A high-performance liquid chromatography (HPLC) method was developed for measuring the concentrations of
clovamide-type phenylpropenoic
acid amides (
N-caffeoyldopamine and
N-caffeoyltyramine) in cell and plasma samples. The separation was performed on a Nova-Pak C18 column using an isocratic
buffer with a coulometric electrochemical detector with four
electrode channels. Using the HPLC method,
N-caffeoyldopamine and
N-caffeoyltyramine could be detected with good peak resolutions at respective retention times (4 and 6.4 min). The calibration curves were linear over the ranges (0.1 and 100 microM), and their lower limit of detection was as little as 100 fmol. For quantifying
N-caffeoyldopamine and
N-caffeoyltyramine in cell and plasma samples, the samples were extracted by extraction methods with more than 95% recoveries. After extraction, the
amides were detected with the same sensitivity, peak resolutions, and retention times. Using this method, plasma concentrations of
N-caffeoyltyramine were determined in blood samples collected at 12, 24, 30, 36, 48, 60, and 75 min after the
oral administrations of
N-caffeoyltyramine (0.5 mg and 2 mg/30 g
body weight). This HPLC method with an electrochemical detector is the first reported method able to quantify
N-caffeoyldopamine and
N-caffeoyltyramine in
biological samples with excellent detection limits, peak resolutions, discrete retention times, and consistent reproducibility.