Conformational studies of tertiary oligo-m-benzanilides and oligo-p-benzanilides in solution

Atropisomeric Foldamers

This concept article explores the emerging role of atropisomerism in foldamer chemistry, a field focussed on oligomers that adopt well-defined conformations through non-covalent interactions. Atropisomerism introduces a novel dimension to foldamer design by restricting rotational freedom around single bonds to dictate molecular shape with precision. Despite the prevalence of atropisomeric bonds in organic synthesis, their application within foldamers remains underexplored. Here, we discuss key developments in both backbone and sidechain atropisomerism, and suggest future directions for atropisomeric foldamers in the context of a recent surge in atropselective synthetic methods. We propose that judicious use of atropisomerism may serve as a transformative tool in the construction of shape-defined macromolecules.

Synthesis and the In Vitro Evaluation of Antitumor Activity of Novel Thiobenzanilides

Cancer is a generic term for a large group of diseases that are the second-leading cause of death worldwide, accounting for nearly 10 million deaths in 2020. Melanoma is a highly aggressive skin tumor with an increasing incidence and poor prognosis in the metastatic stage. Breast cancer still stands as one of the major cancer-associated deaths among women, and diagnosed cases are increasing year after year worldwide. Despite the recent therapeutic advances for this type of cancer, novel drugs and treatment strategies are still urgently needed. In this paper, the synthesis of 18 thiobenzanilide derivatives (17 of them new) is described, and their cytotoxic potential against melanoma cells (A375) and hormone-dependent breast cancer (MCF-7) cells is evaluated using the MTT assay. In the A375 cell line, most of the tested thiobenzanilides derivatives showed EC₅₀ values in the order of μM. Compound 17 was the most promising, with an EC₅₀ (24 h) of 11.8 μM. Compounds 8 and 9 are also interesting compounds that deserve to be further improved. The MCF-7 cell line, on the other hand, was seen to be less susceptible to these thiobenzanilides indicating that these compounds show different selectivity towards skin and breast cancer cells. Compound 15 showed the highest cytotoxic potential for MCF-7 cells, with an EC₅₀ (24 h) of 43 μM, a value within the range of the EC₅₀ value determined for tamoxifen (30.0 μM). ADME predictions confirm the potential of the best compounds. Overall, this work discloses a new set of thiobenzanilides that are worth being considered as new scaffolds for the further development of anticancer agents.

Using Lateral Substitution to Control Conformational Preference and Phase Behaviour of Benzanilide-based Liquid Crystal Dimers

The inclusion of secondary and tertiary benzanilide-based mesogenic groups into liquid crystal dimers is reported as a means to develop new materials. Furthermore, substitution at the nitrogen atom is shown to introduce an additional synthetic 'handle' to modify the molecular structure of the tertiary materials. The design of these materials has proved challenging due to the strong preferences of 3° benzanilides for the E amide conformation. In this work, lateral substitution is used to modify the conformational preferences of the amide linkage and promote liquid crystallinity for a series of N-methyl benzanilide dimers. As the proportion of the E conformer decreases, the nematic-isotropic transition temperatures increase, and enantiotropic nematic behaviour is observed. We also report the synthesis and characterisation of the analogous 2° benzanilide-based materials, which show nematic and twist-bend nematic behaviour. This approach highlights the effects that seemingly small structural modifications, such as the inclusion and position of a methyl group, can have on molecular shape and hence, liquid crystalline behaviour.

N-Alkylated Aromatic Poly- and Oligoamides

N-alkylated aromatic poly- and oligoamides are a particular class of abiotic foldamers that is deprived of the capability of forming intramolecular hydrogen-bonding networks to stabilize their tri-dimensional structure. The alkylation of the backbone amide nitrogen atoms greatly increases the chemical diversity accessible for aromatic poly- and oligoamides. However, the nature and the conformational preferences of the N,N-disubstituted amides profoundly modify the folding properties of these aromatic poly- and oligoamides. In this Review, representative members of this class of aromatic poly- and oligoamides will be highlighted, among them N-alkylated phenylene terephthalamides, benzanilides, pyridylamides, and aminomethyl benzamide oligomers. The principal synthetic pathways to the main classes of N-alkylated aromatic polyamides with narrow to broad molecular-weight distribution, or oligoamides with specific sequences, will be detailed and their foldameric properties will be discussed. The Review will end by describing the few applications reported to date and future prospects for the field.

Understanding the remarkable difference in liquid crystal behaviour between secondary and tertiary amides: the synthesis and characterisation of new benzanilide-based liquid crystal dimers

A number of liquid crystal dimers have been synthesised and characterised containing secondary or tertiary (N-methyl) benzanilide-based mesogenic groups. The secondary amides all form nematic phases, and we present the first example of an amide to show the twist-bend nematic (NTB) phase. Only two of the corresponding N-methylated dimers formed a nematic phase and with greatly reduced nematic-isotropic transition temperatures. Characterisation using 2D ROESY NMR experiments, DFT geometry optimisation and X-ray diffraction reveal that there is a change in the preferred conformation of the benzanilide core on methylation, from Z to E. The rotational barrier around the N-C(O) bond has been measured using variable temperature 1H NMR spectroscopy. This dramatic change in shape accounts for the remarkable difference in liquid crystalline behaviour between these secondary and tertiary amide-based materials.

Characterization of Conformationally Constrained Benzanilide Scaffolds for Potent and Selective HDAC8 Targeting

Histone deacetylases (HDACs) are an attractive therapeutic target for a variety of human diseases. Currently, all four FDA-approved HDAC-targeting drugs are nonselective, pan-HDAC inhibitors, exhibiting adverse side effects at therapeutic doses. Although selective HDAC inhibition has been proposed to mitigate toxicity, the targeted catalytic domains are highly conserved. Herein, we describe a series of rationally designed, conformationally constrained, benzanilide foldamers which selectively bind the catalytic tunnel of HDAC8. The series includes benzanilides, MMH371, MMH409, and MMH410, which exhibit potent in vitro HDAC8 activity (IC₅₀ = 66, 23, and 66 nM, respectively) and up to 410-fold selectivity for HDAC8 over the next targeted HDAC. Experimental and computational analyses of the benzanilide structure docked with human HDAC8 enzyme showed the adoption of a low-energy L-shaped conformer that favors HDAC8 selectivity. The conformationally constrained HDAC8 inhibitors present an alternative biological probe for further determining the clinical utility and safety of pharmacological knockdown of HDAC8 in diseased cells.

Design, Synthesis, and Conformational Analysis of Oligobenzanilides as Multifacial α-Helix Mimetics

The design, synthesis, and conformational analysis of an oligobenzanilide helix mimetic scaffold capable of simultaneous mimicry of two faces of an α-helix is reported. The synthetic methodology provides access to diverse monomer building blocks amenable to solid-phase assembly in just four synthetic steps. The conformational flexibility of model dimers was investigated using a combination of solid and solution state methodologies supplemented with DFT calculations. The lack of noncovalent constraints allows for significant conformational plasticity in the scaffold, thus permitting it to successfully mimic residues i, i+2, i+4, i+6, i+7, and i+9 of a canonical α-helix.

Deciphering the mechanism of copper-catalyzed N-arylation between aryl halides and nitriles: a DFT study

The mechanism of the CuI/DMEDA-catalyzed tandem hydrolysis/N-arylation of benzonitrile with aryl iodide was studied using the DFT method.

Chiroptical molecular propellers based on hexakis(phenylethynyl)benzene through the complexation-induced intramolecular transmission of local point chirality

We designed hexakis(phenylethynyl)benzene derivatives with a tertiary amide group on each blade to achieve a helically biased propeller arrangement.