Anti-HSV-1 and HSV-2 Flavonoids and a New Kaempferol Triglycoside from the Medicinal Plant Kalanchoe daigremontiana.

Kalanchoe daigremontiana (Crassulaceae) is a medicinal plant native to Madagascar. The aim of this study was to investigate the flavonoid content of an aqueous leaf extract from K. daigremontiana (Kd), and assess its antiherpetic potential. The major flavonoid, kaempferol 3-O-β-d-xylopyranosyl-(1 → 2)-α-l-rhamnopyranoside (1), was isolated from the AcOEt fraction (Kd-AC). The BuOH-soluble fraction afforded quercetin 3-O-β-d-xylopyranosyl-(1 → 2)-α-l-rhamnopyranoside (2) and the new kaempferol 3-O-β-d-xylopyranosyl-(1 → 2)-α-l-rhamnopyranoside-7-O-β-d-glucopyranoside (3), named daigremontrioside. The crude extract, Kd-AC fraction, flavonoids 1 and 2 were evaluated using acyclovir-sensitive strains of HSV-1 and HSV-2. Kd-AC was highly active against HSV-1 (EC50  = 0.97 μg/ml, SI > 206.1) and HSV-2 (EC50  = 0.72 μg/ml, SI > 277.7). Flavonoids 1 and 2 showed anti-HSV-1 (EC50  = 7.4 μg/ml; SI > 27 and EC50  = 5.8 μg/ml; SI > 8.6, respectively) and anti-HSV-2 (EC50  = 9.0 μg/ml; SI > 22.2 and EC50  = 36.2 μg/ml; SI > 5.5, respectively) activities, suggesting the contribution of additional substances to the antiviral activity.