peptide - Chem 234 Organic Chemistry I I Professor Duncan...

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Unformatted text preview: Chem 234 Organic Chemistry I I Professor Duncan J. Wardrop University of I llinois at Spring 2004 H N N Cl O N 3 HO N NH O O CH 3 N H H N Br O O Br N O O N H H H H H O MeO O O OMe OMe O OMe O HO O O O O HO N CO 2 H S O HN NH H H H HO N N CF 3 CH 3 H 2 NSO 2 Cl Cl Cl OH Exam Conflicts Please contact me by next Tuesday if you require a makeup final exam. Failure to do so will delay your exam result and, potentially, your ability to graduate Chapter 27 Amino Acids, Peptides, and Proteins Topics Covered: 1. Peptides: Nomenclature, Geometry & 1 Structure 2. Structural Determination of Peptides 3. Solution Phase Synthesis of Peptides 4. Solid Phase Synthesis of Peptides 5. Peptides and Proteins: 2 and 3 Structure Todays Lecture 27.7 Peptides What is a Peptide? Peptides are compounds in which an amide bond links the amino group of one -amino acid and the carboxyl group of another. O N N R 4 H H O R 3 N R 2 R 1 H An amide bond of this type is often referred to as a peptide bond. Dipeptides are Formed from the Condensation of Two Amino Acid Residues O O N H H 3 C H H H O O N H H H H H L- Alanine Glycine Alanylglycine is the Dipeptide derived from Alanine and Glycine O N N H H 3 C H H H Alanylglycine H O O O N N H H H H O O CH 3 I n alanylglycine, two - amino acids are joined by a peptide bond. I ts a dipeptide . Dipeptides Possess Directionality O N N H H H H O O CH 3 AlaGly AlaGly AG AG N-Terminus N-Terminus C-Terminus C-Terminus Ala-Gly is a Constitutional I somer of Gly- Ala Alanylglycine Alanylglycine AlaGly AlaGly AG AG O N N H H H H O O CH 3 R O N N H H H H O O CH 3 R Glycylalanine Glycylalanine GlyAla GlyAla GA GA As constitutional isomers, these molecules potentially have different physical, chiroptical, spectroscopic and biological properties Geometry of Peptides The defining structural feature of peptides is the planarity of the secondary amide unit, which arises from interaction of the nitrogen lone pair and the orbital of the C=O bond. N O N O Delocalization of the non-bonding electrons on nitrogen into the carbonyl group also raises the rotation barrier of the acyl carbon-nitrogen bond. the hybridization adopted by nitrogen depends upon the nature of the N-substituents - compare methylamine and formamide. Amines & Amides - Geometry at Nitrogen Lone Pair H N H H H H sp 3- hydridized tetrahedral C N H H H H H methylamine O C N H H H Lone Pair sp 2- hydridized planar N H H O H formamide The peptide bond is characterized by a planar geometry. O N N H H H H O O CH 3 R Geometry of Ala-Gly Peptide Nomenclature Peptides are classified according to the number of amino acids linked together. Dipeptides Two residues Tripeptides Three residues Tetrapeptides Four residues Leucine enkephalin is an example of a pentapeptide. TyrGlyGlyPheLeu YGGFL Leucine Enkephalin is a Pentapeptide O N N H H H H N O NH H N O H N O H O O O N N H H H H N O NH H N O H N O H O O Oxytocin is a Cyclic Nonapeptide Oxytocin is a cyclic nonapeptide.Oxytocin is a cyclic nonapeptide....
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This note was uploaded on 09/30/2011 for the course CHEM ORGANIC CH taught by Professor Dotsevisogah during the Spring '09 term at Cornell University (Engineering School).

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peptide - Chem 234 Organic Chemistry I I Professor Duncan...

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