RI_H3_PHARM_CHEM_QP_WITH_ANS

3 RAFFLES INSTITUTION 2011 YEAR 6 PRELIMINARY EXAMINATION Higher 3 PHARMACEUTICAL CHEMISTRY 9812/01 Paper 1 20 September 2 hours 30 minutes Additional Materials: Answer Paper Data Booklet READ THESE INSTRUCTIONS FIRST Write your index number, civics tutorial group and name on the Cover Page. Write in dark blue or black pen on both sides of the writing paper. You may use a soft pencil for any diagrams or graphs. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer any five questions. Begin each question on a fresh sheet of paper. At the end of the examination, fasten all your work securely together, with the cover page on top. 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 21 printed pages.

2 © Raffles Institution 2011 9812/01 [Turn Over 1 Analgesics are a group of drugs which are capable of relieving pain. Analgesic drugs act in various ways on the peripheral and central nervous systems. They are distinct from anaesthetics, which reversibly eliminate sensation. One class of analgesic drugs are the non-steroidal anti-inflammatory drugs (NSAIDs). As analgesics, NSAIDs are unusual in that they are non-narcotic . These drugs display analgesic and antipyretic (fe ver-reducing) effects and, in higher doses, have anti-inflammator y effects. The most prominent members of this group of drugs are aspirin and ibuprofen. (a) Outline the differences in the ways in which narcot ic and non-narcotic analgesics work in preventing pain. [2] Aspirin has analgesic property and is capable of an ti-inflammatory and anti-coagulant activities. (b) Briefly explain how aspirin acts as an anti-inflammatory. [2] Aspirin acts as an acylating agent to bring about c ovalent bond (ester) formation at the serine binding site in the enzyme receptor, as shown below. (c) Show the mechanism of the transesterification reaction. [3] Ibuprofen, another NSAID, is also analgesic and has anti-inflammatory properties. ibuprofen 2-(4-(2-methylpropyl)phenyl)propanoic acid Ibuprofen is produced industrially as a racemate. T he compound contains a chiral centre in the α-position of the propionate moiety. As such, there are two possible enantiomers of ibuprofen, (S)- and ( R)-ibuprofen, each with the potential for different biological effects and metabolism from the other. When a racemic mixture o f ibuprofen is esterified with butan-2-ol, four possible diastereomers can be obtained. (d) Draw the structures of ( S)-ibuprofen and the diaste