Identification of the Metabolites of a Novel Anti-MRSA Compound,Kaempferol-3- O -Alpha-L-(2″,3″-di- p -coumaroyl)rhamnoside (KCR),Extracted from American Sycamore

Abstract

Fractionation of an extract from American sycamore leaves produced the small molecule, kaempferol-3-O-alpha-L-(2″,3″-di-p-coumaroyl)rhamnoside (KCR), which exists in four stereoisomeric forms (EE, EZ, ZE, and ZZ) at the olefin in the p-coumaroyl; all four isomers exhibit potent anti-MRSA activity in vitro. As part of the preclinical development of KCR, we set out to investigate the metabolites of KCR in mouse plasma as a prelude of ADME studies and therapeutic assessment. When KCR was added to mouse plasma at 37 °C, two new HPLC peaks appeared with increasing intensity as the incubation time increased; their retention times were shorter than that of KCR indicating that KCR was metabolized to produce two compounds that were more polar. HPLC results indicated that the two metabolites mainly came from the ZE and EE isomers and that the ZZ isomer was the most stable. Based on their respective HPLC retention times and UV spectra, these two metabolites were tentatively identified as p-coumaric acid and afzelin; both of which are more polar than KCR. The molecular weights of both metabolites were then confirmed by a Waters Acquity UPLC system with a QDa mass detector. UPLC chromatograms and molecular ions of metabolites 1 and 2 match well with those of reference materials, p-coumaric acid and afzelin, thus confirming the identities of the two major metabolites of KCR. In summary, KCR was metabolized in mouse plasma and two major metabolites (p-coumaric acid and afzelin) were identified; the metabolites were mainly converted from the ZE and EE isomers.