Continued from 3S-7. Ring contraction and expansion
3S-8. Ring fission
8.1 Use of the prefix seco-References for this section
8.2 Use of and in seco-compounds
3S-9. Vitamin D group
9.1 Trivial names
9.2 Modifications of the triene system
9.3 Modification of the side chain
9.4 Additional hydroxyl groups
3S-8.1. Use of the prefix seco-
Fission of a ring, with addition of a hydrogen atom at each terminal group thus created, is indicated by the prefix seco-, the original steroid numbering being retained. (If more than one ring is opened, general systematic nomenclature may be preferable. The principles of Note 2 to Recommendation 3S-7.4 apply also to seco-steroids.) Examples:
3S-8.2. Use of and in seco-compounds
The stereochemical steroid descriptors and apply only when the remaining rings of a seco-compound are oriented as in the parent steroid, but not to alternative conformations (see formulae 92a and 92b). It is therefore recommended that after fission of ring B the stereochemistry of substituents on ring A is indicated by the R,S convention and and are restricted to rings C and D. Likewise after fission of ring C the stereochemistry of substituents on ring D is indicated by the R,S convention and and are restricted to rings A and B.
3S-9. VITAMIN D GROUP
By far the most important seco-steroids are the D vitamins and their derivatives. They can be named according to Recommendation 3S-8.1, but this results in very cumbersome names. For this reason and for the benefit of biochemists, a set of trivial names has been proposed , which can also be used as stem names for modified compounds. These names are permissive, not compulsory; authors may prefer to use the systematic seco-steroid names, which may indeed be more convenient for complicated structures.
Another reason for the revision of the vitamin D nomenclature is the confusion arising from the application of the steroid descriptors and . According to 3S-8.2, the R,S system should be used to describe the stereochemistry of substituents in ring A. Likewise, the geometry of the double bonds should be assigned by the E,Z system.
The names of the principal members of the vitamin D group are given in Table 3.
3S-9.1. Trivial names
The compound 92, also known as vitamin D3 or cholecalciferol, is named calciol. The name implies the stereochemistry shown, which is 3S,5Z,7E. The name should only be used for the compound with a hydroxyl group at C-3 with the same orientation as in 3-hydroxy steroids. Compound 93 is named calcidiol, and compound 94 is calcitriol. Some more trivial names are listed in Table 3, together with the systematic steroid names.
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Table 3. Nomenclature for vitamin D compounds
|Current trivial name||Recommended trivial name||Systematic steroid name|
|Cholecalciferol||calciol or cholecalciferol (92)||(5Z,7E)-(3S)-9,10-secocholesta-5,7,10(19)-trien-3-ol|
|Ergocalciferol||ercalciol or ergocalciferol||(5Z,7E,22E)-(3S)-9,10-secoergosta-5,7,10(19),22-tetren-3-ol a|
|22,23-dihydroergocalciferol||(24S)-methylcalciol or 22,23-dihydroercalciol||(5Z,7E)-(3S)-9,10-secoergosta-5,7,10(19)-trien-3-ol b|
|Isovitamin D3||(5E)-isocalciol (96)||(5E,7E)-(3S)-9,10-secocholesta-1(10),5,7-trien-3-ol|
(1) The names calciol, calcidiol, calcitriol imply not only the stereochemistry but also the location of the hydroxyl group(s). Compounds with hydroxyl groups in other positions must be named either according to 3S-9.4 (below), or in the usual semisystematic way applying Recommendation 3S-8.1.
(2) The trivial names cholecalciferol and ergocalciferol are retained. They should, however, not be used for naming metabolites.
(3) Because of the nature of the sequence rule, it is not possible to transfer R or S from one compound to its derivatives. Calciol is a 3S compound but calcitriol is a 3R compound though the absolute configuration of the hydroxyl group at C-3 is not changed.
3S-9.2. Modifications of the triene system
The prefix ta- (derived from tachysterol) indicates a change of the triene system from (5Z,7E)-5,7,10(19) to (6E)-5(10),6,8 as in tacalciol 95a and 95b.
The prefix iso- (derived from isovitamin D) when applied to calciol changes the location of the triene system to 1(10),5,7 with 7E configuration implied; the geometry at position 5, when known, must be specified by 5E 96 or 5Z 97.
3S-9.3. Modification of the side chain
The prefix er- (derived from ergosterol) is used to indicate the side chain of the vitamin D2 or ergocalciferol. This prefix implies the 22E,24R configuration as given in formula 98 unless otherwise specified.
3S-9.4. Additional hydroxyl groups
Additional hydroxyl groups cannot be indicated by modification of the suffix -ol, -diol, -triol, -tetrol, since these have definite meanings (see Table 3). They can, however, be added as prefix, e.g. (1S)-1-hydroxycalciol, 16-hydroxycalciol. If possible, the full stereochemistry should be given, e.g. (25R)-26-hydroxycalciol. For other modifications and more detailed discussion of the nomenclature problems in the vitamin D field, the reader is referred to the original document .
5. IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN), Nomenclature of vitamin D. Recommendations 1981. Arch. Biochem. Biophys. 218, 342-346 (1982); Endokrinol. Inform. 1982(2), 53-62; Eur. J. Biochem. 124, 223-227 (1982); Mol. Cell. Biochem. 49, 177-181 (1982); Pure Appl. Chem. 54, 1511-1516 (1982).
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