Biocatalyzed synthesis and structural characterization of monoglucuronides of hydroxytyrosol, tyrosol, homovanillic alcohol, and 3-(4′-hydroxyphenyl)propanol

The biocatalytic synthesis and purification Of O-beta-D-monoglucuronide conjugates of hydroxytyrosol, tyrosol, homovanillic alcohol, and 3-(4'-hydroxyphenyl)propanol, using porcine liver microsomes, are described here. The glucuronides were synthesized, analyzed and separated by HPLC-UV, identified by HPLC-MS, and their structures unequivocally established by NMR techniques. The outcome of the glucuronidation reaction depends on the structure of the phenolic compounds. Thus, the glucuronidation of hydroxytyrosol, biocatalyzed with porcine liver microsomes, proceeded exclusively on the phenolic hydroxy groups. The regioselectivity was similar to that observed for human and rat liver microsomes, the 4'-hydroxy position being more favorable than the 3'-hydroxy one. In the case of tyrosol, homovanillic alcohol, and hydroxyphenylpropanol, two products were formed during microsomal glucuronidation: a major one, the phenolic O-beta-D-glucuronidated derivative and, a minor one, the O-beta-D-glucuronidated aliphatic alcohol.