Structure–activity relationships of flavonoids for vascular relaxation in porcine coronary artery

Several types of flavonoids were tested for their ability to relax coronary arteries that were isolated from pig. In addition, vasodilatory activities of these flavonoids were characterized according to their respective chemical structure. The findings provide information on the chemical parameters that are predictive of the relaxation activities of flavonoids. Flavonoids are polyphenolic compounds that are widespread in the plant kingdom, and structure–activity relationships (SAR) for vascular relaxation effects were examined for 17 of them using porcine coronary arteries. Density functional theory was employed to calculate the chemical parameters of these compounds. The order of potency for vascular relaxation was as follows: flavones (apigenin and luteolin) ⩾ flavonols (kaempferol and quercetin) > isoflavones (genistein and daidzein) > flavanon(ol)es (naringenin) > chalcones (phloretin) > anthocyanidins (pelargonidin) > flavan(ol)es ((+)-catechin and (−)-epicatechin). SAR analysis revealed that for good relaxation activity, the 5-OH, 7-OH, 4′-OH, C2 C3 and C4 O functionalities were essential. Comparison of rutin with quercetin, genistin with genistein, and puerarin with daidzein demonstrated that the presence of a glycosylation group greatly reduced relaxation effect. Total energy and molecular volume were also predictive of their relaxation activities. Our findings indicated that the most effective relaxing agents are apigenin, luteolin, kaempferol and genistein. These flavonoids possess the key chemical structures demonstrated in our SAR analysis.