via the expression of five genes related to hepatic lipid metabolism and pro-inflammatory cytokines using real-time PCR. Remarkably, preussin B significantly modulated hepatic lipid metabolism genes by down-regulating HMGR and up-regulating PPARα, rendering preussin B a new and promising candidate for hypolipidemic and hepatic lipid-lowering agent. Nevertheless, the parent compound, preussin, exhibited the most potent antioxidative effect by markedly scavenging intracellular reactive oxygen species in H₂O₂-induced oxidative stress condition in both Caco-2 and HepG2 cell lines.