Chapter 24 Amines 24.8 Synthesize m-ethylphenol from benzene

1. Chapter 24 Amines 24.8 Synthesize m-ethylphenol from benzene (Hint: Use a diazo intermediate = Sandmeyer Rxn)

2. Diazonium Salts: The Sandmeyer Reaction • Primary arylamines react with HNO2, yielding stable arenediazonium salts • The N2 group can be replaced by a nucleophile • Sequence of (1) nitration, (2) reduction, (3) diazotization, and (4) nucleophilic substitution leads to many different products

3. 24.10 Spectroscopy IR -NH2 -NHR -NR2

4. 24.10 Spectroscopy NMR C9H13N

5. Chapter 26: Biomolecules: Amino Acids Peptides and Proteins Chiral C

6. L-glyceraldehyde D-glyceraldehyde Chirality of Amino Acids • Glycine, 2-amino-acetic acid, is achiral • In all the others, the  carbons of the amino acids are centers of chirality • The stereochemical reference for amino acids is the Fischer projection of L-serine • Proteins are derived exclusively from L-amino acids

7. The D-Sugar Family • Correlation is always with D-(+)-glyceraldehyde (R)

8. Draw Fisher diagrams of L-Alanine (R = CH3) and L-cysteine (R = CH2-SH) and assign stereochemistry as R or S

9. Amino Acids: pKa and Isoelectric points

11. Histidine • Contains an imidazole ring that is partially protonated in neutral solution • Only the pyridine-like, doubly bonded nitrogen in histidine is basic. • The pyrrole-like singly bonded nitrogen is nonbasic because its lone pair of electrons is part of the 6  electron aromatic imidazole ring (see Section 24.4).

12. 26.2 Isoelectric Points • In acidic solution, the carboxylate and amine are in their conjugate acid forms, an overall cation • In basic solution, the groups are in their base forms, an overall anion • In neutral solution cation and anion forms are present • This pH where the overall charge is 0 is the isoelectric point, pI

13. Titration Curves of Amino Acids • pKa’s determined from titration curve • If pKa values for an amino acid are known the fractions of each protonation state can be calculated (Henderson-Hasselbach Equation) • pH = pKa – log [A-]/[HA]

14. pI of any amino acid is the average of the two pKa’s that involve the neutral zwitterion

15. 26.3 Synthesis of Amino Acids:Reductive Amination of -Keto Acids • Reaction of an -keto acid with NH3 and a reducing agent (see Section 24.6) produces an -amino acid

16. 26.3 Synthesis of Amino Acids:Chemical Resolution of R,S Amino Acids • Convert amino group into amide and react with a chiral amine to form diastereomeric salts • Separate salts, convert back to the aa by hydrolysis of the amide Enzymic Resolution Enzyme selectively catalyzes hydrolysis of one enantiomer

17. 26.10 Peptide Synthesis • Peptide synthesis requires that different amide bonds must be formed in a desired sequence • The growing chain is protected at the carboxyl terminal and added amino acids are N-protected • After peptide bond formation, N-protection is removed

18. Carboxyl Protecting Groups • Usually converted into methyl or benzyl esters • Removed by mild hydrolysis with aqueous NaOH • Benzyl esters are cleaved by catalytic hydrogenolysis of the weak benzylic C–O bond

19. Amino Group Protection • An amide that is less stable than the protein amide is formed and then cleaved after amide bond formed • The tert-butoxycarbonyl amide (BOC) protecting group is introduced with di-tert-butyl dicarbonate • Removed by brief treatment with trifluoroacetic acid

20. Peptide Coupling • Amides are formed by treating a mixture of an acid and amine with dicyclohexylcarbodiimide (DCC)

21. 26.11 Automated Peptide Synthesis: The Merrifield Solid-Phase Technique

22. 26.13 Protein Structure • The primary structure of a protein is simply the amino acid sequence. • The secondary structure of a protein describes how segments of the peptide backbone orient into a regular pattern. • The tertiary structure describes how the entire protein molecule coils into an overall three-dimensional shape. • The quaternary structure describes how different protein molecules come together to yield large aggregate structures