NOMENCLATURE AND STEREOCHEMISTRY OF STEROIDS

Medicinal chemistry

1. INTRODUCTION
Steroids are a unique class of chemical compounds
found widely in the animal and plant kingdom.
They are biologically active organic compound with four
rings arranged in a specific molecular configuration.
They both occur naturally and man-made versions.

2. NOMENCLATURE OF STEROIDS
Steroids are characterized by the presence of
cyclopentanoperhydrophenanthrene nucleus in their structure
OR it is also known as "Gonane" ring..
The core structure is composed of 17 C-atoms,
bonded in 4 fused rings:
1. Three 6-membered cyclohexane rings,
i.e. Phenanthrene ring (A,B,C)
2. One 5-membered cyclopentane ring (D)
B
D

3. Almost all steroids are derivatives having 17 to 27 C-atoms in their
structure.
There are mostly 5 types of rings in steroids:
1. Gonane: structure with 17 C-atoms
2. Estrane: structure with 18 C-atoms
3. Androstane: structure with 19 C-atoms
4. Pregnane: structure with 21 C-atoms
5. Cholestane: structure with 27 C-atoms
Chalestane

4. Bconfiguration:
Substituent attached to the ring system from above the plane are designated as 9
configuration.
They are denoted by a solid line,
a configuratlon:
Substituent attached to the ring system from below
the plane are designated as a configuration.
They are denoted by a broken or dotted line.
Unknow configuration:
H
f the configuration of the substituent is not known its bond to the nucleus is
represented by a wavy line.

5. In case of presence of double bond present in the 6-membered ring, it will be
indicated by symbol A
ene, 4-ene.
resence uble bond, eg 3
Apart from the 17C ring, there is presence of methy groups at position 10, 13 and
alkyl slde chain at position 17.
. There is substitution of axygen containing functional groups (mainly -OH and C=0)
at position 3, 11, 17, 20, 21

6. there is contractlon of ring of a steroid, this is indicated by the prefix NOR
preceded by a capital letter indicating the ring affected.
A-NOR
It there is enlarement of the ring of a sterold, this is indicated by the prefix HOMO
preceded by a capital letter indicating the ring affected.
B-HOMO S0 pregnane

7. IUPAC Nomenclature
The naming begins with -OH group present on the steroidal moiety above or
below the plane, eg: 179-hydroxy.
t is followed by the name of core ring, eg: Androstane
the ring consists of double bonds, the least number of C-atom having double
bond is writlen after the name of core ring, eg: 3-ene
At last, it is concluded by the ketone group present on the steroidal ring, eg: 3
one.
Examnple: Testosterone
IUPAC name: 17B-hydroxyandrost-4-en-3-one

8. STEREOCHEMISTRY OF STEROIDS
There are six asymmetric carbon atoms s,8,9,10,13, 14 in the nucleus, therefore 64 optically
active forms are possible.
Cholestane, enfrostane and pregnane exist in two conformaions:
1. chair form
2. boat form
5-a-cholestane

9. Chair form is more stable then boat form due to less angle strength, therefore all
cyclohexane ring in steroid nucleus exist in the chair form.
The absolute stereochemistry of the molecule and any substituents is shown with solid
bond (8-configuration) and dotted bond (a-configuration).
The aliphatic side chain at C-17 position is always assumed to be B-configuration.
The term cis and trans are sometimes used to indicate the backbone stereochemistry
between the rings.
example; 5-a-steroid are A/B TRANS.
5-B-steroids are A/B CIS.
5-a-Steroid
AB trans
5-B-Steroid
A/B cis

10. IfAB fusion cis and trans both position possible or position is unknown, it is indicated
by waving lines/bonds.
trans/cis

11. M