Antipodes (enantiomers) of optically active compounds have different physiological properties e.g. t — Organic Chemistry Chemistry Question
Optical purity
Antipodes (enantiomers) of optically active compounds have different physiological properties e.g. the R-enantiomer of asparagines tastes sweet, whereas the S-enantiomer is bitter. In modern drug design utmost attention is paid to the optical purity of active ingredients. Phenylalanine is an amino acid that is a building block for pharmaceuticals. Enantiomers do not show different signals in the NMR-analysis. However, when suitable derivatives are made, different NMR signals may be possible. For this purpose, phenylalanine methyl ester A which has an optical purity of 75 %, is treated with optically pure Mosher’s reagent P and optically pure reagent Q derived from mandelic acid in the presence of triethylamine, (C2H5)3N.
Draw the formulas of the derivatives which are obtained from compound A with reagent P and reagent Q.
What is the function of triethylamine in this derivatization reaction? Mark the correct answer.
To prevent racemization nof ester A.
To neutralize the hydrogen chloride formed.
The activate ester A.
To form a complex with excess reagent P or Q.
Model Answer
Option 2 (To neutralize the hydrogen chloride formed.)
Sketch the 1H-NMR signals for the following protons in the derivatives made in 11.1. (Note: Compound A has an optical purity of 75 %.)
(a) The methoxy protons of the derivative from P.
(b) The methoxy protons of the derivative from Q.
Sketch the 19F-NMR signal(s) for the derivative from P.