NEUROPSYCHIATRY DSM (PYDI 0416) FALL, 1999 MEDICINAL CHEMISTRY OF ANTIPSYCHOTICS DR. RILEY A. INTRODUCTION

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1 EUPYCIATY DM (PYDI 0416) ALL, 1999 MEDICIAL CEMITY ATIPYCTIC D. ILEY A. ITDUCTI Antipsychotic (neuroleptic) agents are primarily used in the therapy of schizophrenia, organic psychoses, the manic phase of manic-depressive illness and other acute or chronic idiopathic psychotic illnesses. B. MECAIM ACTI Evidence supports the hypothesis that the etiology of psychotic disorders lies in neurochemical defects of dopaminergic and serotonergic pathways in the brain. This hypothesis is supported by the fact that the primary pharmacological action of antipschotic agents is antagonism of dopamine and/or serotonin receptor in the C. A development-based classification of antipsychotic drugs: rder of binding affinity for C T receptors Classical Antipsychotics (phenothiazines) D 2. D 1 > " 1. 5T 2 Atypical (DA) Antipsychotics irst-generation (butyrophenones) D 2 > D 1. 5T 2 > " 1 econd-generation (risperidone, clozapine) D 2. 5T 2 >> D 1 > " 1 1

2 Dopamine Biosynthesis and Catabolism 2 Tyrosine hydroxylase 2 L-Tyrosine C 2, e 2+, A 4 (rate limiting) C L-Dihydroxyphenylalanine (L-DPA) Pyridoxal phosphate L-Aromatic amino acid decarboxylase (L-AAAD) C MA 2 Dopamine β-hydroxylase 2 3,4-Dihydromandelic acid Aldehyde oxidase Dopamine -orepinephrine Catechol -methyl transferase AM Catechol -methyl transferase C 3 C MA C 3 2 Aldehyde oxidase 2

3 erotonin Biosynthesis and Catabolism 2 C L-Tryptophan Tryptophan hydroxylase (rate limiting) 5 2 C L-5-ydroxytryptophan Aromatic Amino Acid Decarboxylase C MA 2 5-ydroxyindoleacetaldehyde (5-IA) 5-ydroxytryptamine (5-T, serotonin) Aldehyde oxidase C 5-ydroxyindoleacetic Acid (5-IAA) 3

4 C. ATIPYCTIC DUG CLAE PETIAZIE DEIVATIVE The first-used class of efficacious antipsychotic agents Chlorpromazine, the prototypical member of this class, was first used to treat mental disease in onselective DA-receptor antagonists; also act at other neurotransmitter receptors giving rise to significiant A profiles 9 Phenothiazine 1. tructural Properties 10 2 heterocycle phenothiazine or bioisosteric heterocycle a connector alkyl (side) chain terminated by an aliphatic 3E-amine function 2. Physicochemical Properties Alkyl connector 2 o 3 -amine the phenothiazine heterocycle confers a high degree of lipophilicity on these antipsychotics which is balanced (solubility) by the cationized (at physiologic p) amine function the phenothiazines possess two potentially basic functional groups: < the 10 -amine which is very weakly basic (pk b >10) because of the electronwithdrawing effects of the 2 benzene rings attached to it and is not appreciably cationized at phys. p, < the side chain tertiary amine function which confers strong organic basicity on the antipsychotic phenothiazines solubility of the AP phenothiazines is increased for oral dosage formulation by treatment with an acid: Cl Cl - 4

5 conversely, the 2 soly of these drugs can be reduced through the formation of bioreversible hydrocarbon esters (prodrugs) thereby lowering dissolution rates and facilitating formulation of long-acting (1%3 weeks) depot injections: C 3 Prodrug Design Bioactivation C 3 C(C 2 ) n C 3 luphenazine (tid and qid) luphenazine enanthate: n = 5 (1-2 wks.) luphenazine decanoate: n = 8 (2-3 wks) 3. tructure-activity elationships structural/steric complementarity has been demonstrated between the phenothiazines and the C neurotransmitter dopamine providing an explanation for the ability of the antipsychotic molecules to interact in an antagonistic fashion with DA receptors: A = B = C = D = phenothiazine antipsychotic dopamine superposition of phenothiazine and dopamine structures (note complementarity of Ar rings and basic amine functions) superposition of phenothiazine (with alkylamine side chain oriented in opposite direction) not lack of complementarity of basic amine functions 5

6 structural modification of the phenothiazines: (1) thioxanthene bioisosteres - derived by replacing the -C 2 structural feature of the phenothiazines with a bioisosteric double bond: 2 Phenothiazine Bioisosteres 2 Thioxanthene (cis > trans) (2) addition of an electronegative atoms/group at C2 of the phenothiazine ring enhances antipsychotic potency, e.g.: = 2 2 > C 3 > CC 3 > Cl (3) a 3-carbon alkyl connector between phenothiazine heterocycle and terminal 3E-amine function is optimal for dopamine-receptor blockade and antipsychotic activity. hortening of the chain to 2-carbons results in a change in receptor affinity from DA to C histamine receptors. 2 2 Antidopaminergic Antihistaminic 6

7 (4) tructural modification of the side chain amine function yields three AP phenothiazine subclasses: 2 Aliphatic phenotiazine derivatives Piperidine phenotiazine derivatives Piperazine phenotiazine derivatives (5) pharmacologic/therapeutic profiles of these 3 classes of antipsychotics differ as follows: Antipsychotic potency: piperazines > piperidines > aliphatics EP frequency: piperazines > piperidines > aliphatics edation: aliphatics. piperidines > piperazines ypotension: aliphatics > piperidines > piperazines 4. Biotransformation of the Antipsychotic Phenothiazines as depicted, several different biotransformation reactions occur for the same phenothiazine molecule, numerous metabolites are formed and excreted, the 7- metabolite is an active antidopaminergic while the sulfoxide (=) metabolite is inactive note than the thioxanthene derivatives do not form aromatic hydroxylated metabolites metabolic pathways are significantly altered by a variety of factors (age, sex, interaction with other drugs, route of administration, etc.) [] 7 [] D 7

8 4. Therapeutic Phenothiazines Aliphatic and Piperidine Phenothiazines ame = = Chlorpromazine (C 2 ) 3 (C 3 ) 2 Cl Triflupromazine (C 2 ) 3 (C 3 ) 2 C 3 Promazine (antiemetic) (C 2 ) 3 (C 3 ) 2 Thioridazine Mesoridazine (C 2 ) 2 C 3 C 3 C3 Piperactazine Perphenazine (C 2 ) 2 CC 3 Cl C 2 C 2 C 2 Piperazine Phenothiazines ame = = Prochlorperazine C 3 Cl luphenazine (C 2 ) 2 C 3 Trifluoperazine C 3 C 3 Acetophenazine (C 2 ) 2 CC 3 Thiethylperazine (C 2 ) 2 C 2 C 3 8

9 ETECYCLIC AALGUE TE PETIAZIE tructural Class Thioxanthenes < olefin bioisosteres of the phenothiazines < e.g. Thiothixene tructure 2 2 C 3 Arylbutylpiperidines < potent D2 receptor antagonists < two structural variants: 1) luorobutyrophenone (aloperidol) 2) Diarylbutylpiperidine (Pimozide) aloperidol and Decanoate Prodrug Decanoate ester Cl Pimozide Dihydroindolones < Molindone ydrochloride Cl - C C 3 9

10 tructural Class tructure Dibenzazepines < four structural variants 1) Dibenzoxazepine (=) (Loxapine) 2) Dibenzodiazepine (=) (Clozapine) 3) Dibenzothiazepine (=) (Quetiapine) 4) Thienobenzodiazepine (=) 8 3 C + 4' - C 11 2 Loxapine succinate Cl C Cl 8 Clozapine 4' C 3 2 C 2 C 2 C 2 C C C C 3 4' Quetiapine fumarate lanzapine C 3 Benzisoxazoles < isperidone + Cl- C 3 10

11 AYLBUTYLPIPEIDIE tructural Variants: Phenone 2 piperidine butyl p-fluoro 4C = butyro lurobutyrophenone 3 o -amine Ar Ar diaryl Diarylbutylpiperidine Physicochemical Properties < lipophilic < basic (3E-amine) - forms 2 -soluble salts tructure-activity elationships < para- or similar electronegative substituent (e.g. C 3 ) provides maximal potency, < lengthening, shortening or branching of the butyro (4 carbon) chain decreases neuroleptic potency, < terminal basic amine function may vary in structure but is usually incorporated in a 6- membered heterocyclic ring < replacement of the C= function with a C-Ar structural feature yields therapeuticallyuseful antipsychotics (e.g. pimozide) Metabolism [] D 11

12 DIBEZAZEPIE A class of neuroleptics that utilizes the tricyclic dibenzazepine heterocycle as a basic structural feature, The dibenzazepine heterocycle is a lipophilic structure with very weakly basic properties, tructural variants of dibenzazepines: < Dibenzoxazepine ( = ) < Dibenzodiazepine ( = ) < Dibenzothiazepine (=) < Piperazine substitution at C-11 providing a center ( 4' ) of basicity for 2 -solubilizing salt formation to facilitate oral dosage formulation Aromatic (imine) Dibenzazepine heterocycle Piperazine 11 thiophene bioisostere may be,, = : dibenzdiazepine = : dibenzoxazepine = : dibenzothiazepine atypical antipsychotics: clozapine quetiapine olanzapine 12

13 IPEIDE a benzisoxazole derivative with high affinity for central serotonergic 5-T 2, dopaminergic D 2 (DA ratio. 5) and adrenergic " 1 -receptors in vivo has improved efficacy vs. both positive (delusions and hallucinations) and negative (diminished emotions, low motivation) symptoms of schizophrenia and reduced EP Cl salt used for oral formulation + Cl - C 3 Metabolism (1) Alicyclic hydroxyation ([]) the 9- metabolite is a potent atypical antipsychotic (2) xidative -dealkylation (D) (3) Benzisoxazole ring cleavage ring scission D C [] [] 13