Abstract
The biosynthesis of verrucosan-2beta-ol in the green phototrophic eubacterium Chloroflexus aurantiacus was investigated by in vivo incorporation of singly or doubly 13C-labeled acetate. The 13C labeling of the isolated diterpene was analyzed by one- and two-dimensional NMR spectroscopy. The 13C-labeling patterns of verrucosan-2beta-ol were compared with the labeling patterns of intermediary metabolites (acetyl-CoA, pyruvate, and glyceraldehyde 3-phosphate) which were deduced from amino acids and nucleosides by retrobiosynthetic analysis. The results show that verrucosan-2beta-ol is synthesized via mevalonate and not via the deoxyxylulose pathway, which was discovered recently in some eubacteria, algae, and plants. A scheme for the formation of the unusual tetracyclic ring system is offered. The cyclization process is initiated by the solvolysis of pyrophosphate from geranyllinaloyl pyrophosphate and the mechanism involves a Wagner-Meerwein rearrangement, a 1,5-hydride shift, and a cyclopropylcarbinyl to cyclopropylcarbinyl rearrangement.
Highlights
The biosynthesis of verrucosan-2-ol in the green phototrophic eubacterium Chloroflexus aurantiacus was investigated by in vivo incorporation of singly or doubly 13C-labeled acetate
The 13C-labeling patterns of verrucosan-2-ol were compared with the labeling patterns of intermediary metabolites which were deduced from amino acids and nucleosides by retrobiosynthetic analysis
The labeling pattern of cellular amino acids and nucleosides served as a basis for the reconstruction of central metabolic pools by retrobiosynthetic analysis [5]. These data clearly show that isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP) are formed by the mevalonate pathway in C. aurantiacus
Summary
(Received for publication, December 31, 1997, and in revised form, April 30, 1998). Christoph Rieder‡, Gerhard Strauߧ, Georg Fuchs§, Duilio Arigoni¶, Adelbert Bacher‡, and Wolfgang Eisenreich‡ʈ. The diterpene verrucosan-2-ol (compound 1, Fig. 1) has been isolated recently by Hefter et al [11] from the membrane fraction of C. aurantiacus in yields of 1–2 mg from a 1-g cell mass (dry weight) This rare diterpene with an unusual 3,6,6,5-tetracyclic ring system had been described only in marine sponges [12] and some liverworts (hepaticae) [13,14,15,16,17,18,19,20,21], which are considered as early members of the evolution of terrestrial plants. The labeling pattern of cellular amino acids and nucleosides served as a basis for the reconstruction of central metabolic pools by retrobiosynthetic analysis [5] These data clearly show that IPP and DMAPP are formed by the mevalonate pathway in C. aurantiacus. A specific cyclization mechanism for the formation of verrucosan type diterpenes is proposed
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