Fungal Carotenoids. II. The Structure of the Carotenoid Acid Neurosporaxanthin.

Abstract

The carotenoid acid neurosporaxanthin has been isolated from Neurospora crassa and N. sitophila. The elucidation of the structure as [beta]-apo-4''-carotenoic acid (C35) (V) was based on the following evidence: Neurosporaxanthin and synthetic V have identical absorption spectra in visible and infrared light, the same partition ratios and cannot be separated chromatographically. Neurosporaxanthin methylester and [beta]-apo-4''-carotenoic (C35) methyl ester (VI) also agreed in the above physical properties and showed the same melting point. Hydride reduction of neurosporaxanthin and VI gave the same mono-ol (VII) as judged by identity in visible light absorption spectra and chromatographic behaviour. By comparison of absorption spectra in visible light, chromatographic properties and partition behavior, it was established that the mono-ols (VII) gave the same aldehyde (IX) on allylic oxidation and the same acetate (VIII) on acetylation. Some anomalous spectral features of neurosporaxanthin and derivatives are discussed. Factors influencing the biosynthetic formation of neurosporaxanthin are briefly reviewed and a plausible pathway of biosynthesis for neurosporaxanthin via [gamma] -carotene (XI) is considered.