Biologically Active 1-Arylpiperazines. Synthesis of New N-(4-Aryl-1-piperazinyl)alkyl Derivatives of Quinazolidin-4(3H)-one, 2,3-Dihydrophthalazine-1,4-dione and 1,2-Dihydropyridazine-3,6-dione as Potential Serotonin Receptor Ligands

Efficient synthesis of piperazinyl amides of 18β-glycyrrhetinic acid

In the present study, a practical method to prepare piperazinyl amides of 18β-glycyrrhetinic acid was developed. Two main procedures for the construction of important intermediate 8 are discussed. One procedure involves the amidation of 1-Boc-piperazine with 3-acetyl-18β-glycyrrhetinic acid, prepared by the reaction of 18β-glycyrrhetinic acid with acetic anhydride without any solvent at 130 °C. The other procedure to prepare compound 8 involves the amidation of 18β-glycyrrhetinic acid followed by the esterification with acetic anhydride. Finally, compound 8 underwent N-Boc deprotection to prepare product 4. To ascertain the scope of the reaction, another C-3 ester derivative 17 was tested under the optimized reaction conditions. Furthermore, the reasons for the appearance of byproducts were elucidated. Crystallographic data of a selected piperazinyl amide is reported.

Pd-Catalyzed C–H aziridination of 3,3,5,5-tetrasubstituted piperazin-2-ones

Pd-Catalysed C–H aziridination of 3,3,5,5-tetrasubsituted piperazin-2-ones catalysed by succinic acid. The mechanistic role of the acid is investigated through kinetics experiments.

New N- and O-arylpiperazinylalkyl pyrimidines and 2-methylquinazolines derivatives as 5-HT7 and 5-HT1A receptor ligands: Synthesis, structure-activity relationships, and molecular modeling studies

Based on our earlier studies of structure activity relationships on 4-substituted piperazine derivatives, in this work we synthesized a novel set of long-chain arylpiperazines with the purpose of elucidating if some structural modifications in the terminal fragment could affect the binding affinity for the 5-HT₇ and 5-HT_1A receptors. In this new series, the quinazolinone system of the previous derivatives was replaced by a 6-phenylpyrimidine or a 2-methylquinazoline, which were used as versatile building blocks for the preparation of new compounds. A 4-arylpiperazine moiety through a five methylene chain was anchored at the nitrogen or oxygen atom of the heterocyclic scaffolds. The substituents borne by the piperazine nucleus were phenyl, phenylmethyl, 3- or 4-chlorophenyl, and 2-ethoxyphenyl. Binding tests, performed on human cloned 5-HT₇ and 5-HT_1A receptors, showed that, among the newly synthesized derivatives, 4-[5-[4-(2-ethoxyphenyl)-1-piperazinyl]pentoxy]-6-phenyl-pyrimidine (13) and 3-[5-[4-(2-ethoxyphenyl)-1-piperazinyl]pentyl]-2-methyl-4(3H)-quinazolinone (20) displayed the best affinity values, K_i=23.5 and 8.42nM for 5-HT₇ and 6.96 and 2.99nM for 5-HT_1A receptors, respectively. Moreover, the functional properties for both compounds were further evaluated using the cAMP assay. Finally, a molecular modeling study has been performed for 5-HT₇ and 5-HT_1A receptor homology models to investigate the binding mode of N- and O-alkylated pyrimidinones/pyrimidines 4-13, 2-methylquinazolinones/quinazolines 17-22, and previously reported 2- and 3-substituted quinazolinones 23-30.

The Use of 3,6-Pyridazinediones in Organic Synthesis and Chemical Biology

This article gives an overview of the use of 3,6-pyridazinediones in organic synthesis and chemical biology with an emphasis on recent developments. The properties of pyridazinediones, how they are constructed and how they have been applied in various fields of organic synthesis, medicinal chemistry and chemical biology will be highlighted.

Synthesis of Stable Phosphorus Ylides from 6-Chloro-2-Benzoxazolinone and Kinetic Investigation of the Reactions by Uv Spectrophotometry

Stable crystalline phosphorus ylides were obtained in excellent yields from the 1:1:1 addition reactions between triphenylphosphine and dialkyl acetylenedicarboxylates, in the presence of an NH-acid, such as 6-chlorobenzoxazolinone. These stable ylides exist in solution as a mixture of two geometrical isomers as a result of restricted rotation around the carbon-carbon partial double bond resulting from conjugation of the ylide moiety with the adjacent carbonyl group. To determine the kinetic parameters of the reactions, they were monitored by UV spectrophotometry. The second order fits were drawn and the values of the second order rate constant ( k2) were calculated automatically using standard equations within the program. Over the temperature range studied, the dependence of the second order rate constant (Ln k2) on reciprocal temperature was in a good agreement with the Arrhenius equation, leading to the activation energies of all reactions. Furthermore, useful information was obtained from studies of the effect of solvent, the structure of reactants (different alkyl groups within the dialkyl acetylenedicarboxylates) and also the concentration of reactants on the rate of reactions. The proposed mechanism is consistent with the results obtained and the steady state approximation, and the first step ( k2) of reaction was recognized as the rate-determining step on the basis of experimental data.

Synthesis and pharmacological evaluation of new arylpiperazines. 3-[4-[4-(3-chlorophenyl)-1-piperazinyl]butyl]-quinazolidin-4-one - a dual serotonin 5-HT(1A)/5-HT(2A) receptor ligand with an anxiolytic-like activity

On the basis of systematic studies on the structure-activity relationships in arylpiperazine group of serotonin ligands, 12 new derivatives containing quinazolidin-4(3H)-one (1-4), 2-phenyl-2,3-dihydrophthalazine-1,4-dione (5-8) or 1-phenyl-1,2-dihydropyridazine-3,6-dione (9-12) fragments were synthesized. The majority of the tested compounds (2, 4, 7, 8 and 10-12) showed a high affinity for 5-HT(1A) receptors (K(i)=11-54 nM) and two (1, 2) were found active at 5-HT(2A) sites (16 and 68 nM, respectively). All the new 5-HT(1A) ligands tested in vivo revealed an antagonistic activity at postsynaptic 5-HT(1A) receptors, and three of them behaved as agonists at presynaptic ones. Additionally, both the meta-chlorophenylpiperazine derivatives containing quinazolidin-4-one fragment showed features of 5-HT(2A) receptor antagonists. The dual 5-HT(1A)/5-HT(2A) receptor ligand (2) was further tested for its potential psychotropic activity. It showed a distinct anxiolytic-like activity in a conflict drinking test in rats and the observed effect was more potent in terms of the active dose, than that produced by diazepam (used as a reference drug).