Carotenoid Nomenclature

Trivial names were used because the structures were not established and the number was small. With more than 600 carotenoids of proven structure now known there is still a need for trivial names, but there is also a need for more precise names that follow a chemical convention.

Under trivial names the carotenoids are generally grouped as carotenes (hydrocarbons) and the oxygen-containing compounds as xanthophylls. Some of the carotenes' names are preceded by a Greek letter (eg, [i, e), and others have names denoting the source (lycopene tomato). Some are a combination such as yS-zeacarotene and a-zeacarotene. Here the ring double-bond position and the source (maize) are indicated.

Table 1. Distribution of Natural Coloring Matter

Food Heme Carotenoids Chlorophyll Betalains Anthocyanins Flavonoids Caramel Melanina

Xanthophylls are pigments that contain hydroxyl, car-bonyl, epoxide, ester, and carboxylic acid groups. The convention today is to indicate the source and add the suffix xanthin (eg, tunaxanthin). Some of the older trivial names such as lutein denoted their yellow color. Structural features are indicated by the prefix iso, as in isozeaxanthin; the hydroxyl group in zeaxanthin is in the three position, and it is in the four position in isozeaxanthin cis-Lycopene would indicate a departure from the expected all-trans structure.

In recent years an attempt has been made to limit the number of trivial names by building on a known name such as /?-carotene. Thus astaxanthin might be 3,3'dihydroxy-4,4 ' -diketo-/?-carotene.

The systematic method of carotenoid nomenclature uses the IUPAC convention (14-15) (Fig. 1). The advantage is that any carotenoid can be exactly named, including chiral centers. The disadvantage is that the name for a complicated compound can take two or three lines, whereas the trivial name is a single work (eg, fucoxanthin). In the IUPAC system the central chain is assumed to be unsaturated and all-trans. Any departure from this structure is specified. Thus yS-carotene is ft, ^-carotene. The term nor indicates that a methyl is missing, and seco indicates a break in the ring structure such as 5,6, SECO, fS, fi-carotene-5,6-dione (semi-/?-carotenone). The change in the hydrogénation level to form saturated positions as well as acetylenes and aliénés can be designated by hydro and de-hydro.

Oxygenated derivatives of carotenoid hydrocarbons are named by use of suffixes and prefixes according to the rules of general chemical nomenclature. The principal group is chosen and is cited by use of a suffix, and the other groups are cited as prefixes. The sequence is as follows: carboxylic acid, ester of carotenoid acid, aldehyde, ketone, alcohol, ester of carotenoid alcohol, and epoxide. Apo-carotenoids are found naturally as well as occurring synthetically. The apo designates where the parent compound has been



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