Structure-based design, synthesis, and biological evaluation of lipophilic-tailed monocationic inhibitors of neuronal nitric oxide synthase

Synergistic Effect of Sophora japonica and Glycyrrhiza glabra Flavonoid-Rich Fractions on Wound Healing: In Vivo and Molecular Docking Studies

Glycyrrhiza glabra and Sophora japonica (Fabaceae) are well-known medicinal plants with valuable secondary metabolites and pharmacological properties. The flavonoid-rich fractions of G. glabra roots and S. japonica leaves were prepared using Diaion column chromatography, and the confirmation of flavonoid richness was confirmed using UPLC-ESI-MS profiling and total phenolics and flavonoids assays. UPLC-ESI-MS profiling of the flavonoid-rich fraction of G. glabra roots and S. japonica leaves resulted in the tentative identification of 32 and 23 compounds, respectively. Additionally, the wound healing potential of topical preparations of each fraction, individually and in combination (1:1) ointment and gel preparations, were investigated in vivo, supported by histopathological examinations and biomarker evaluations, as well as molecular docking studies for the major constituents. The topical application of G. glabra ointment and gel, S. japonica ointment and gel and combination preparations significantly increase the wound healing rate and the reduction of oxidative stress in the wound area via MDA reduction and the elevation of reduced GSH and SOD levels as compared to the wound and Nolaver®-treated groups. The molecular docking study revealed that that major compounds in G. glabra and S. japonica can efficiently bind to the active sites of three proteins related to wound healing: glycogen synthase kinase 3-β (GSK3-β), matrix metalloproteinases-8 (MMP-8) and nitric oxide synthase (iNOS). Consequently, G. glabra roots and S. japonica leaves may be a rich source of bioactive metabolites with antioxidant, anti-inflammatory and wound healing properties.

Recent Advances in the Synthesis and Applications of m-Aryloxy Phenols

Since phenol derivatives have high potential as building blocks for the synthesis of bioactive natural products and conducting polymers, many synthesis methods have been invented. In recent years, innovative synthetic methods have been developed for the preparation of m-aryloxy phenols, which has allowed for the preparation of complex m-aryloxy phenols with functional groups, such as esters, nitriles, and halogens, that impart specific properties of these compounds. This review provides an overview of recent advances in synthetic strategies for m-aryloxy phenols and their potential biological activities. This paper highlights the importance of m-aryloxy phenols in various industries, including plastics, adhesives, and coatings, and it discusses their applications as antioxidants, ultraviolet absorbers, and flame retardants.

Comparative Metabolic Study of Tamarindus indica L.'s Various Organs Based on GC/MS Analysis, In Silico and In Vitro Anti-Inflammatory and Wound Healing Activities

The chemical composition of the n-hexane extract of Tamarindus indica's various organs-bark, leaves, seeds, and fruits (TIB, TIL, TIS, TIF)-was investigated using gas chromatography-mass spectrometry (GC/MS) analysis. A total of 113 metabolites were identified, accounting for 93.07, 83.17, 84.05, and 85.08 % of the total identified components in TIB, TIL, TIS, and TIF, respectively. Lupeol was the most predominant component in TIB and TIL, accounting for 23.61 and 22.78%, respectively. However, n-Docosanoic acid (10.49%) and methyl tricosanoate (7.09%) were present in a high percentage in TIS. However, α-terpinyl acetate (7.36%) and α-muurolene (7.52%) were the major components of TIF n-hexane extract. By applying a principal component analysis (PCA) and hierarchal cluster analysis (HCA) to GC/MS-based metabolites, a clear differentiation of Tamarindus indica organs was achieved. The anti-inflammatory activity was evaluated in vitro on lipopolysaccharide (LPS)-induced RAW 264.7 macrophages. In addition, the wound healing potential for the n-hexane extract of various plant organs was assessed using the in-vitro wound scratch assay using Human Skin Fibroblast cells. The tested extracts showed considerable anti-inflammatory and wound-healing activities. At a concentration of 10 µg/mL, TIL showed the highest nitric oxide (NO) inhibition by 53.97 ± 5.89%. Regarding the wound healing potential, after 24 h, TIB, TIL, TIS, and TIF n-hexane extracts at 10 g/mL reduced the wound width to 1.09 ± 0.04, 1.12 ± 0.18, 1.09 ± 0.28, and 1.41 ± 0.35 mm, respectively, as compared to the control cells (1.37 ± 0.15 mm). These findings showed that the n-hexane extract of T. indica enhanced wound healing by promoting fibroblast migration. Additionally, a docking study was conducted to assess the major identified phytoconstituents' affinity for binding to glycogen synthase kinase 3-β (GSK3-β), matrix metalloproteinases-8 (MMP-8), and nitric oxide synthase (iNOS). Lupeol showed the most favourable binding affinity to GSK3-β and iNOS, equal to -12.5 and -13.7 Kcal/mol, respectively, while methyl tricosanoate showed the highest binding affinity with MMP-8 equal to -13.1 Kcal/mol. Accordingly, the n-hexane extract of T. indica's various organs can be considered a good candidate for the management of wound healing and inflammatory conditions.

Discovery of a Colon-Targeted Azo Prodrug of Tofacitinib through the Establishment of Colon-Specific Delivery Systems Constructed by 5-ASA-PABA-MAC and 5-ASA-PABA-Diamine for the Treatment of Ulcerative Colitis

To mitigate the systemic adverse effects of tofacitinib, 5-ASA-PABA-MAC and 5-ASA-PABA-diamine colon-specific delivery systems were constructed, and tofacitinib azo prodrugs 9 and 20a-20g were synthesized accordingly. The release studies suggested that these systems could effectively release tofacitinib in vitro, and the 5-ASA-PABA-diamine system could successfully realize the colon targeting of tofacitinib in vivo. Specifically, compound 20g displayed a 3.67-fold decrease of plasma AUC_{(tofacitinib, 0-∞)} and a 9.61-fold increase of colonic AUC_{(tofacitinib, 0-12h)}, compared with tofacitinib at a molar equivalent oral dose. Moreover, mouse models suggested that compound 20g (1.5 mg/kg) could achieve roughly the same efficacy against ulcerative colitis compared with tofacitinib (10 mg/kg) and did not impair natural killer cells. These results demonstrated the feasibility of compound 20g as an effective alternative to mitigate the systemic adverse effects of tofacitinib, and 5-ASA-PABA-MAC and 5-ASA-PABA-diamine systems were proven to be effective for colon-specific drug delivery.

Development of nitric oxide synthase inhibitors for neurodegeneration and neuropathic pain

Nitric oxide (NO) is an important signaling molecule in the human body, playing a crucial role in cell and neuronal communication, regulation of blood pressure, and in immune activation. However, overproduction of NO by the neuronal isoform of nitric oxide synthase (nNOS) is one of the fundamental causes underlying neurodegenerative disorders and neuropathic pain. Therefore, developing small molecules for selective inhibition of nNOS over related isoforms (eNOS and iNOS) is therapeutically desirable. The aims of this review focus on the regulation and dysregulation of NO signaling, the role of NO in neurodegeneration and pain, the structure and mechanism of nNOS, and the use of this information to design selective inhibitors of this enzyme. Structure-based drug design, the bioavailability and pharmacokinetics of these inhibitors, and extensive target validation through animal studies are addressed.

Recent advances toward improving the bioavailability of neuronal nitric oxide synthase inhibitors

Overproduction of nitric oxide by neuronal nitric oxide synthase (nNOS) has been highly correlated with numerous neurodegenerative diseases and stroke. Given its role in human diseases, nNOS is an important target for therapy that deserves further attention. During the last decade, a large number of organic scaffolds have been investigated to develop selective nNOS inhibitors, resulting in two principal classes of compounds, 2-aminopyridines and thiophene-2- carboximidamides. The former compounds were investigated in detail by our group, exhibiting great potency and excellent selectivity; however, they suffer from poor bioavailability, which hampers their therapeutic potential. Here we present a review of various strategies adopted by our group to improve the bioavailability of 2-aminopyridine derivatives and describe recent advances in thiophene-2-carboximidamide based nNOS-selective inhibitors, which exhibit promising pharmacological profiles.

Simplified 2-aminoquinoline-based scaffold for potent and selective neuronal nitric oxide synthase inhibition

Since high levels of nitric oxide (NO) are implicated in neurodegenerative disorders, inhibition of the neuronal isoform of nitric oxide synthase (nNOS) and reduction of NO levels are therapeutically desirable. Nonetheless, many nNOS inhibitors mimic l-arginine and are poorly bioavailable. 2-Aminoquinoline-based scaffolds were designed with the hope that they could (a) mimic aminopyridines as potent, isoform-selective arginine isosteres and (b) possess chemical properties more conducive to oral bioavailability and CNS penetration. A series of these compounds was synthesized and assayed against purified nNOS enzymes, endothelial NOS (eNOS), and inducible NOS (iNOS). Several compounds built on a 7-substituted 2-aminoquinoline core are potent and isoform-selective; X-ray crystallography indicates that aminoquinolines exert inhibitory effects by mimicking substrate interactions with the conserved active site glutamate residue. The most potent and selective compounds, 7 and 15, were tested in a Caco-2 assay and showed good permeability and low efflux, suggesting high potential for oral bioavailability.

Cyclopropyl- and methyl-containing inhibitors of neuronal nitric oxide synthase

Inhibitors of neuronal nitric oxide synthase have been proposed as therapeutics for the treatment of different types of neurological disorders. On the basis of a cis-3,4-pyrrolidine scaffold, a series of trans-cyclopropyl- and methyl-containing nNOS inhibitors have been synthesized. The insertion of a rigid electron-withdrawing cyclopropyl ring decreases the basicity of the adjacent amino group, which resulted in decreased inhibitory activity of these inhibitors compared to the parent compound. Nonetheless, three of them exhibited double-digit nanomolar inhibition with high nNOS selectivity on the basis of in vitro enzyme assays. Crystal structures of nNOS and eNOS with these inhibitors bound provide a basis for detailed structure-activity relationship (SAR) studies. The conclusions from these studies will be used as a guide in the future development of selective NOS inhibitors.

Intramolecular hydrogen bonding: a potential strategy for more bioavailable inhibitors of neuronal nitric oxide synthase

Selective neuronal nitric oxide synthase (nNOS) inhibitors have therapeutic applications in the treatment of numerous neurodegenerative diseases. Here we report the synthesis and evaluation of a series of inhibitors designed to have increased cell membrane permeability via intramolecular hydrogen bonding. Their potencies were examined in both purified enzyme and cell-based assays; a comparison of these results demonstrates that two of the new inhibitors display significantly increased membrane permeability over previous analogs. NMR spectroscopy provides evidence of intramolecular hydrogen bonding under physiological conditions in two of the inhibitors. Crystal structures of the inhibitors in the nNOS active site confirm the predicted non-intramolecular hydrogen bonded binding mode. Intramolecular hydrogen bonding may be an effective approach for increasing cell membrane permeability without affecting target protein binding.

Acid-Facilitated Debenzylation of N-Boc, N-Benzyl Double Protected 2-Aminopyridinomethylpyrrolidine Derivatives

2-Aminopyridinomethyl pyrrolidines represent a class of highly potent and selective neuronal nitric oxide synthase inhibitors. Conditions for a Mitsunobu reaction of a naphthol and a hindered secondary alcohol were optimized to give good to excellent yields. A key step in the synthesis of these inhibitors is the deprotection of the benzyl group from the N-Boc and N-Bn double protected 2-aminopyridine ring at a late stage of the synthesis, which has been proven difficult in our previous syntheses. Acetic acid was found to facilitate the N-Bn deprotection.

Symmetric double-headed aminopyridines, a novel strategy for potent and membrane-permeable inhibitors of neuronal nitric oxide synthase

We report novel neuronal nitric oxide synthase (nNOS) inhibitors based on a symmetric double-headed aminopyridine scaffold. The inhibitors were designed from crystal structures of leads 1 and 2 (Delker, S. L.; Ji, H.; Li, H.; Jamal, J.; Fang, J.; Xue, F.; Silverman, R. B.; Poulos, T. L. Unexpected binding modes of nitric oxide synthase inhibitors effective in the prevention of cerebral palsy . J. Am. Chem. Soc. 2010, 132, 5437-5442) and synthesized using a highly efficient route. The best inhibitor, 3j, showed low nanomolar inhibitory potency and modest isoform selectivity. It also exhibited enhanced membrane permeability. Inhibitor 3j binds to both the substrate site and the pterin site in nNOS but only to the substrate site in eNOS. These compounds provide a basis for further development of novel, potent, isoform selective, and bioavailable inhibitors for nNOS.

Potent, highly selective, and orally bioavailable gem-difluorinated monocationic inhibitors of neuronal nitric oxide synthase

In our efforts to discover neuronal isoform selective nitric oxide synthase (NOS) inhibitors, we have developed a series of compounds containing a pyrrolidine ring with two stereogenic centers. The enantiomerically pure compounds, (S,S) versus (R,R), exhibited two different binding orientations, with (R,R) inhibitors showing much better potency and selectivity. To improve the bioavailability of these inhibitors, we have introduced a CF(2) moiety geminal to an amino group in the long tail of one of these inhibitors, which reduced its basicity, resulting in compounds with monocationic character under physiological pH conditions. Biological evaluations have led to a nNOS inhibitor with a K(i) of 36 nM and high selectivity for nNOS over eNOS (3800-fold) and iNOS (1400-fold). MM-PBSA calculations indicated that the low pK(a) NH is, at least, partially protonated when bound to the active site. A comparison of rat oral bioavailability of the difluorinated compound to the parent molecule shows 22% for the difluorinated compound versus essentially no oral bioavailability for the parent compound. This indicates that the goal of this research to make compounds with only one protonated nitrogen atom at physiological pH to allow for membrane permeability, but which can become protonated when bound to NOS, has been accomplished.