Ch 28 - Amino Acids & Proteins

Question 0

Forms of a.a. as pH ⬆?

Answer 0

Low pH: COOH & NH3+
Middle pH: COO- & NH3+
High pH: COO- & NH2

Question 1

Drawing D, L a.a.?

Answer 1

Keep NH2 & COOH in plane, H in front, R (side chain) behind
• L (S, natural): COOH on right
• D: COOH on left

Question 2

General steps to separate a.a. enantiomers? (resolution)

Answer 2

1) convert pair of enantiomers ➡ diastereomers
2) separate diastereomers
3) re-convert back to enantiomers

Question 3

Reagents used to resolve amino acids?

Answer 3

1) convert a.a. ➡ N-acetyl a.a. w/Ac2O
2) rxt COOH w/(R)-alpha-methylbenzylamine
3) separate ➡ rxt w/HCl to reconvert to enantiomers

Question 4

What is a peptide bond?

Answer 4

Bond between NH2 of one a.a. & COOH of other a.a. ➡ R-(O=)C-N(-H)-R

Question 5

4 Steps of peptide synthesis?

Answer 5

1) protect NH2 of N-terminal a.a. w/ (BOC)2O/Et3N
2) protect COOH of C-terminal a.a. w/ C6H5CH2OH/H2SO4
3) form amide bond w/DCC
4) remove both PGs w/
HBr/CH3CO2H; remove COOH PG w/ H2/Pd-C ➡ continue synthesis