2.nomenclature of steroids
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Transcript of 2.nomenclature of steroids
Nomenclature of steroids
Prepared byDr. N.GOPINATHAN
ASSISTANT PROFESSORDEPARTMENT OF PHARMACEUTICAL CHEMISTRY
FACULTY OF PHARMACYSRI RAMACHANDRA UNIVERSITY
CHENNAI-116TAMILNADU
Nomenclature• Designated by trivial names.
• Discard the names in favor of systematic names which are approved by the International union of pure and applied Chemistry
NUCLEUS AND NUMBERING
β configuration
Substituent attached to the ring system from above are designated as β preferably thickened
α configurationSubstituent attached to the ring system from below are designated as α preferably brokened or dotted
Unknown configuration
If the configuration of the substituent is not known its bond to the nucleus is represented by a wavy line and it is indicated by
•One should specify the stereo chemical configuration of the steroid
If some of the carbon atoms are missing in steroid, the numbering of the remainder will not change in order to illustrate the above rules
NORMAL ALTERED
Suppose angular methyl group is absent then also the numbering wont change
If the side chain does not contain a methylene group. This is indicated by the prefix NOR preceded by the number of carbon atom that has disappeared
Mentioned as 21 Nor
If the steroid does not contain angular methyl group this is again indicated by the prefix NOR preceded by the number in designating the methyl group
If contraction of ring of a steroid, this is again indicated by the prefix NOR preceded by a small capital letter indicating the ring affected
It is mentioned as A nor
If the enlargement of the ring of a steroid this is indicated by the prefix HOMO precede by a small capital letter indicating the ring affected
CH3
B-HOMO 5 beta pregnane
If ring fission in a steroid with the addition of a hydrogen atom to each new terminal group, this is indicated by the numbers showing the position of the bond broken, followed by the prefix seco
O
OH
O
OH
2,3 Seco -5 β androstane 2,3 dioic acid
If steroid contain a three membered ring, this is indicated by the prefix cyclo preceded by the number of positions concerned
CH3
CH3
CH3
Due to introduction of the above mentioned rules of nomenclature, some names are employed in the earlier literature have been rejected and replaced by new names.
Coprostane is now called as 5β chloestaneIso compounds are now called as cyclo compounds
• Methyl groups are normally present at C10 and C13.
• Alkyl side chain at C-17• Sterols- • OH at C-3
If one methyl group is attached to C-25. It is assigned the number 26.
If both are substituted that carrying the substituent cites first in the alphabetical order is assigned the lowest number
When the configuration is not known for one or more centre it is indicated by greek letter ε prefixed by the appropriate locant [s]
If one of the bridge head hydrogen atom is replaced it may be desirable to restate the stereochemistry9 α fluro, 5 α pregnaneinstead of9fluro 5 α pregnane
5 α pregnane
5 α Cholane
5 α Cholestane
• Unsaturation is indicated by changing ane to ene if it contains one double bond, diene if it contains two double bond and triene if it has three double bond.
The symbol used to designate a C=C bond
• If C=C is between 4 and 5 referred as 4
• If C=C is between 5 and 10 designated as 5
• If the double bond is not between sequentially numbered carbon, both the carbons are indicated in the name.
When an additional ring is formed by means of direct line between any two carbon atoms of steroid or attaches side chain. The name of the steroid is prefixed by cyclo. This is prefixed by number of positions of lines given by the new bond. Greek letter α, β, ε denotes the configuration associates with new bond
3 α, 5 - cyclo
Naturally occuring steroids contain one or more additional heterocyclic ring fused or attached to ring D formed by the modification of the side chain
OO
Cardenolide-lactone-5 member
Bufanolide – pyranone-6 member
• Lengthening of side chain by insertion of one or more CH2 group indicated by prefix HOMO
Removal of terminal ring with addition of hydrogen atom at junction where the adjacent ring is indicated by the prefix DES followed by italic capital letter designated the ring
Des A
• Alternative application of nor and homo to the same molecule the abeo system is used
Abeo
The systematic names are based on the stem name which in turn based on the hydrocarbon system
Cholestane with 27 carbon
CH3
CH3
CH3
CH3
CH3
Pregnane with 21 carbon
CH3
CH3CH3
CH3
CH3 CH3
Androstane- carbon 19
Estrane – carbon 18
Gonane – carbon 17
Stereo chemistry
The stereo chemistry of the rings markedly affects biological activity of a given class of steroidsThere are six asymmetric carbon atoms 5,8,9,10,13,14 in the nucleus.Therefore 64 optically active forms are possible
• It can exist in two conformations namely chair form and boat form.
• Chair conformation is more stable than boat conformation due to less angle strain.
• Hence all cyclohexane rings exist in chair form
• Hydrogen or functional groups on the β side of the molecule are denoted by solid lines and the α side is denoted by dotted lines