Natural Product Names

Another group of natural products, namely the biologically active lignans of the aryltetralin series - for example, isopodophyllotoxone (2-59), picropodophyllone (2-60), and podophyllotoxin (2-61) (Scheme 2.13) [19] - have also been synthesized using a domino Michael/aldol process. 

Zard and coworkers [32] reported a simple approach to create another group of natural products, namely the lycopodium alkaloids [15]. These authors first investigated the reaction of O-benzoyl-N-allylhydroxylamide 3-60 with tributyltin hydride and ACCN in refluxing toluene, which led (after formation of the N-radical 3-61 in a 5-exo-trig/5-exo-trig cyclization) to the undesired pyrrolidine 3-62 in 48% yield. Nevertheless, a small structural modification, namely the placement of a chlorine atom at the allyl moiety as in 3-63, induced a 5-exo-/G-endo- instead of the 5-exo-/5-... 

Nomenclature based on a parent term with an appended suffix accounts for most natural product names. However, as related compounds are identified, or even when a suffix has to denote multiple functional groups, a variety of modifying terms can be employed. For example, the common prefix nor- denotes the removal of a skeletal atom from the parent structure the loss of two or more skeletal atoms is indicated by combining an appropriate numerical prefix with nor- , e.g., dinor- , trinor- (Giles 1999). Table 1.2 lists additional examples of commonly encountered modifying terms. 

Many of the alkaloids from Veratrum, Zygadenus and related genera are based on the cevane structure 1. The chemistry of the Veratrum alkaloids has been reviewed from time to time both in this treatise (1-3) and elsewhere (4-6). The most recent of these articles was published in 1973, and many new compounds have been discovered since then. Recent years have seen the announcement of many X-ray crystal structure determinations on these stereochemically complex alkaloids. A total synthesis has been reported for only one of the natural products, namely, verticine (7). The work that lead to this notable achievement has been reviewed (8). The pharmacology of both the alkaloids (9-12) and their synthetic derivatives (13) has been reviewed, although not since 1977. This chapter takes a different approach from previous reviews. The chemical reactions used for structure determination and modification are first summarized, but the main part of the chapter is a series of tables which include all the known cevane derivatives, both old and new. This is intended as a reference source for future workers in the field. The literature has been covered to the end of Volume 113 of Chemical Abstracts (1990). 

Four new natural products, namely 5,5"-dichloro-a-terthiophene, 5-chloro-a-terthiophene, 5-acetyl-a-terthio-phene, and 5-carboxyl bithiophene, together with seven known thiophenes were isolated and purified from ethanol extract of roots of Echinops grijisii Hance <2002M1175>. 

Reaction of a naphthalene derivative with chloroacetone gave rise to the natural product named neotanshinlactone, whose biological activity as an anti-tumor agent was evaluated <04JMC5816>. 

The classic sequence of experiments with natural compounds in the twentieth century has been as follows isolation from biological sources, purification, elucidation of molecular structure, and finally total synthesis. These tasks of organic chemistry were fulfilled by the end of the century as far as the major components of higher organisms are concerned. Only compounds that are central to the growth of their tissues are the subject of this book. Many individual compounds of this kind of natural product, namely lipids, steroids, carbohydrates, carotenoids, porphyrins, vitamins, nucleic acids, and proteins, are today commercially available, and their structural and dynamic analysis has reached an accuracy and diversity that leaves little to be desired (Karrer, 1954 Fieser and Feiser, 1960 Tedder et al., 1972 Nuhn, 1981 Fuhrhop, 1982 Beyer and Walter 1988 Fuhrhop and Penzlin, 1994 Mann et al., 1994). 

We also carried out the synthesis of 164, the C(ll)-epimer of 160. Epimerization of this carbon was carried out by selective hydrogenation of the a-methylene lactone 162 and this gave 163, which was transformed into compound 164 by a similar sequence. However, compound 164 again has different spectroscopic data in comparison with the natural product. Consequently, the structures of the natural products named herbolide E and herbolide I should be revised. 

ABSTRACT This article describes physiological properties of two classes of natural products, namely cholesterol oxides and dehydroepiandrosterone (DHEA). The cholesterol oxides, also called oxysterols, are autoxidation products of cholesterol. Dehydroepiandrosterone and its sulfate DHEAS are formed mainly in the adrenals. The biological activities of these compounds are utilized to construct the two following hypotheses. 

SSA constitutes a methyl ketal derivative of a natural product named FR901464 and was originally isolated from a Pseudomonas sp. fermentation broth [24, 25]. Before identification of the molecule s true mechanism, FR901464 had already attracted attention as a potent activator of viral promoters, as well as having visible antitumor activity. It inhibited the growth of various cancer cell lines at low nanomolar concentrations and extended the life span of tumor-bearing mice. 

The aim of one section of this Ph.D. project is to further extend the scope of the ZrCl4-catalysed deprotection/cyclisation protocol in the synthesis of analogues of the marine natural products (+)-tanikolide (19) and malyngolide (20) (Fig. 1.9). It was also hoped to expand the ZiCLi-catalysed deprotection/cyclisation sequence to the synthesis of y-lactone-containing natural products, namely (+)-mmicatacin (21) and (-)-muricatacin (22). 

A detailed interpretation of LC/ H-NMR in combination with LC/UV-DAD, LC/MS, and chemotax-onomical data (see the case of 3 in Figure 5) enables the identification of three known lignanes ( —)-phylligenin (3), ( —)-eudesmin (4), ( —)-epieudesmin (5) as well as polycerasoidol (6). Compound (7) could be completely identified based on online data and was finally characterized as a new polyacetylenic natural product named oropheic acid (7). This example also demonstrates the use of LC/UV LC/MS and LC/NMR in phytochemical analysis known natural products can be dereplicated by comparison... 

Several studies were dedicated to the construction of the tetrahydropy-ran scaffold in the total synthesis of natural products, namely (—)-brevisamide (130BC6751), (—)-blepharocalyxin D (13OL2046), bryostatins... 

At that time, we strived for the first total synthesis of a polyunsaturated natural product named xerulinic acid (22 Scheme 4). We envisaged using the hexatriene-l,6-distannane trans,trans,trans-lS (Fig. 5) as a Cg linchpin for joining the Z-configured y-(hromomethylidene)butenolide 20 and the polyunsaturated bromoalkyne 23 by sequential Stille couplings. 

The handed book is constmcted in the logic of presenting the parallel development of biosynthesis and organic methodology and how these can be apphed in efficient syntheses of natural products. The book is divided into four sections each representing the four major biosynthetic pathways of natural products, namely, acetate, mevalonate, shikimate biosynthetic pathways, and the mixed biosynthetic pathways... 

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