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