10.1021/bi00840a054
The research investigates the biosynthesis of gentiopicroside and loganic acid, two monoterpene glucosides found in the plant Swertia caroliniensis. The study aims to elucidate their biosynthetic pathways and confirm their mevalonoid origin. Key chemicals used include acetate-2-14C, mevalonate-2-14C, and mevalonate-2-3H-2-14C as labeled precursors. Through tracer experiments and various chemical transformations such as methylation, acetylation, and oxidation, the researchers demonstrated that both compounds originate from mevalonate. They also revised the structure of gentiopicroside based on chemical and spectral data, including double-resonance nuclear magnetic resonance studies. The results support a biogenetic scheme where mevalonate is converted to geranyl pyrophosphate, then to loganic acid, which undergoes ring cleavage to form gentiopicroside. The study concludes that loganic acid and its derivatives play a significant role as precursors for various iridoids and secoiridoids, and potentially for indole alkaloids, highlighting the interconnected biosynthetic pathways of these plant metabolites.