PHYSICOCHEMICAL PROPERTIES OF DRUG ACTION

Transcription

1 PHYSICCHEMICAL PRPERTIES F DRUG ACTIN III Year B.Pharm I Sem Subject: Medicinal Chemistry-I Presented by: Mr. N. Uday Kumar M.Pharm (Ph.D)

2 PHYSICCHEMICAL PRINCIPLES F DRUG ACTIN

3 INTRDUCTIN Drug molecules interact with biological structures drug effect lipoproteins/enzymes membranes nucleic acids

4 DRUG EFFECT Drug effect is preceded by drug transport from site of application to site of action and is dependent on physicochemical properties

5 PHYSICCHEMICAL Interatomic distances Intermolecular forces Stereochemistry Partition coefficient Solubility Ionization PRPERTIES All affect pharmacokinetics

6 PHARMACKINETICS Tissue Depots ABSRPTIN unbound drug THIS WE MUST Plasma Receptors T UNDERSTAND ALL unbound drug bound drug unbound drug UNDERSTAND bound drug EXCRETIN PHYSICCHEMICAL bound drug PRPERTIES metabolites METABLISM

7 PHYSICCHEMICAL Interatomic distances Intermolecular forces Stereochemistry Partition coefficient Solubility Ionization PRPERTIES

8 PARTITIN CEFFICIENT Hydrophobic bonding interactions are critical Can be approximated by partition coefficient PC Drug (W) Drug () PC = [drug] [drug] W Thus, PC describes the entire drug.

9 PARTITIN CEFFICIENT Useful to know the hydrophobic bonding properties of substituent groups. Hydrophobic bonding constant for a substituent is obtained as a difference In log P. = log P X - log P H P X = PC for substituted compound P H = PC for parent compound Thus, describes the substituent.

10 REPRESENTATIVE VALUES Substituent Aromatic Aliphatic C 6 H n-c 4 H Cl H N CH H

11 SLUBILITY Drugs must be in solution to interact with receptors. Drugs have some degree of solubility in both aqueous and lipid compartments (PC). Solubility is a function of: ionization molecular structure molecular weight stereochemistry electronic structure

12 SLUBILITY of WEAK ELECTRLYTES Solubility will be affected by ph. Acidic drugs Basic drugs Amphoterics barbiturates, NSAIDs phenothiazines, -blockers tetracyclines, ACEIs

13 SLUBILITY of WEAK ELECTRLYTES indomethacin tetracycline Aqueous solubility chlorpromazine ph

14 PREDICTING WATER SLUBILITY Empiric method Analytic method Solubility in water ionic compounds, i.e. salts of WA, WB polar compounds, i.e. those that H-bond

15 EMPIRIC METHD Solubility Properties of Na Salts of Common rganic Acids R C H + MH R C M + H 2 H H R C H H H H Na

16 EMPIRIC METHD Solubility Properties of Na Salts of Common rganic Acids RC - Na + Solubility (g/100g H2) C 6 H CH H 2 solubility can be increased by salt formation CH 3 CH CH 3 (CH 2 )

17 EMPIRIC METHD Solubility Properties of Common rganic Acids RCH CH 3 (CH 2 ) 2 Solubility (g/100g H2) CH 3 (CH 2 ) CH brings into solution 5 6 C s to extent of 1% CH 3 (CH 2 ) CH 3 (CH 2 ) 16 insoluble

18 EMPIRIC METHD Solubility Properties of Common Alcohols RH Solubility 2-propanol (g/100g H2) 1-butanol 7.9 RH brings into solution 5 6 C s to extent of 1% 2-butanol pentanol 2.3

19 EMPIRIC METHD Solubility Properties of Common Amines NR 1 R 2 R 3 R1 R2 R3 Solubility (g/100g H2) Me H H very soluble Me Me Me 91 Et H H very soluble N brings into solution 6 7 C s to extent of 1% Et Et Et 14 Ph H H 3.7 Ph Me Me 1.4

20 EMPIRIC METHD Solubility Properties of Common Phenols ArH Solubility (g/100g H2) cyclohexanol 3.6 phenol 9.3 p-cresol 2.3 ArH brings into solution 6 7 C s to extent of 1% m-chlorophenol 2.6 catechol 45.0

21 BASIS F EMPIRIC METHD For monofunctional compounds a single functional group (capable of H-bonding) will bring into solution 5 7 carbons to the extent of 1%. but Drugs are usually not simply monofunctional. Simple summation of water-solubilizing potential may not give accurate predictions.

22 EMPIRIC METHD solubility defined as 1% Water Solubilizing Potential of Functional Groups Group Mono Poly RH 5-6 C 3-4 C ArH RR RCH R 2 C N(R) RCH RCR 6 3 RRNCR Urea, carbamate, etc 2

23 EMPIRIC METHD H CH H NH 2 CH 2 CHCH NH C 6 7 C 6 7 C tyrosine Prediction: C should be brought into solution. nly 9 C present, so should be >1% soluble. Experimental Results: 0.045% solubility WHY?

24 EMPIRIC METHD CH 2 CHC H NH 3 intramolecular ionic bonding reduces solubility ph adjustment increases solubility Polyfunctional data compensates for intra- and intermolecular bonding. Group Mono Poly RH 5-6 C 3-4 C ArH

25 EMPIRIC METHD CH 3 C 19 H 19 N 4 C 21 H 23 N 5 H CH 3 C N CH 3 CH 3 C NCH 3 Mono = = 24 soluble soluble Poly = = 11 insoluble insoluble

26 ANALYTIC METHD log P = [drug] octanol [drug] water log P is a measure of the solubility of the whole drug is the log P of the fragment solubility defined as >3.3% logp calc = fragments if calc. logp is > +0.5 then compound is H 2 insoluble if calc. logp is < +0.5 then compound is H 2 soluble

27 ANALYTIC METHD Values for rganic Fragments solubility defined as >3.3% Fragment Value C (aliphatic) +0.5 phenyl +2.0 Cl N (nitrate) +0.2 IMHB S 0.0 C, CN -0.7, N N (aliphatic) N (aromatic) -0.28

28 ANALYTIC METHD 1. table is only a brief compilation 2. values are approximations 3. values depend on whether fragment aromatic or aliphatic 4. values are obtained under nonionizing conditions 5. intramolecular H-bonding must be considered 6. values for heterocycles can be estimated

29 ANALYTIC METHD H 2 N C CH 2 CH 2 N Et Et procaine solubility defined as >3.3% phenyl =C insoluble

30 ANALYTIC METHD S N Cl CH 2 CH 2 CH 2 N CH 3 CH 3 chlorpromazine solubility defined as >3.3% Cl S 0.0 Calc Exp. +5.3

31 ANALYTIC METHD H N amobarbital CH 3 CH 2 CH 3 CHCH 2 CH 2 CH 3 N H solubility defined as >3.3% Calc Exp. +2.1

32 ANALYTIC METHD CH 2 C NH N S Me Me CH penicillin V solubility defined as >3.3% CN, S 0.0 Calc Exp. +2.1

33 ANALYTIC METHD CH 2 H CHH CH 2 H glycerol solubility defined as >3.3% Calc Exp. 1.7