The Biosynthesis of Lycopodine

In an effort to investigate the generality of the classical scheme for the generation of pelletierine-type compounds according to Path C1 in Scheme 8,we investigated the incorporation of acetate into lycopodine (27). Based on extensive work with radiotracers performed in the 1960s and 1970s predominantly by Spenser and MacLean, a model had been developed which envisaged the carbon skeleton of lycopodine to arise via the dimerization of pelletierine (28) (Scheme 13 top), which was indeed proven...

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N-oxide - the Two Faces of PAs A unique feature of PAs is that they exist predominantly as their N-oxides. In most plant taxa PAs are exclusively synthesized, distributed and stored as N-oxi-des. In these species the detection of PAs as free base must be regarded as an artifact. PA N-oxides are easily reduced during extraction and sample preparation in the presence of weak reducing agents such as cysteine or other thiols that are abundant in plant materials 23 . There are only a...

D

The mechanisms by which aromatic PKSs control structural diversity are distinct from those for noniterative type I PKSs for reduced polyketide biosynthesis. Aromatic PKSs catalyze the biosynthesis of various polycyclic, mostly aromatic, polyketides (Fig. 2), involving a linear poly- -ketone intermediate such as 5 or 6, and using malonyl coenzyme A (CoA) as an extender unit exclusively (pathway B in Fig. 1). The principal challenges faced by aromatic PKSs are to choose a starter unit, to...

Polyketide Aromatase and Cyclase

Although genetic studies have identified a number of putative polyketide AROs 85 - 89 and CYCs 36,49,84 - 91 , these studies failed to reveal any mechanistic insights for these enzymatic aldol or Claisen condensations. (ARO and CYC are often used interchangeably, and there is little biochemical data to separate them into two subgroups of enzymes.) Biochemical characterizations of these enzymes are difficult because the presumed substrates, whether they are linear or monocyclic poly-b-ketones,...

In Vitro Reconstitution of Type II Polyketide Synthase

Shen and Hutchinson developed the first cell-free system for a bacterial type II PKS in 1993 and succeeded in synthesizing 32 from acetyl and malonyl CoA by the Tcm PKS in vitro 182 . Since then, similar experiments were reported by Khosla and co-workers for the Act PKS 181 . More recently, both the Act PKS 173,184 and the Tcm PKS 183 have been reconstituted in vitro from individually purified components, making it possible to explore many of the mechanistic details of type II PKSs that have...

Introduction

The terpenes are a structurally diverse and widely distributed family of natural products containing well over 30,000 defined compounds identified from all kingdoms of life 1 . The majority of terpenes have been isolated from plants where they serve a broad range of roles in primary metabolism including several plant hormones and the most abundant plant terpenoid, phytol, the side chain of the photosynthetic pigment chlorophyll and in ecological interactions as chemical defenses against...