Solvent-dependent conformational switching of the aromatic N-methyl amides depending upon the acceptor properties of solvents

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.

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.

N-Methylamino Pyrimidyl Amides (MAPA): Highly Reactive, Electronically-Activated Amides in Catalytic N-C(O) Cleavage

Despite recent progress in catalytic cross-coupling technologies, the direct activation of N-alkyl-N-aryl amides has been a challenging transformation. Here, we report the first Suzuki cross-coupling of N-methylamino pyrimidyl amides (MAPA) enabled by the controlled n_N → π_Ar conjugation and the resulting remodeling of the partial double bond character of the amide bond. The new mode of amide activation is suitable for generating acyl-metal intermediates from unactivated primary and secondary amides.

Microwave-assisted synthesis and photophysical studies of novel fluorescent N-acylhydrazone and semicarbazone-7-OH-coumarin dyes

Emissive 7-OH-coumarins were synthesized by a microwave-assisted protocol and spectral changes were induced after conformational changes in low polarity media.

Inspired smart materials with external stimuli responsive wettability: a review

Recent progress in smart surfaces with responsive wettability upon external stimuli is reviewed and some of the barriers and potentially promising breakthroughs in this field are also briefly discussed.

Solvent-responsive wettability of self-assembled monolayers of dithiooctanoic acid derivatives bearing N,N-disubstituted amide groups

We have designed and synthesized two dithiooctanoic acid derivatives bearing N,N-disubstituted amide groups and used them to fabricate self-assembled monolayers (SAMs) on gold surface. These films showed a reversible changes in wettability, one of which was indicated by surface contact angle switching between 40° and 59° upon alternating treatment with ethanol and cyclohexane. NMR experimental results of a model molecule suggest that the solvent-responsive wettability of the SAMs could be related with the changes in the relative populations of two stereoisomers of amide. The solvent responsivity of SAMs fabricated from other two amides was also studied, and the results confirmed that N,N-disubstitution was essential for an amide-containing SAM to have stimuli responsivity. Thus, introduction of a functional group exhibiting controlled isomerization of conformation could be an effective strategy for designing new stimuli-responsive materials.

[External stimulus-responsive conformational alterations of aromatic amides]

Three-dimensional structure of a molecule and its alteration is an important issue, and it is essential problem for controlling the function of a molecule such as a molecular switch or device. In most cases, molecular switches have relatively high activation energy for interconversion between alternative structures, however in some biological systems, conformational preference plays an important role in regulation of bioactivity. We have interested in conformational alteration of aromatic amides, which have interesting features about conformation. Most of secondary aromatic amides such as benzanilide tend to prefer trans conformation, whereas N-methylation makes its conformation cis-favored. Recently we found several aromatic amides altered the preferred conformation depending on the external stimuli. Thus, N-phenyl-N-quinonyl type of amides changed their preferred conformation according to redox state of quinonyl moiety. N-Methyl pyridylamides showed conformational alteration according to solvent acceptor ability or addition of acid. N-Methylated pyridylamide oligomer also showed unique conformational folding and unfolding. These properties of the aromatic amides can be applied to stimuli-responsive molecular switches and functional molecules.