A new depigmenting-antifungal methylated grindelane from Grindelia chiloensis

Abstract

The new methylated grindelane diterpenoid, 7β‐hydroxy‐8(17)‐dehydrogrindelic acid (1b), together with the known 7α‐hydroxy‐8(17)‐dehydrogrindelic acid (2a), 6‐oxogrindelic acid (3a), 4β‐hydroxy‐6‐oxo‐19‐norgrindelic (4a), 19‐hydroxygrindelic acid (5a), 18‐hydroxygrindelic acid (6a), 4α‐carboxygrindelic acid (7a), 17‐hydroxygrindelic acid (8a), 6α‐hydroxygrindelic acid (9a), 8,17‐bisnor‐8‐oxagrindelic acid (10a), 7α,8α‐epoxygrindelic acid (11a), and strictanonic acid (12a) as methyl esters were obtained from an Argentine collection of Grindelia chiloensis (Cornel.) Cabrera. Their structures and relative configurations were established on the basis of spectroscopic analysis. CHCl3 extract from the aerial parts and their pure compounds were evaluated for their antifungal and depigmenting effects. Methyl ester derivative of 10a (10b) exhibited a remarkable mycelial growth inhibition against Botritis cinerea with an IC50 of 13.5 μg ml−1. While the new grindelane 1b exerted a clear color reduction of the yellow‐orange pigment developed by Fusarium oxysporum against UV‐induced damage.