NYJC_H3_Chemistry_P1_Answers

[Turn over NANYANG JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION Higher 3 PHARMACEUTICAL CHEMISTRY 9812/01 Paper 1 29 September 2014 2 hours 30 minutes Additional Materials: Answer Paper Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer any five questions. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. You may use a calculator. You are reminded of the need for clear presentation in your answers. This document consists of 17 printed pages and 1 blank page. ANSWERS

2 H3 Chemistry 9812/01 NYJC J2/14 PX [Turn over 1(a) Propranolol was the first successful beta blocker developed to treat hypertension. It was developed by the British scientist James W. Black in the 1960s. In 1988, he was awarded the Nobel Prize in Medicine for this discovery. Propranolol acts as an antagonist to the -adrenergic receptors in the smooth muscle tissues of the heart. propranolol (i) Describe what is meant by the terms agonist and antagonist. [2] Answers: An agonist is a drug which mimics the natural ligand for a receptor.  An antagonist is a drug which docks well to the binding site, but does not cause the required change of shape of the receptor.  Propranol is sold as a racemate, a mixture of two isomers. The (R) -enantiomer is the beta-blocker for the heart and the (S)-enantiomer is a contraceptive. (ii) Suggest why propranolol is sold as a racemate , even though only one of its enantiomers is useful for treating hypertension. [1] Answers: The other enantiomer is not hazardous for the body and it is cheaper to produce the racemate. Unless the person taking the drug is a woman who wants to get pregnant, the racemate should not cause any problems.  (iii) Draw the two optical isomers of propranolol. [2] Answers: OH HO O C C O CH2 CH2NHCH(CH3)2 (CH3)2CHNHCH2 CH2 H H  