Convenient methods for preparing pi-conjugated linkers as building blocks for modular chemistry

AiZynth impact on medicinal chemistry practice at AstraZeneca

AstraZeneca chemists have been using the AI retrosynthesis tool AiZynth for three years. In this article, we present seven examples of how medicinal chemists using AiZynth positively impacted their drug discovery programmes. These programmes run the gamut from early-stage hit confirmation to late-stage route optimisation efforts. We also discuss the different use cases for which AI retrosynthesis tools are best suited.

Towards a Light-mediated Gene Therapy for the Eye using Caged Ethinylestradiol and the Inducible Cre/lox System

Increasingly, retinal pathologies are being treated with virus-mediated gene therapies. To be able to target viral transgene expression specifically to the pathological regions of the retina with light, we established an in vivo photoactivated gene expression paradigm for retinal tissue. Based on the inducible Cre/lox system, we discovered that ethinylestradiol is a suitable alternative to Tamoxifen as ethinylestradiol is more amenable to modification with photosensitive protecting compounds, i.e., "caging." Identification of ethinylestradiol as a ligand for the mutated human estradiol receptor was supported by in silico binding studies showing the reduced binding of caged ethinylestradiol. Caged ethinylestradiol was injected into the eyes of double transgenic GFAP-CreERT2 mice with a Cre-dependent tdTomato reporter transgene followed by irradiation with light of 450 nm. Photoactivation significantly increased retinal tdTomato expression compared to controls. We thus demonstrated a first step towards the development of a targeted, light-mediated gene therapy for the eyes.

Photoactivatable Liposomes for Blue to Deep Red Light-Activated Surface Drug Release: Application to Controlled Delivery of the Antitumoral Drug Melphalan

Liposome-based nanoparticles able to release, via a photolytic reaction, a payload anchored at the surface of the phospholipid bilayer were prepared. The liposome formulation strategy uses an original drug-conjugated blue light-sensitive photoactivatable coumarinyl linker. This is based on an efficient blue light-sensitive photolabile protecting group modified by a lipid anchor, which enables its incorporation into liposomes, leading to blue to green light-sensitive nanoparticles. In addition, the formulated liposomes were doped with triplet-triplet annihilation upconverting organic chromophores (red to blue light) in order to prepare red light sensitive liposomes able to release a payload, by upconversion-assisted photolysis. Those light-activatable liposomes were used to demonstrate that direct blue or green light photolysis or red light TTA-UC-assisted drug photolysis can effectively photorelease a drug payload (Melphalan) and kill tumor cells in vitro after photoactivation.

Red Light-Responsive Upconverting Nanoparticles for Quantitative and Controlled Release of a Coumarin-Based Prodrug

Photolytic reactions allow the optical control of the liberation of biological effectors by photolabile protecting groups. The development of versatile technologies enabling the use of deep-red or NIR light excitation still represents a challenging issue, in particular for light-induced drug release (e.g., light-induced prodrug activation). Here, light-sensitive biocompatible lipid nanocapsules able to liberate an antitumoral drug through photolysis are presented. It is demonstrated that original photon upconverting nanoparticles (LNC-UCs) chemically conjugated to a coumarin-based photocleavable linker can quantitatively and efficiently release a drug by upconversion luminescence-assisted photolysis using a deep-red excitation wavelength. In addition, it is also able to demonstrate that such nanoparticles are stable in the dark, without any drug leakage in the absence of light. These findings open new avenues to specifically liberate diverse drugs using deep-red or NIR excitations for future therapeutic applications in nanomedicine.

Merging Iridium-Catalyzed C-H Borylations with Palladium-Catalyzed Cross-Couplings Using Triorganoindium Reagents

A versatile and efficient method to prepare borylated arenes furnished with alkyl, alkenyl, alkynyl, aryl, and heteroaryl functional groups is developed by merging Ir-catalyzed C-H borylations (CHB) with a chemoselective palladium-catalyzed cross-coupling of triorganoindium reagents (Sarandeses-Sestelo coupling) with aryl halides bearing a boronic ester substituent. Using triorganoindium cross-coupling reactions to introduce unsaturated moieties enables the synthesis of borylated arenes that would be difficult to access through the direct application of the CHB methodology. The sequential double catalyzed procedure can be also performed in one vessel.

Quaternary Ammonium Compounds: Simple in Structure, Complex in Application

Quaternary ammonium compounds, referred to as QACs, are cationic substances with a structure on the edge of organic and inorganic chemistry and unique physicochemical properties. The purpose of the present work is to introduce QACs and their wide application potential. Fundamental properties, methods of preparation, and utilization in organic synthesis are reviewed. Modern applications and the use of QACs as reactive substrates, reagents, phase-transfer catalysts, ionic liquids, electrolytes, frameworks, surfactants, herbicides, and antimicrobials are further covered. A brief discussion of the health and environmental impact of QACs is also provided. The emphasis is largely on tetraalkylammonium compounds bearing linear alkyl chains.

Dicyanobenzene and dicyanopyrazine derived X-shaped charge-transfer chromophores: comparative and structure-property relationship study

A series of novel X-shaped push-pull compounds based on benzene-1,2-dicarbonitrile has been designed, synthesized and further investigated by X-ray analysis, electrochemistry, absorption and emission spectra, SHG experiment and quantum-chemical calculations. The obtained data were compared with those for isolobal 5,6-disubstituted pyrazine-2,3-dicarbonitriles. Structure-property relationships were elucidated. The extension, composition and planarization of the π-linker used as well as the electron-withdrawing ability of both dicyano-substituted acceptor units affect the linear and nonlinear properties of the target charge-transfer chromophores most significantly.

Synthesis and optical properties of novel D–π–A–π–D type cationic cyclopentadienyliron complexes of arenes

With the enlarged and annulated ICT conjugation systems, three new cationic cyclopentadienyliron complexes exhibited significantly better third-order NLO absorption properties than the commercial cyclopentadienyliron arene complexes I-261.

Conjugated aromatic asymmetrical terpyridine analogues via step-wise photocyclization and their ruthenium complexes

Asymmetrical conjugated terpyridines were acquired by the UV irradiation. Step oxidative cyclodehydrogenation along with the aromatic conjugation expansion was proved with the intermediates isolations. The terpyridine Ru²⁺ dimerizations were successfully introduced.

Imidazole as a parent π-conjugated backbone in charge-transfer chromophores

Research activities in the field of imidazole-derived push-pull systems featuring intramolecular charge transfer (ICT) are reviewed. Design, synthetic pathways, linear and nonlinear optical properties, electrochemistry, structure-property relationships, and the prospective application of such D-π-A organic materials are described. This review focuses on Y-shaped imidazoles, bi- and diimidazoles, benzimidazoles, bis(benzimidazoles), imidazole-4,5-dicarbonitriles, and imidazole-derived chromophores chemically bound to a polymer chain.

Effects of the nature and length of the π-conjugated bridge on the second-order nonlinear optical responses of push-pull molecules including 4,5-dicyanoimidazole and their protonated forms

Theoretical and experimental methods of characterization have been employed to investigate a series of six push-pull molecules containing a 4,5-dicyanoimidazole acceptor (A) unit, a N,N-dimethylamino donor (D) group, and systematically enlarged π-conjugated linkers (π) with the view of assessing their first hyperpolarizabilities (β) as well as their variations upon protonation. The results demonstrated that protonation occurred at the N,N-dimethylamino function, which led to disruption of the electronic charge-transfer delocalization: the A-π-D pattern of the neutral species with large β values was transformed into an A-π-A' pattern, which displayed much smaller β values. This feature makes these systems applicable as pH-triggered nonlinear optics (NLO) switches. In particular, protonation led to a decrease of the hyper-Rayleigh scattering first hyperpolarizabilities by at least one order of magnitude as well as to a decrease of the depolarization ratio, from about five for neutral species, which also supported the 1D-like NLO-phore nature, to about two for the protonated ones.

Optical operation by chromophores featuring 4,5-dicyanoimidazole embedded within poly(methyl methacrylate) matrices

We have studied photoinduced absorption, birefringence, and optical second-harmonic generation in poly(methyl methacrylate) (PMMA) films doped by organic chromophores featuring 4,5-dicyanoimidazole in the weight content equal to 5%. The chromophores indicated as IM1-IM6 were synthesized from 2-bromo-1-methylimidazole-4,5-dicarbonitrile by either nucleophilic substitution or Suzuki-Miyaura cross-coupling reaction. The samples were obtained as films of several micrometers thickness by the spin-coating method on a quartz substrate. Measurements of the optically induced birefringence were done by the Senarmont method at wavelength 1150 nm, and photoinduced absorption was studied in the spectral range 250-700 nm under optical treatment by 300 mW cw 532 nm laser. Photoinduced optical effects were studied by bicolor 1064 and 532 nm coherent laser pulses. The maximal changes were observed for the ratio between fundamental and writing beam intensities equal to about 7:1. To interpret the observed experimental measurements, theoretical simulations of photoinduced optical properties were performed by quantum chemical computational methods.