Natural products nomenclature

The (non-detachable) prefix carba- signifies replacement of a heteroatom by carbon in general natural product nomenclature [26], and may be applied to replacement of the hemiacetal ring oxygen in carbohydrates if there is a desire to stress homomorphic relationships. If the original heteroatom is unnumbered, the new carbon atom is assigned the locant of the non-anomeric adjacent skeletal atom, with suffix a . 

Table 1.1 Examples of natural product nomenclature suffix usage...

Subtractive. Loss of certain atoms or groups from a parent structure, e.g., A-demethylnitidine. Relatively common in natural product nomenclature, rare in mainstream organic chemistry. 

The Joint lUPAC/IUBMB Commission has pubHshed many recommendations dealing with the nomenclature of natural products (72), steroids... 

Natural products biosynthesis, 1, 83-109 fused oxirane rings, 7, 192 fused thiirane rings, 7, 192-193 as insecticides, 1, 198 nomenclature, 1, 28-31 oxiranes, 7, 120 as pharmaceuticals, 1, I46-I56 pyridine derivatives... 

Many names in common use for heteropolycycles provide little or no information about structure. Most such names were introduced long before any serious attempts were made to systematize nomenclature, and although more systematic equivalents can now be coined in many cases (for example, indole can be named benz[f)]azole or 1-azacyclopentabenzene), it is likely that the use of a substantial residue of trivial names will continue. However, one would not expect many new trivial names to be introduced in the future, except in the natural product area (see Section 1.02.4). 

Note. In carbohydrate nomenclature, substitution at a heteroatom is normally indicated by citing the locant of the attached carbon atom, followed by a hyphen, and then the italicized heteroatom element symbol, e.g. 2-0-methyl, 5-N-acetyl. Substituents on the same kind of heteroatom are grouped (e.g. 2,3,4-tri-0-methy 1), and substituents of the same kind are cited in alphabetical order of heteroatoms (e.g. 5-N-acetyl-4,8,9-tri-0-acetyl). The alternative format with superscript numerical locants (e.g, N5,(/,(), ( -tetraacetyl), used in some other areas of natural product chemistry, is unusual in carbohydrate names. 

Note. General natural product fusion nomenclature [26] would require the carbohydrate portion to be cited last (e.g. oxazologlucopyranose), whereas it is cited first here and in the literature. 

The intense need for herbal information in response to consumer interest in natural products was an acute reminder that information and knowledge generated locally have an international role. Confusion created by multiple names and unreliable nomenclature and classification of natural products mirrors problems encountered with drug nomenclature in the 1960s. Our information deficit in this area is still large. Chapter 24 presents a discussion of natural products. 

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. 

International Union of Pure and Applied Chemistry (IUPAC). Nomenclature of organic chemistry. Section F natural products and related compounds (Recommendations 1976). IUPAC Information Bulletin, Appendices on provisional nomenclature, symbols, terminology, and conventions, No. 53, December 1976. [Also in Eur J Biochem 86 1-8 (1978)]... 

The Diels-Alder reaction is one of the most important carbon-carbon bond forming reactions,521 522 which is particularly useful in the synthesis of natural products. Examples of practical significance of the cycloaddition of hydrocarbons, however, are also known. Discovered in 1928 by Diels and Alder,523 it is a reaction between a conjugated diene and a dienophile (alkene, alkyne) to form a six-membered carbo-cyclic ring. The Diels-Alder reaction is a reversible, thermally allowed pericyclic transformation or, according to the Woodward-Hoffmann nomenclature,524 a [4 + 2]-cycloaddition. The prototype reaction is the transformation between 1,3-butadiene and ethylene to give cyclohexene ... 

Current nomenclature for heterocyclic natural products is to a large extent trivially based however, some degree of semisystematization has been achieved. The following notes will indicate briefly the nature of the systems available and their sources, where appropriate. 

The Joint IUPAC/IUBMB Commission has published many recommendations dealing wiLh the nomenclature of natural products. The IUBMB Commission on Nomenclature has also issued a number of recommendations dealing with areas of a more biochemical nature and for naming enzymes. 

The saccharides have long and awkward names by the IUPAC system, consequently a highly specialized nomenclature system has been developed for carbohydrates. Because this system (and those like it for other natural products) is unlikely to be replaced by more systematic names, you will find it necessary to memorize some names and structures. It will help you to remember the meaning of names such as aldopentose and ketohexose, and to learn the names and details of the structures of glucose, fructose, and ribose. For the rest of the carbohydrates, the nonspecialist needs only to remember the kind of compounds that they are. 

Steroids. Steroids are important natural products that have a special nomenclature. They typically consist of three fused 6-membered rings and a four fused 5-membered ring. The... 

One particular domain in which the alternate method of naming is of significance is that of natural products (perhaps, because of the occurrence of many ring assemblages). Note that this is a domain which, because of the complexity of the IUPAC nomenclature, has opted to formulate its own set of parochial rules of nomenclature, in much the same way as the organic chemistry community formulated IUPAC nomenclature to include 35 "basis" aromatic compounds on which all other "comparable" compounds were to be named [18], This is in contradistinction to various systematic approach, such as a geometry-based proposals for the fusion of benzene modules [19] and for general arenes [20],... 

In the now well-entrenched sub-discipline ("fiefdom") of natural products, Buckingham [21] advises "There is one major departure from recommended IUPAC nomenclature rules that is made by almost all those publishing in natural products... that each name shall have only one principal group." In other words, a major subset of "organic" chemists do not subscribe to the official nomenclature of their own domain, and a uniform... 

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