1. VALLIAPPAN K
Professor of Quality Assurance (Retd.)
Department of Pharmacy
Annamalai University
INDIA
2021
Stereochemical Lexicon
10 min.

2. Stereo-
descriptors Comments
(+)- / d- Optical rotation signs; does not reflect the configuration; Spatial
arrangements of ligands/substituents around stereogenic center.
(-)- / l-
D- Relative configuration with respect to D-Glyceraldehyde;
L- Relative configuration with respect to L-Glyceraldehyde; Referred
to as Fischer convention
Stereochemical lexicon --- select
D
E
S
C
R
I
P
T
O
R
S
2021
Stereochemical Lexicon
to as Fischer convention
R-
Latin: rectus, right; Absolute configuration as per Cahn-Ingold-
Prelog rule /Sequence rule.
S- Latin: sinister, left; Absolute configuration as per CIP rule.
Cis- / Trans-
Notation employed for describing absolute stereochemistry across
double bonds;
E- / Z-
An extension of cis-trans- isomer notation (which only
describes relative stereochemistry) that can be used to describe double
bonds having two, three or four substituents.

3. Obsolete terms : falling in disuse Synonyms in current usage
Chiral (stereogenic)
Enantiomers
Constitutional isomers
(+)-; dextro-
Dissymmetric
Optical isomers
Structural isomers
d-
Stereochemical lexicon
Stereochemical lexicon --- select
D
E
S
C
R
I
P
T
O
R
S
2021
Stereochemical Lexicon
(+)-; dextro-
(-)- ; levo-
rac- or race-
E-
Z-
d-
l-
dl-
syn-
anti-

4. Misnomer / Syntax error Preferable
Chiral plane Plane of chirality
Chiral axis Axis of chirality
Chiral chromatography Enantioselective chromatography
Chiral stationary phase, Chiral
Stereochemical lexicon --- select
2021
Stereochemical Lexicon
Chiral column
Chiral stationary phase, Chiral
support, Chiral substance
Chiral/Asymmetric synthesis Enantioselective synthesis
Optical purity Enantiomeric purity / excess
Homochiral Enantiopure

5. Objectionable / Abuse Preferred usage
Optical antipode Enantiomer
Optical resolution
Stereochemical lexicon --- select
2021
Stereochemical Lexicon
Resolution of enantiomers /
Separation of enantiomers
Enantiomer resolution
Chiral resolution
Chiral centers/ Multichiral Stereogenic centers

6. Flaw: Used as synonyms which is incorrect
Correct Usage:
 Homochiral: Objects or molecules of the same handedness
(sense of chirality or configuration). Should be reserved for
comparison of two or more objects of like chirality”. Inappropriate
to apply the term to a substance or compound.
Terms: Homochiral and Enantiopure
2021
Stereochemical Lexicon
to apply the term to a substance or compound.
e.g. Left hand of different individuals
R-naproxen, R-ibuprofen, R-warfarin, R- Ketoprofen
 Enantiopure: Configurationally homogeneous sample
(i.e., made up of chiral molecules of the same configuration)
e.g. R-Ibuprofen - pure enantiomer

7. Flaw: Incorrect to describe a molecule containing
> 1 stereogenic center as “Multichiral”
Terms: Chiral centers / Multichiral
2021
Stereochemical Lexicon
Correct Usage:
 Stereogenic center
Molecule is either chiral or achiral.
There are no other choices.

8. Type of drug %
Prefixes
In SIGNS Not to used in SIGNS
Single drugs
N
E
W
D
I
R
E
C
T
I
O
Prefixes for SIGNS
Stereochemically Informative Generic Name System
2021
Stereochemical Lexicon
Enantiomer 25-30 dextro/levo
(+)/(-); (R)/(S); d/l;
D/L
Diastereomers > 1 cis/trans (Z)/(E); syn/anti
Agents with no
stereoisomers
40-50 none
O
N
S

9. Type of drug %
Prefixes
In SIGNS Not to used in
SIGNS
Mixtures
Prefixes for SIGNS
N
E
W
D
I
R
E
C
T
I
O
Stereochemically Informative Generic Name System
2021
Stereochemical Lexicon
Racemates 25-30 rac (±); (R,S); dl
Diastereomeric mixtures >1 diam (Z/E); cis/trans
Mixture of epimers 1-5 mep dia
Simonyi, M., Drug Information Journal, 1994, 28, 533-540.
O
N
S

10. Levofloxacin BNF (No.49, March 2005) only
Levocetrizine BNF (No.49, March 2005) only
Dexketoprofen BNF (No.49, March 2005) only
Racephedrine BP 2011
SIGNS
N
E
W
D
I
R
E
C
T
I
O
2021
Stereochemical Lexicon
Racecadotril BP 2011
Levothyroxine BP 2011
esomeprazole S-Omeprazole
escitalopram S-Citalopram
SIGNS will “tell it like it is” when it comes to stereoisomerism in drugs
O
N
S

11. Levobupivacaine BP 2004
Levodropropizine BP 2011
Levodopa BP 2011
Dextropropoxyphene BP 2011
SIGNS
N
E
W
D
I
R
E
C
T
I
O
2021
Stereochemical Lexicon
Dextropropoxyphene BP 2011
Dexphenfluramine BNF (No.49, March 2005) only
Dextromethorphan (HBr) BP, 2011 (salt form indexed)
SIGNS will “tell it like it is” when it comes to stereoisomerism in drugs
O
N
S

12. Thanks for your time
… Avoid inappropriate use of stereochemical lexicon
2021
Stereochemical Lexicon
valliappan
Chirally Yours