First synthesis, characterization, and evidence for the presence of hydroxycinnamic acid sulfate and glucuronide conjugates in human biological fluids as a result of coffee consumption
Hydroxycinnamic acids (HCAs) are among the most abundant dietary polyphenols. Recent bioavailability studies have shown that HCAs enter the blood circulation mainly as glucuronides, which are thus most likely to express their potential health effects. In this work, an efficient synthesis of HCA O-arylglucuronides is developed. As for many xenobiotics, the resilience of HCA O-arylglucuronides in plasma and subsequent delivery to tissues could be governed by their binding to human serum albumin (HSA). Hence, the affinity of HCA O-arylglucuronides for HSA and its possible binding site were investigated by fluorescence spectroscopy. HCA O-arylglucuronides turn out to be moderate HSA ligands (K in the range 1–4 × 104 M−1) that bind HSA in sub-domain IIA, competitively or noncompetitively with other sub-domain IIA ligands such as dansylamide and the flavonol quercetin.
First synthesis, characterization, and evidence for the presence of hydroxycinnamic acid sulfate and glucuronide conjugates in human biological fluids as a result of coffee consumption
A systematic investigation of the human metabolism of hydroxycinnamic acid conjugates was carried out. A set of 24 potential human metabolites of coffee polyphenols has been chemically prepared, and used as analytical standards for unequivocal identifications. These included glucuronide conjugates and sulfate esters of caffeic, ferulic, isoferulic, m-coumaric and p-coumaric acids as well as their dihydro derivatives. A particular focus has been made on caffeic and 3,4-dihydroxyphenylpropionic acid derivatives, especially the sulfate conjugates, for which regioselective preparation was particularly challenging, and have so far never been identified as human metabolites. Ten out of the 24 synthesized conjugates have been identified in human plasma and/or urine after coffee consumption. A number of these conjugates were synthesized, characterized and detected as hydroxycinnamic acid metabolites for the first time. This was the case of dihydroisoferulic acid 3′-O-glucuronide, caffeic acid 3′-sulfate, as well as the sulfate and glucuronide derivatives of 3,4-dihydroxyphenylpropionic acid.