Cl or C here H 2 N. 4. Consider the following local anesthetic agents and find the pharmacophore. Double bonds. have been omitted for clarity.

Transcription

1 Lecture 15 omework Key Medicinal Chemistry 1. Associate each one of the following terms with one of the three phases: pharmaceutical (PC), pharmacokinetic (PK), pharmacodynamics (PD) PC refers to getting the drug into the patient; PK refers to getting the drug where it needs to go in the body, considering ADME (adsorption, distribution, metabolism, and elimination) (a) Absorption - PK (b) dosage form - PC (c) receptor - PD (d) metabolism - PK (e) binding site - PD (f) elimination - PK (g) excipient (inactive ingredients like solvent) - PC (h) oral administration - PC 2. Classify each method of drug administration as enteral (E) or parenteral (P): (a) Inhalation - P (b) ubcutaneous - P (c) Rectal - E (d) Intravenous - P (e) ral - E (f) Topical - P (g) Intramuscular - P (h) ublingual - P 3. Consider the following local anesthetic agents and find the pharmacophore. Double bonds have been omitted for clarity. 4. Consider the following local anesthetic agents and find the pharmacophore. Double bonds have been omitted for clarity. Cl or C here X 2

2 Lecture 16 W Key 5. Calculate the therapeutic index of a drug that produces a toxic effect in 50% of the test population at a dose of 85 mg/kg and has a therapeutic effect in 50% of the test population at a dose of 100 µg/kg. Is this a better drug than a similar one with a therapeutic index of 100? Justify your answer. 100 µg/kg = 0.1 mg/kg. TI is unitless, provided the units in the numerator and denominator are the same. TI = ToxicEffect 50 = 85mg/kg TherapeuticEffect mg/kg = 850 This is a better drug than another with a TI of 100. The greater the TI, the larger the margin of safety. 6. Consider the structures of the following drugs and predict if they are soluble in water. If not, what would you do to increase its solubility? Does p affect the solubility potential? (a) Ropivacaine (see #3) : 2-3 C amine: 3C olubility Potential + 3 C (amine) 5-6 C Ropivacaine Ropivacaine has a total of 17 carbon atoms. The solubility potential of 5-6 carbon atoms is smaller than the total number of carbons, thus the molecule is expected to be insoluble in water. To increase its solubility we should ionize the molecule. The only group that is easily ionizable is the amine which can be protonated with Cl or 2 4. Cl Cl Ropivacaine Ropivacaine hydrochloride By adding an ionic group the solubility potential increases sharply to a total of carbons: olubility Potential C C (ammonium salt) The solubility potential is now larger than the total number of carbons and the molecule is expected to be soluble in water.

3 (b) Mephobarbital carbonyl urea carbonyl Mephobarbital The heterocyclic ring of Mephobarbital is not listed in Table 1 as such and, thus, it must be divided into smaller groups for the purpose of the calculation. ne way of dividing it (but not the only way) would be to consider the urea group (urea: 2 -C- 2 ) and two carbonyl groups next to the urea. Technically, these carbonyls belong to larger imide groups (-C--C-) but since we are considering them as separate entities, just for the purpose of the calculation we can equate them to ketones or aldehydes. olubility Potential 6 C 2 C (urea) 2 C (carbonyl: ald. or ket.) + 2 C (carbonyl: ald. or ket.) Another way of dividing the molecule into smaller groups is to consider two groups and a carbonyl: carbonyl Mephobarbital With this approach the solubility potential is slightly different: 6-8C. + 2 C (carbonyl: ald. or ket.) olubility Potential 6-8 C Mephobarbital has a total of 13 C. ince the solubility potential is smaller than the total number of carbons, the molecule is expected to be insoluble in water. To increase its

4 solubility, a sodium salt could be made. In the presence of a the tautomeric equilibrium is shifted to the enol form. The hydrogen is acidic and is pulled by the base forming a sodium salt. a Mephobarbital tautomer acidic a a charged olubility Potential C (charged ) By ionizing the molecule, its solubility potential increases to C and, thus, the compound is expected to be soluble in water.

5 (c) Indomethacin At acidic p, the carboxylic acid is protonated. ether 3 C C carboxylic acid Cl olubility Potential 7-8 C 3 C (carboxylic acid) + 2 C (ether) The compound is expected to be insoluble in water. Its solubility potential (7-8 C) is smaller than the total number of carbons (19 C). At a p higher than the pk a of the carboxylic acid (pk a 5-6), Indomethacin is mainly in the ionized form. The solubility potential increases to C and the compound is expected to be soluble. carboxylate 3 C C - Cl C (carboxylate) + 2 C (ether) olubility Potential C

6 7. The pka s of Butorphanol, a potent analgesic in the morphine family, are 7.97 and (a) Keeping in mind that the structure provided is at physiological p, identify the acidic protons and indicate which pka goes with which proton. (b) What is the charge of butorphanol at p 2? p 5? p 11? 3 o amine pk a1 (B + ) = 7.97 alcohol (neutral) phenol pk a2 = At p 2 and 5 and 7 (p < pk a1 ; p < pk a2 ) both groups will be protonated: At p 11 (p > pk a1 ; p > pk a2 ) both groups will be mainly deprotonated.

7 8. Propose a structure for the active metabolite of Famciclovir, an antiviral agent. In other words, which bonds are likely to be metabolized and what would be the resultant structure? The esters are likely hydrolyzed C 3 C Famciclovir active compound 9. Calculate the solubility potential of Penicillin G and Isopenicillin using the solubility potential table from lecture s (4-6 C's) Penicillin G thioether (2 C's) C 2 - carboxylate (20-30 C's) olubility Potential = 26 to 38 C's Greater than number of C's in Penicillin G (16) Water-soluble - 2 C carboxylates and 1 ammonium (60-90 C's) 2 s (4-6 C's) thioether (2 C's) Isopenicillin C 2 - olubility Potential = 66 to 98 C's Greater than number of C's in Isopenicillin (14) Water-soluble fo sho!