Determination and properties of acetyl conjugate of N-desisopropylpropranolol, AcNDP.

1-Acetamino-3-(1-naphthyloxy)-2-propanol (AcNDP) detected in human urine was formed as a metabolite of propranolol (PL) via 1-amino-3-(L-naphthyloxy)-2-propanol (N-desisopropylpropranolol, NDP). The excreted amount of AcNDP was determined by GC-MS using an isotope dilution method. More than 40% of total AcNDP in 24 h urine was detected 10 h after the oral administration of PL to two volunteers, and the total amounts during 24 h urine were at least 1.9-3.9% of the PL dose. As AcNDP is an intermediate metabolite of PL, its urinary amount cannot be determined exactly. Incidentally, AcNDP was chemically stable and was not formed from NDP when acetyl CoA was added to the inactivated hepatocyte system. Thus, the acetylation of NDP, an aliphatic primary amine, was confirmed to be catalyzed by N-acetyltransferase, and interestingly, the acetyl conjugation was inhibited not by sulfamethazine but by p-amino benzoic acid.