Ligand design and synthesis of new imidazo[5,1-b]quinazoline derivatives as α1-adrenoceptor agonists and antagonists

Photochemical and Electrochemical Applications of Proton-Coupled Electron Transfer in Organic Synthesis

We present here a review of the photochemical and electrochemical applications of multi-site proton-coupled electron transfer (MS-PCET) in organic synthesis. MS-PCETs are redox mechanisms in which both an electron and a proton are exchanged together, often in a concerted elementary step. As such, MS-PCET can function as a non-classical mechanism for homolytic bond activation, providing opportunities to generate synthetically useful free radical intermediates directly from a wide variety of common organic functional groups. We present an introduction to MS-PCET and a practitioner's guide to reaction design, with an emphasis on the unique energetic and selectivity features that are characteristic of this reaction class. We then present chapters on oxidative N-H, O-H, S-H, and C-H bond homolysis methods, for the generation of the corresponding neutral radical species. Then, chapters for reductive PCET activations involving carbonyl, imine, other X═Y π-systems, and heteroarenes, where neutral ketyl, α-amino, and heteroarene-derived radicals can be generated. Finally, we present chapters on the applications of MS-PCET in asymmetric catalysis and in materials and device applications. Within each chapter, we subdivide by the functional group undergoing homolysis, and thereafter by the type of transformation being promoted. Methods published prior to the end of December 2020 are presented.

Iodine promoted dual oxidative C(sp3)-H amination of 2-methyl-3-arylquinazolin-4(3H)-ones: a facile route to 1,4-diarylimidazo[1,5-a]quinazolin-5(4H)-ones

An iodine promoted tandem oxidative condensation of benzylamines and 2-methylquinazolin-4-(3H)-ones was developed to yield imidazo[1,5-a]quinazolin-5(4H)-ones via dual C(sp³)-H amination under metal free conditions in a greener way using molecular oxygen as a terminal oxidant. This tandem transformation provides an efficient approach to construct various functionalized imidazo[1,5-a]quinazolin-5(4H)-ones in a straightforward manner via a sequential amination-oxidation-annulation-aromatisation.

n-Bu4NI-catalyzed selective dual amination of sp3 C–H bonds: oxidative domino synthesis of imidazo[1,5-c]quinazolines on a gram-scale

A facile and efficient approach to the synthesis of imidazo[1,5-c]quinazolines was developed via a tandem reaction following dual sp³ C–H amination under metal-free conditions.

Design, synthesis and biological evaluation of novel 7-mercaptocoumarin derivatives as α(1)-adrenoceptor antagonists

Study on the pharmacophore model of α(1)-adrenoceptor (α(1)-AR) antagonists led to design a series of novel 7-mercaptocoumarin derivatives as α(1)-AR antagonists. All designed compounds have been synthesized and biologically evaluated. The results showed that most of them exhibited strong antagonistic activity. Especially compound 6 showed excellent activity, which was better than that of the reference compound prazosin. Structure-activity relationship studies revealed that small hydrophobic group at the terminal heterocyclic ring and ortho substituents on the phenyl ring of phenylpiperazine moiety were the essential structural factors for α(1)-AR antagonistic activity. The pharmacophore modeling studies further clarified their structural contributions to antagonistic activity and also demonstrated that 7-mercaptocoumarin moiety could be a useful scaffold for design of α(1)-AR antagonists.

Structure-Activity Relationship Studies of a Number of α1 -Adrenoceptor Antagonists and Antiarrhythmic Agents

Arylpiperazines represent one of the most studied classes of α1 -adrenoceptor (α1 -AR) antagonists. Currently, α1 -AR antagonists are useful in the treatment of benign prostatic hyperplasia, lower urinary tract symptoms or cardiac arrhythmia. The activity of various derivatives of 1-[3-(4-arylpiperazin-1-yl)propyl]pyrrolidin-2-one as α1 -adrenergic receptor antagonists and antiarrhythmic (AA) agents was described using the qualitative inverse Structure Activity Relationship (SAR) model. The three-dimensional structures of the pyrrolidin-2-one derivatives in the basic form were obtained using AM1 semi-empirical quantum chemical calculations. All the molecules were geometry-optimized until the root-mean-square (RMS) gradient value was smaller than 10(-6) a.u. Single-point energy (SPE) calculations were performed at the DFT/B3LYP level of theory using the 6-31G** basis set. The main focus of this inverse SAR study is to find which features cause enhancing of antiarrhythmic properties between subtly different types of activity (α1 -adrenoreceptor antagonists and antiarrhythmic activities). Our SAR study involves the charge distribution in the plane of the pharmacophore model for α1 -AR. Suitable maps of the electrostatic potential were plotted based on the electronic and nuclear charge distribution obtained from the energy calculations. The results of this modelling study indicate that if the terminal arylpiperazine moiety is surrounded by regions of negative electrostatic potential, then the antiarrhythmic activity is blocked.

Synthesis and Pharmacological Evaluation of New 1-[3-(4-Arylpiperazin-1-yl)-2-hydroxypropyl]-pyrrolidin-2-one Derivatives with Anti-arrhythmic, Hypotensive, and α-Adrenolytic Activity

A series of novel arylpiperazines bearing a pyrrolidin-2-one fragment was synthesized and evaluated for the binding affinity of the alpha(1)- and alpha(2)-adrenoceptors (AR) and for the antiarrhythmic and hypotensive activities of the compounds. The most potent and selective compound 1-[2-hydroxy-3-[4-[(2-hydroxyphenyl)piperazin-1-yl]propyl]pyrrolidin-2-one 8 binds with pK(i) = 6.71 for alpha(1)-AR. Derivative 8 was also the most active in the prophylactic antiarrhythmic test in adrenaline-induced arrhythmia in anaesthetized rats. Its ED(50 )value equals 1.9 mg/kg (i.v.). Compounds with substituents such as a fluorine atom 4, a methyl 5, or a hydroxyl 8 group, or two substituents such as fluorine/chlorine atoms and methoxy groups in the phenyl ring, significantly decreased the systolic and diastolic pressure in normotensive anesthetized rats at a dosages of 5-10 mg/kg (i.v.). It was found that the presence of the piperazine ring and a hydroxy group in the second position of the propyl chain are critical structural features in determining the affinity of the compounds tested.