Dopamine agonists: structure-activity relationships

Design, synthesis and anticholinergic properties of novel α-benzyl dopamine, tyramine, and phenethylamine derivatives

Due to the important biological properties of dopamine, phenethylamine, and tyramine derivatives in the central nervous system, herein the synthesis of novel α-benzyl dopamine, phenethylamine, and tyramine derivatives is described. The title compounds were synthesized starting from 3-phenylpropanoic acids and methoxybenzenes in six or seven steps. Firstly, 3-(2,3-dimethoxyphenyl)propanoic acid (11) and 3-(3,4-dimethoxyphenyl)propanoic acid (12) were selectively brominated with N-bromosuccinimide (NBS). The Friedel-Crafts acylation of methoxylated benzenes with these brominated acids or commercially available 3-phenylpropanoic acid in polyphosphoric acid gave the desired dihydrochalcones. α-Carboxylation of dihydrochalcones, reduction of benzylic carbonyl groups, hydrolysis of esters to acid derivatives, and the Curtius rearrangement reaction of acids followed by in situ synthesis of carbamates from alkyl isocyanates and hydrogenolysis of the carbamates afforded the title compounds in good total yields. Alzheimer's disease (AD) and Parkinson's disease (PD) are chronic neurodegenerative diseases that become serious over time. However, the exact pathophysiology of both diseases has not been revealed yet. There have been many different approaches to the treatment of patients for many years, especially studies on the cholinergic system cover a wide area. Within the scope of this study, the inhibition effects of dopamine-derived carbamates and amine salts on the cholinergic enzymes AChE and BChE were examined. Dopamine-derived carbamate 24a-i showed inhibition in the micro-nanomolar range; compound 24d showed a Ki value of 26.79 nM against AChE and 3.33 nM against BChE, while another molecule, 24i, showed a Ki range of 27.24 nM and 0.92 nM against AChE and BChE, respectively. AChE and BChE were effectively inhibited by dopamine-derived amine salts 25j-s, with Ki values in the range of 17.70 to 468.57 µM and 0.76-211.23 µM, respectively. Additionally, 24c, 24e and 25m were determined to be 60, 276 and 90 times more selective against BChE than AChE, respectively.

Serotonergic and dopaminergic activities of rigidified (R)-aporphine derivatives

Novel rigidified (R)-aporphine derivatives were synthesized from (R)-1,11-carbonylaporphine by ring expansion reactions. The structures of the novel analogues were assigned by NMR spectroscopy and X-ray crystallography. The compounds showed moderate affinities and selectivities at serotonin S-HT1A and 5-HT7 and dopamine D2A receptors.

Enantioselective synthesis of rigid 2-aminotetralins. Utility of silicon as an oxygen and nitrogen surrogate in the tandem addition reaction

Dimethylphenylsilyllithium undergoes a highly diastereoselective conjugate addition to chiral naphthyloxazoline 11. Electrophilic trapping of the resulting aza-enolate affords the tandem addition product (12) in high yields as a single diastereomer. The silicon, thus incorporated, may be protodesilylated and undergoes a Tamao oxidation to afford the corresponding alcohol. By chemical modification of the oxazoline, both the gamma-lactone (28) and the delta-lactone (37) were prepared. Reduction of each lactone followed by oxidation of the ensuing diol gave the keto aldehyde. Double reductive amination of the 1,4-dicarbonyl (from the gamma-lactone) allowed the synthesis of two novel hexahydrobenz[e]indoles, 20 and 35. Double reductive amination of the 1,5-dicarbonyl (from the delta-lactone) gave access to two novel octahydrobenzo[f]quinolines, 41 and 43. An unprecedented rearrangement of nitro alcohol 26 into lactone 28 is described and a reasonable mechanism for its formation postulated.

Synthesis, resolution, and preliminary evaluation of trans-2-amino-6(5)-hydroxy-1-phenyl-2,3-dihydro-1H-indenes and related derivatives as dopamine receptors ligands

The present work reports the synthesis of enantiomeric pairs of the trans-2-amino-6-hydroxy-1-phenyl-2,3-dihydro-1H-indene [(+)-14a, (-)-14a] and trans-2-amino-5-hydroxy-1-phenyl-2,3-dihydro-1 H-indene [(+)-14b, (-)-14b] and their N,N-di-n-propyl [(+)-and (-)-15a,b], N-methyl-N-allyl [(+)-and (-)-16a,b], and N-methyl-N-n-propyl [(+) and (-)-17a,b] derivatives obtained by a combination of stereospecific reactions and optical resolution. The new compounds were evaluated for their affinity at the dopamine D1 and D2 receptors. The amines (+)- and (-)-14a, incorporating the D1 pharmacophore 2-phenyl-2-(3-hydroxyphenyl)ethylamine in a trans extended conformation, and their derivatives displayed D1 and D2 affinity in the nanomolar range. On the other hand, the enantiomers (+)- and (-)-14b, (+)- and (-)-15b displayed high affinity and selectivity for the D1 receptor. In a preliminary behavioral study on rats (+)-14b, and to a greater extent (+)-15b, promoted episodes of intense grooming, thus indicating that they act as central D1 agonists. The trans-2-amino-5-hydroxy-1-phenyl-2,3-dihydro-1H-indenes (+)-14b and (+)-15b represent selective D1 agonists lacking a catechol group, which should meet the prerequisites for a central nervous system penetration.

Information processing in mammalian olfactory system

In recent years, considerable progress has been made in understanding how the olfactory system uses neural space to encode sensory information. In this review, we focus on recent studies aimed at understanding the organizational strategies used by the mammalian olfactory system to encode information. The odorant receptor gene family is discussed in the context of its genomic organization as well as the specificity of olfactory sensory neurons. These data have important consequences for the mechanisms of odorant receptor gene choice by a given sensory neuron. Division of the olfactory epithelium into zones that express different sets of odorant receptors is the first level of input organization. The topographical relationship between periphery and olfactory bulb represents a further level of processing of information and results in the formation of a highly organized spatial map of information in the olfactory bulb. There, local circuitry refines the sensory input through various lateral interactions. Finally, the factors that may drive the development of such a spatial map are discussed. The onset of expression and the establishment of the zonal organization of odorant receptor genes in the epithelium are not dependent upon the presence of the olfactory bulb, suggesting that the functional identity of olfactory sensory neurons is determined independently of target selection.

Some analogues of 1,4-disubstituted piperazines as hypnotic and sedative agents

Preparation, analytical data, and biological properties such as acute toxicity, influence on spontaneous and amphetamine induced locomotor activity, hypnotic activity, influence on hexobarbital narcosis and anticonvulsant activity of new analogues of pyrimidyl piperazines--ethyl 3-[4-(2-pyrimidyl)-1-piperazinyl]-3-oxopropanoate (4), 1-[4-(2-pyrimidyl)-1-piperazinyl]-1,3-butandione (5), ethyl 3-[4-(2-pyrimidyl)-1-piperazinyl]butanoate (6) and 1-[4-(2-pyrimidyl)-1-piperazinyl]-2-acetyl-1-hexanone (7)--are reported.

ALADDIN: an integrated tool for computer-assisted molecular design and pharmacophore recognition from geometric, steric, and substructure searching of three-dimensional molecular structures

ALADDIN is a computer program for the design or recognition of compounds that meet geometric, steric, and substructural criteria. ALADDIN searches a database of three-dimensional structures, marks atoms that meet substructural criteria, evaluates geometric criteria, and prepares a number of files that are input for molecular modification and coordinate generation as well as for molecular graphics. Properties calculated from the three-dimensional structure are described by either properties calculated from the molecule itself or from the molecule as compared to a reference molecule and associated surfaces. ALADDIN was used to design analogues to probe a bioactive conformation of a small molecule and a peptide, to test alternative superposition rules for receptor mapping of the D2 dopamine receptor, to recognize unexpected D2 dopamine agonist activity of existing compounds, and to design compounds to fit a binding site on a protein of known structure. We have found that series designed by ALADDIN show much more subtle variation in shape than do those designed by traditional methods and that compounds can be designed to be very close matches to the objective.

Dopamine receptors: classification, properties and drug development

1. The pharmacology, biochemistry and structure-activity relationships pertinent to the D1 and D2 subtypes of dopamine receptors are reviewed. 2. Recent advances in receptor purification and our understanding of the secondary messenger systems involved are presented. 3. D1 and D2 receptors of central nervous, endocrine and peripheral systems are identical.

A three dimensional receptor model of the dopamine D2 receptor from computer graphic analyses of D2 agonists

Four potent D2 agonists were employed to define a primary pharmacophore for the D2 receptor. Hypothetical receptor points, representing interaction points on a receptor were built on to each molecule. These points and the nitrogen atom were averaged to give the coordinates (A) of the primary pharmacophore: R1 (0.00, 3.50, 0.00), R2 (0.00, -3.50, 0.00), R3 (5.79, 2.06, 0.00), and nitrogen (5.13, -0.63, 0.37). Eight structural classes of D2 agonists were then superimposed on to the primary pharmacophore to aid in the location of secondary binding sites. The secondary sites include two lipophilic clefts, an area of steric bulk, a region to hydrogen bond 'meta' hydroxy groups and a 'critical region' accepting methoxy and halogen substituents but not hydroxy substituents. The model has the potential to design and predict activity of novel D2 agonist compounds.

The D-1 dopamine receptor

The D-1 receptor will provide a fruitful ground for many scientists in the coming years. Pure biochemists will attempt to isolate, purify and sequence the molecule itself. Functional biochemists will study the mechanisms whereby the receptor regulates adenylate cyclase activity. Physiologists will attempt to study the consequences of stimulating the receptor in either the brain or in peripheral tissues. Animal behavioralists will attempt to understand how the receptor participates in the generation of animals response to dopaminergic drugs (both agonists and antagonists). Finally, it remains to be determined if any novel therapeutic agents targeted towards the D-1 receptor will become commercially viable compounds.

Crystallographic, theoretical and molecular modelling studies on the conformations of the salicylamide, raclopride, a selective dopamine-D2 antagonist

The structure of the potent dopamine-D2 antagonist, raclopride, (S)-3,5-dichloro-N-[(1-ethyl-2-pyrrolidinyl)methyl]-6-methoxysalicylamid e (+)-tartrate, has been determined by X-ray crystallography. The benzamide moiety of raclopride is planar in accordance with other salicylamides (FLA 797 and eticlopride). The planar conformation is stabilized by two intramolecular hydrogen bonds, i.e. one between the amide hydrogen and the methoxy group and one between the phenol hydrogen and the carbonyl group. The side-chain of raclopride has an extended conformation in contrast to the solid state conformations of FLA 797 and eticlopride. The side-chain conformations were studied by rigid rotations followed by MM2PI relaxations of the eight local minima found. Small energy differences (less than 4.0 kcal mol-1) exist between the various extended and folded conformations. Based on modelling studies with piquindone as template, it is suggested that the salicylamides with N-ethyl-2-pyrrolidinylmethyl side-chains interact with the dopamine-D2 receptor in a folded or a half-folded conformation.