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Racemization Outline

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Intro

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In chemistry, racemization refers to the conversion of an enantiomerically pure mixture (one where only one enantiomer is present) into a mixture where more than one of the enantiomers are present. An enantiomer, also known as an optical isomer, refers to a stereoisomer of a pair of molecules that are nonsuperposable mirror images of each other. If the racemization results in a mixture where the D and L enantiomers are present in equal quantities, the resulting sample is described as racemic, a racemic mixture, or a racemate.[3][1]

Discovery of Optical Activity

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In 1843, Louis Pasteur discovered optical activity in paratartaric, or racemic, acid found in grape wine. He was able to separate two enantiomer crystals that rotated polarized light in opposite directions.[1]

Thalidomide

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In general, only one form of a chiral molecule will participate in biochemical reactions while the other simply does not participate or can cause side-effects. Of note, the L form of amino acids and the D form of sugars (primarily glucose) are usually the biologically reactive form. This is due to the fact that many biological molecules are chiral and thus the reactions between specific enantiomers produce pure stereoisomers.[2]

Additionally, many psychotropic drugs show differing activity or efficacy between isomers, e.g. amphetamine is often dispensed as racemic salts while the more active dextroamphetamine is reserved for refractory cases or more severe indications; another example is methadone, of which one isomer has activity as an opioid agonist and the other as an NMDA antagonist.

Racemization of pharmaceutical drugs, however, can occur in vivo. An example is thalidomide: its (R) enantiomer is effective against morning sickness, while the (S) enantiomer is teratogenic, causing birth defects when taken in the first trimester of pregnancy. If only one enantiomer is administered to a human subject, both forms may be found later in the blood serum.[4] The drug is therefore not considered safe for use by women of child-bearing age, and while it has other uses, its use is tightly controlled.[5][6] Thalidomide can be used to treat multiple myeloma. [7]??? Another commonly used drug is ibuprofen which is only anti-inflammatory as one enantiomer while the other is biologically inert. Likewise, only one stereoisomer in Citalopram (Celexa), an antidepressant which inhibits serotonin reuptake, is active. The The study of enantiomers in the pharmaceutical industry is termed chiral organic synthesis.[2][1]

Also notable is the fact that all amino acid residues exist in the L form. However, bacteria produce D-amino acid residues that polymerize into short polypeptides which can be found in bacterial cell walls. These polypeptides are less digestible by peptidases and are synthesized by bacterial enzymes instead of mRNA translation which would normally produce L-amino acids.[2]

FIGURE 1– 24 Stereoisomers have different effects in humans. ( a) Two stereoisomers of carvone: ( R)- carvone ( isolated from spearmint oil) has the characteristic fragrance of spear-mint; ( S)- carvone ( from caraway seed oil) smells like caraway. ( b) Aspartame, the artifi-cial sweetener sold under the trade name NutraSweet, is easily distinguishable by taste receptors from its bitter- tasting stereoisomer, although the two differ only in the configura-tion at one of the two chiral carbon atoms. ( c) The antidepressant medication citalopram ( trade name Celexa), a selective serotonin reuptake inhibitor, is a racemic mixture of these two steroisomers, but only ( S)- citalopram has the therapeutic effect. A stereochemically pure preparation of ( S)- citalopram ( escitalopram oxalate) is sold under the trade name Lexapro. As you might predict, the effective dose of Lexapro is one- half the effective dose of Celexa.[1]

The amino acid alanine exists only as the L-Alanine form.

Amino Acid dating [[1]]

Amino Acid edits

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  • Template

[Amino Acid(Common)] (abbreviated as [XXX] or [X]; encoded by the codons [codon list here]) is an ɑ-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated -+NH3 form under biological conditions), an α-carboxylic acid group (which is in the deprotonated –COO- form under biological conditions), and a side chain [Functional group], classifying it as a [polar/nonpolar/charged(at physiological pH), aromatic/aliphatic] amino acid. It is [essential/non-essential/semi-essential] in humans, meaning the body [cannot synthesize it and thus it must be obtained from the diet/can synthesize it/can synthesize it from the essential amino acid [another amino acid]].

Unique/interesting info about that amino acid.

  • Leucine

Leucine (abbreviated as Leu or L; encoded by the six codons UUA, UUG, CUU, CUC, CUA, and CUG) is an ɑ-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated -+NH3 form under biological conditions), an α-carboxylic acid group (which is in the deprotonated –COO- form under biological conditions), and an isobutyl side chain, classifying it as a nonpolar(at physiological pH) amino acid. It is essential in humans, meaning the body cannot synthesize it and thus it must be obtained from the diet.

Leucine is a major component of the subunits in ferritin, astacin, and other 'buffer' proteins.

Leucine (abbreviated as Leu or L) is an essential, branched-chain α-amino acid, classified hydrophobic due to the isobutyl side chain. Its structural formula is HO2CCH(NH2)CH2CH(CH3)2. L-Leucine is encoded by six codons (UUA, UUG, CUU, CUC, CUA, and CUG) and is a major component of the subunits in ferritin, astacin, and other 'buffer' proteins.

  • Glutamine

Glutamine (abbreviated as Gln or Q; encoded by the codons CAA and CAG) is an ɑ-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated -+NH3 form under biological conditions), an α-carboxylic acid group (which is in the deprotonated –COO- form under biological conditions), and a side chain amide which replaces the side-chain hydroxyl of glutamic acid with an amine functional group, classifying it as a charge neutral, polar(at physiological pH) amino acid. It is non-essential and conditionally essential in humans, meaning the body can usually synthesize sufficient amounts of it, but in some instances of stress, the body's demand for glutamine increases and glutamine must be obtained from the diet.[8][9]

In human blood, glutamine is the most abundant free amino acid, with a concentration of about 500–900 µmol/l.[10]

Glutamine (abbreviated as Gln or Q, and often called L-glutamine) is one of the 20 amino acids encoded by the standard genetic code. It is considered conditionally essential.[8] In human blood, glutamine is the most abundant free amino acid, with a concentration of about 500–900 µmol/l.[10] The side-chain is an amide formed by replacing the side-chain hydroxyl of glutamic acid with an amine functional group, making it the amide of glutamic acid. Gln's codons are CAA and CAG.

Sources

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Lehninger citation [1]

Voet, Voet, Pratt citation [2]

Racemization [11]

Enantiomers [12]

Enantiomeric separation [13]

Racemic Alanine [14]


References

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  1. ^ a b c d e f g h i j Nelson, David L.; Cox, Michael M. (2013). Lehninger Principles of Biochemistry (6th ed.). New York: W.H. Freeman. ISBN 978-1429234146.
  2. ^ a b c d e Voet, Donald; Voet, Judith G.; Pratt, Charlotte W. (2013). Fundamentals of Biochemistry: Life at the Molecular Level (4th ed.). Hoboken, NJ: Wiley. ISBN 978-0470547847.
  3. ^ Introduction to Organic Chemistry (3rd ed.). Maxwell MacMillan. 1985. pp. 122–124. ISBN 0029467209. {{cite book}}: Unknown parameter |authors= ignored (help)
  4. ^ Teo SK, Colburn WA, Tracewell WG, Kook KA, Stirling DI, Jaworsky MS, Scheffler MA, Thomas SD, Laskin OL (2004). "Clinical pharmacokinetics of thalidomide". Clin Pharmacokinet. 43 (5): 311–327. doi:10.2165/00003088-200443050-00004. PMID 15080764. S2CID 37728304.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  5. ^ Sheryl Gay Stolberg (17 July 1998). "Thalidomide Approved to Treat Leprosy, With Other Uses Seen". New York Times. Retrieved 8 January 2012.
  6. ^ "Use of thalidomide in leprosy". WHO:leprosy elimination. WHO. Retrieved 22 April 2010.
  7. ^ Reddy, K. Chandra Sekhara; Kasiviswanath, I.V. (January 2013). "Racimisation of (R)–Alpha–Ethyl-2-Oxo-1-Pyrrolidine Acetic acid with Thionyl Chloride". International Journal for Pharmaceutical Research Scholars (IJPRS). 2 (1): 45–48.
  8. ^ a b Dietary Reference Intakes: The Essential Guide to Nutrient Requirements, published by the Institute of Medicine's Food and Nutrition Board, currently available online at http://fnic.nal.usda.gov/dietary-guidance/dietary-reference-intakes/dri-reports
  9. ^ Lacey, JM; Wilmore, DW (1990 Aug). "Is glutamine a conditionally essential amino acid?". Nutrition Reviews. 48 (8): 297–309. doi:10.1111/j.1753-4887.1990.tb02967.x. PMID 2080048. {{cite journal}}: Check date values in: |date= (help)
  10. ^ a b Brosnan, John T. (June 2003). "Interorgan amino acid transport and its regulation". J. Nutr. 133 (6 Suppl 1): 2068S–2072S. doi:10.1093/jn/133.6.2068S. PMID 12771367. 
  11. ^ Gross, Erhard; Meienhofer, Johannes (2014). Major Methods of Peptide Bond Formation: The Peptides Analysis, Synthesis, Biology, Volume 1. Elsevier. ISBN 978-1483217963.
  12. ^ Lorenz, Heike; Seidel-Morgenstern, Andreas (17 January 2014). "Processes To Separate Enantiomers". Angew. Chem. Int. Ed. 53 (5): 1218–1250. doi:10.1002/anie.201302823. hdl:11858/00-001M-0000-0015-384D-F. PMID 24442686.
  13. ^ Bueno-Perez, Rocio; Martin-Calvo, Ana; Gómez-Álvarez, Paula; Gutiérrez-Sevillano, Juan J.; Merkling, Patrick J.; Vlugt, Thijs J. H.; van Erp, Titis S.; Dubbeldam, David; Calero, Sofia (24 July 2014). "Enantioselective adsorption of ibuprofen and lysine in metal–organic frameworks". The Royal Society of Chemistry. 50: 10849–10852.
  14. ^ Cao, Hai; Zhu, Xuefeng; Liu, Minghua (11 March 2013). "Self-Assembly of Racemic Alanine Derivatives: Unexpected Chiral Twist and Enhanced Capacity for the Discrimination of Chiral Species". Angewandte Chemie International Edition. 52 (15): 4122–4126. doi:10.1002/anie.201300444. PMID 23495092.
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