Discovery and Semisynthesis of Aurantiacin A: A Unique Ascorbylated 9-epi-ent-Kaurane Diterpenoid from the Untapped Plant Isodon aurantiacus

Aurantiacin A (1), a unique ascorbylated meroditerpenoid composed of an unusual 9-epi-spiro-lactone-type ent-kaurane diterpenoid core, ascorbic acid (vitamin C), and syringic acid, and three new 9-epi-spiro-lactone-type ent-kauranoids, aurantiacins B–D (2–4), were isolated from an untapped species, Isodon aurantiacus. Their structures were determined by spectroscopic data analysis, semisynthesis, floating chirality distance geometry calculations, and quantum chemical calculations. Aurantiacin A (1) was found to induce lysosomal biogenesis, and the potential mechanisms underlying this effect were preliminarily explored.