Structural design, synthesis and substituent effect of hydrazone-N-acylhydrazones reveal potent immunomodulatory agents

Abstract

4-(Nitrophenyl)hydrazone derivatives of N-acylhydrazone were synthesized and screened for suppress lymphocyte proliferation and nitrite inhibition in macrophages. Compared to an unsubstituted N-acylhydrazone, active compounds were identified within initial series when hydroxyl, chloride and nitro substituents were employed. Structure-activity relationship was further developed by varying the position of these substituents as well as attaching structurally-related substituents. Changing substituent position revealed a more promising compound series of anti-inflammatory agents. In contrast, an N-methyl group appended to the 4-(nitrophenyl)hydrazone moiety reduced activity. Anti-inflammatory activity of compounds is achieved by modulating IL-1b secretion and prostaglandin E2 synthesis in macrophages and by inhibiting calcineurin phosphatase activity in lymphocytes. Compound SintMed65 was advanced into an acute model of peritonitis in mice, where it inhibited the neutrophil infiltration after being orally administered. In summary, we demonstrated in great details the structural requirements and the underlying mechanism for anti-inflammatory activity of a new family of hydrazone-N-acylhydrazone, which may represent a valuable medicinal chemistry direction for the anti-inflammatory drug development in general.

Synthesis of Novel N-Acylhydrazones and Their C-N/N-N Bond Conformational Characterization by NMR Spectroscopy

“…Aromatic protons exhibited signals between 7.62 and 8.56 ppm among which H-4 of the pyrazolo [3,4-b]quinoline ring emerged as the most deshielded proton. In the 13 C NMR spectrum of the compound 3, signals for carbonyl carbon and -OCH3 group of ester were observed at 169.3 and 52.8 ppm, respectively, while methylene carbon showed up at 48.3 ppm.…”

“…Until now, the researchers have focused on stereoisomers arising from C=N and C(O)-NH bond rotation; however, rotation about the N-N bond remained overlooked. In this study, we demonstrate the synthesis and investigation of the stereochemical behavior of new N-acylhydrazones of 2-(6-Methyl-1H-pyrazolo [3,4-b]quinolin-1-yl)acetohydrazide by interpretation of the signal duplication in their 1 H NMR and 13 C NMR spectra in DMSO-d 6 solvent. Since the comprehensive information including stereochemistry of a molecule is very important for optimization in drug design and discovery; the conformers arising from rotation around N-N bond too have been considered to depict a clear picture of the steric factors.…”

“…Hydrazinolysis of the synthesized ester (3) resulted in the formation of 2-(6-methyl-1H-pyrazolo [3,4-b]quinolin-1-yl)acetohydrazide (4), which was finally condensed with a variety of aromatic aldehydes 5(a-t) in acidic conditions to afford titled N-acylhydrazones 6(a-t) in 82-99% yield. The progress of reaction was monitored by TLC and structures of the synthesized compounds 6(a-t) were elucidated using different techniques including FT-IR, 1 H NMR, 13 C NMR spectroscopies and mass spectrometry (see Supplementary Materials). The purity of the titled compounds was established from elemental analysis.…”

“…This moiety is a putative bioisostere of amide backbone [9]. Its achiral nature and higher chemical stability than peptide bond have urged the medicinal chemists to consider this privileged scaffold for structural design of new drug candidates [10][11][12][13][14][15][16]. Due to the presence of H-bonding sites and viability of adopting multiple conformational orientations, N-acylhydrazones have a promising prospective to interact with various bioreceptors.…”

“…Rotation along imine C=N linkage may give rise to two geometrical stereoisomers, i.e., E and Z forms. By means of 1 H-and 13 C NMR data, Palla and coworkers speculated that N-Acyl hydrazones of aromatic aldehydes tend to exist in E configuration in solid form [21]. In solution too, the less hindered E is the preferred geometry; however, the Z isomer can be detected in fewer polar solvents [22,23].…”