Natural products biochemical studies

Supercritical fluid extraction is a new separation technique that finds a number of applications in the natural products, biochemicals, food, pharmaceuticals, petroleum, fuel, and polymer industries (1-8). There is now an interest in applying this technology in the pulp and paper industry (9,10). In a recent comprehensive study on the interaction of supercritical fluids with lignocellulosic materials, it has been shown that lignin can be not only extracted from wood by reactive supercritical fluids but also separated as solid products in solvent-free form by reducing the extraction fluid pressure from a supercritical to sub critical level (11,12). 

Applications of NMR of interest in biochemistry can be grouped into three major categories (I) determination of the structure of biologically active compounds -especially new natural products (2) studies of biochemical reactions, or processes, especially in vivo and (3) studies of macromolecular structure and dynamics. In the... 

The study of biochemical natural products has also been aided through the application of two-dimensional GC. In many studies, it has been observed that volatile organic compounds from plants (for example, in fruits) show species-specific distributions in chiral abundances. Observations have shown that related species produce similar compounds, but at differing ratios, and the study of such distributions yields information on speciation and plant genetics. In particular, the determination of hydroxyl fatty acid adducts produced from bacterial processes has been a successful application. In the reported applications, enantiomeric determination of polyhydroxyl alkanoic acids extracted from intracellular regions has been enabled (45). 

Saponins are glycosylated secondary metabolites that are widely distributed in the Plant Kingdom.3,4 They are a diverse and chemically complex family of compounds that can be divided into three major groups depending on the structure of the aglycone, which may be a steroid, a steroidal alkaloid, or a triterpenoid. These molecules have been proposed to contribute to plant defense.3 6 Saponins are also exploited as drugs and medicines and for a variety of other purposes.4 Despite the considerable commercial interest in this important group of natural products, little is known about their biosynthesis. This is due in part to the complexity of the molecules, and also to the lack of pathway intermediates for biochemical studies. 

The isoprene pathway produces a diverse range of natural products such as terpenes and steroids. A number of complex biochemical transformations are involved, many of which have been proposed to involve short-lived carbocation intermediates. Two recent studies provide a brief introduction. 

Bryostatins are a unique family of emerging cancer chemotherapeutic candidates isolated from marine bryozoa [457], They were first discovered in the bryozoan Bugula neritina, but problems with supply of sufficient quantities of this natural product hampered the study of this interesting group of marine metabolites for many years. Although the biochemical basis for their therapeutic activity is not known, these macrolactones exhibit high affinities for PKC isoenzymes, compete for the phorbol ester binding site on PKC and stimulate kinase activity in vivo and in vitro. Bryostatin 1, Fig. (54), one member of this family, is a PKC modulator in a variety of tumor systems [458,459], Bryostatin 1 is currently in phase II... 

In 1948, Edmund Hirst moved to Edinburgh University, and Ken returned to Bristol University as Reader in Organic Chemistry. At Bristol, Ken rapidly developed his own carbohydrate-research group and, with great foresight, impressed upon his colleagues the need to apply biochemical methods to the study of natural products, a point of view fully shared by his brilliant assistant (later Professor) Leslie Hough. 

As important as validation studies for synthetic samples are in running a successful discovery program, they are even more important for running natural product samples and especially plant extracts, which are notoriously difficult to run in biochemical or enzyme-based screens. Tannins in particular are responsible for nonspecifically inhibiting activities in such screens. Other nuisance compounds include chlorophyll, melanin, lipids, and waxes. 

Within the last decade, the development of tools at the synthetic, biochemical, proteomic, genomic and immunological levels has opened access to studies that provide an unprecedented look into the complex roles which natural products play. The following sections provide an overview of studies on a select panel of natural products. The goal is not to glorify these studies or their activities but rather to provide an overview of the wondrous modes of natural product action. 

Although the natural products of aromatic PKSs can be much more challenging to predict, their enzymes are much smaller and are often considered to be more tractable to routine heterologous expression, genetic modification and protein structure determination. Indeed, because large modular systems are so much more difficult to work with in vitro, much of what we now know about modular systems has been inferred from direct analogy to biochemical studies of aromatic systems. Aromatic PKSs can now be classified into several specialised families based upon both chemical product type and domain structure. Notably, NRPS analogues of the aromatic PKSs have not been observed. 

It is well known that disulfane-containing compounds, such as proteins, hormones, Upoic acid, enzymes, and other products, occur naturally and many studies on their biochemical role have been published. Protein folding influenced by -S-S bridges of cystine has been studied intensively, and it is generally accepted now that introducing disulfane bonds into proteins thermally stabilizes the folded state. 

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