The acyl glucuronide of 2-(4-diethylamino-2-hydroxybenzoyl)benzoic acid: Synthesis, structural assignment, occurrence as a human phase II metabolite of Uvinul® A Plus and acute aquatic toxicity

Abstract

This work was undertaken to address the potential environmental impact of the UVA filter Uvinul® A Plus (DHHB) upon its biotransformation in humans. For this purpose, the putative human metabolite 3 was prepared by a three-step synthetic sequence involving the initial Koenigs-Knorr reaction of 2-(4-diethylamino-2-hydroxybenzoyl)benzoic acid (DHB) with acetobromo-α-d-glucuronic acid methyl ester, which afforded the corresponding peracetylated DHB-acyl glucuronide (1). Subsequent enzymatic deprotection with amano lipase A (LAS) led to the 2-(4-diethylamino-2-hydroxybenzoyl)benzoyl-β-D-glucuronide methyl ester (2). Final deprotection of compound 2 was achieved with porcine liver esterase (PLE), giving the target 2-(4-diethylamino-2-hydroxybenzoyl)benzoyl-β-D-glucuronide (3). The synthesized DHB-acyl glucuronide 3 was identical to the key phase II metabolite of DHHB in human hepatocytes. Acute toxicity of 2 and 3 was evaluated by means of the Aliivibrio fischeri bioluminescence inhibition assay, obtaining EC₅₀ values of 22.1 mg L^-1 and 105.1 mg L^-1, respectively. According to the toxicity categories established by international consensus and considering that feasible concentrations of solar filters in aquatic ecosystems are several orders of magnitude lower, the glucuronide derivative of DHHB could in principle be considered as non-hazardous to the aquatic environment.