Continued from 3S-8. Ring fission and 3S-9. Vitamin D group
3S-10. Additional rings
10.1 Bridged steroids
10.2 Additional ring(s) fused to a steroid
10.3 Spiro union with a steroid
When additional rings are formed within, or on, a steroid nucleus, it is often desirable to retain the steroid stem name, since it implies the stereochemistry of most of the chiral centres. The following recommendations show how such names can be constructed. It will be seen, however, that these names may become cumbersome with more complicated - especially substituted - structures. Recourse to general systematic nomenclature may then be preferable.
The decision whether any one compound shall receive such a modified steroid name or a general systematic name is left to authors and editors in the particular circumstances of each case. Moreover, the requirements of different journals or compendia are not necessarily identical.
3S-10.1. Bridged steroids
Steroids with non-adjacent ring positions linked by a bivalent bridge such as -O-O-, -[CH2]n- (see recommendations A-34 and B-15 in ) are named by the appropriate name and locants to indicate its attachment and or to indicate stereochemistry where necessary. Examples:
(1) In a composite bridge such as epoxymethano in compound 100 the first number of the two locants cited in front of the bridge corresponds to the first cited component of the composite bridge i.e. epoxy (recommendation B-15.2 in ).
(2) With linear bridges such as in compounds 99 and 100 the atoms may be labelled for identification by the superscript number starting from the higher numbered attachment position (see 3S-2.7). It is not recommended that the steroid numbering should be continued with the bridge atoms as the highest used number depends on the steroid skeleton present (recommendation A-34.2 in ).
(3) With a cyclic bridge, such as in compound 101, the numbering of the ring system is retained but each number is primed if needed for identification or further substitution. The name of the bridge includes the attachment positions in front of the name. These locants and any required to name the ring are cited within square brackets without any primes (ref. 3, recommendation B-3.1). Low numbers are preferred for the attachment positions with the lower number nearer the higher numbered attachment position of the steroid.
This system should not normally be extended to adjacent positions, except for simple symmetric bridges, e.g. 102. For other cases see 3S-10.2. Example:
3S-10.2. Additional ring(s) fused to a steroid
Fusion of a carbocyclic or heterocyclic ring component with the maximum number of non-cumulative double bonds to a steroid may be indicated by a modification of fusion nomenclature (see recommendations A-21.3 to A-21.6, B-3.1 to B-3.3 in ). The preferred component is always the steroid. The name of the carbocyclic or heterocyclic attached component is modified to give its prefix form and is cited in front of the steroid name with the nature of the fusion indicated between square brackets. The numbering of the steroid moiety is retained; the atoms of the attached component are identified by primed locants. Those involved in fusion are cited in the order corresponding to those of the steroid. Examples:
(1) There are three changes from the previous recommendations , that are still used by Chemical Abstracts Service index nomenclature:
(i) the unsaturation in the steroid ring due to the fused component is not cited;(2) The current Chemical Abstracts Service index names for 103, 104 and 105 are androst-5-eno[6,5,4-bc]furan, naphth[2',1':2,3]-5-androst-2-ene, and 2-methyl-5-androst-6,16-dieno[17,16-d][1,3]oxathiol--ol respectively.
(ii) the preferred component is always the steroid;
(iii) a terminal a or o of the prefix is not elided.
Fusion locants may be omitted if unnecessary. Example:
If necessary isomers are distinguished by the use of indicated hydrogen (see recommendation A-21.6 in ). If there is a choice of locants due to fusion the unprimed locant is used. Examples:
Note As shown by examples 108 and 110, insertion of the maximum number of non-cumulative double bonds into the attached component is considered to take place after fusion.
3S-10.3. Spiro union with a steroid
Simple spiro systems may be named in an analogous way to bridged steroids (3S-10.1). For example, compound 112 is 3,3-ethylene-5-androstane.
In general a spiro union is cited in the normal way (see recommendations A-41.4, B-10.2 in ). Examples:
1. IUPAC Commission on the Nomenclature of Organic Chemistry (CNOC) and IUPAC-IUB Commission on Biochemical Nomenclature (CBN). The Nomenclature of Steroids, Revised tentative rules, 1967. Arch. Biochem. Biophys. 136, 13-35 (1970), amended 147, 4-7 (1971); Biochem. J. 113, 5-28 (1969), amended 127, 613-616 (1972); Biochemistry, 8, 2227-2242 (1969), amended 10, 4994-4995 (1971); Biochim. Biophys. Acta, 164, 453-486 (1968), amended 248, 387-390 (1971); Eur. J. Biochem. 10, 1-19 (1969), amended 25, 1-3 (1972); Pure Appl. Chem. 31, 285-322 (1972), with amendments incorporated; also pp. 133-153 of , with amendments included.
2. International Union of Biochemistry (1978) Biochemical nomenclature and related documents, The Biochemical Society, London.
3. International Union of Pure and Applied Chemistry, Nomenclature of organic chemistry, Sections A, B, C, D, E, F and H, 1979 Edition, Pergamon Press, Oxford, 1979. Section E appeared also in pp. 1-18 of , and section F in pp. 19-26 of  and in Eur. J. Biochem. 86, 1-8 (1978).
4. A. Butenandt and L. Poschmann, Ber. Dtsch. Chem. Ges. 73, 893-897 (1940); cf. also A. Butenandt, L. Karlson-Poschmann, G. Failer, U. Schiedt and E. Bilkert, Liebigs Ann. Chem. 575, 123-144 (1951).
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).
6. International non-proprietary names (INN) for pharmaceutical substances, cumulative list 6, World Health Organization, 1982.
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