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Stereochemical Lexicon

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

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Stereo-
descriptors Comments
(+)- / d- Optical rotation signs; does not reflect the configuration; Spatial
arrangements of...

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Obsolete terms : falling in disuse Synonyms in current usage
Chiral (stereogenic)
Enantiomers
Constitutional isomers
(+)-;...

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Stereochemical Lexicon

Chemical nomenclature has always been somewhat problematic, and this seems to be particularly true when it comes to stereochemical terms. The nomenclature of the field appears somewhat confused that there is still no universal agreement on some of the most fundamental terms.
The purpose of this presentation is to:
• Point out and discuss the use, misuse, disuse and abuse of
stereochemical lexicon
• Indicate the stereochemical terms that are obsolete
• Inform the new directions in nomenclature system of chiral
drugs

Chemical nomenclature has always been somewhat problematic, and this seems to be particularly true when it comes to stereochemical terms. The nomenclature of the field appears somewhat confused that there is still no universal agreement on some of the most fundamental terms.
The purpose of this presentation is to:
• Point out and discuss the use, misuse, disuse and abuse of
stereochemical lexicon
• Indicate the stereochemical terms that are obsolete
• Inform the new directions in nomenclature system of chiral
drugs

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Stereochemical Lexicon

  1. 1. VALLIAPPAN K Professor of Quality Assurance (Retd.) Department of Pharmacy Annamalai University INDIA 2021 Stereochemical Lexicon 10 min.
  2. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 12. Thanks for your time … Avoid inappropriate use of stereochemical lexicon 2021 Stereochemical Lexicon valliappan Chirally Yours

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