Phototriggered Hydrogen Persulfide Donors via Hydrosulfide Radical Formation Enhancing the Reactive Sulfur Metabolome in Cells.

Hydrogen persulfide (H2S2) is an important sulfur-containing signaling molecule that plays a crucial role in the homeostasis of various organ systems, such as the renal, cardiovascular, liver, and gastrointestinal systems. However, research on H2S2 in biological settings is still challenging due to its instability and high reactivity. Compounds that can controllably release H2S2 (also known as donors) are thus crucial research tools. Currently, available H2S2 donors are still very limited, with most of them relying on modified disulfide templates. These templates possess an unavoidable limitation of being susceptible to cellular disulfide exchange which can compromise their efficacy. In this work, we explored nondisulfide-based and nonoxidation-dependent templates for the design of H2S2 donors. We found that tertiary naphthacyl thiols could undergo phototriggered C-S homolytic cleavage to form H2S2 via hydrosulfide (HS) radicals. In addition, the release of H2S2 was associated with the formation of a product with strong blue fluorescence, which allowed for real-time monitoring of the release process. This reaction was demonstrated to proceed effectively in both buffers and cells, with the ability to enhance intracellular production of persulfides, including GSSH, CysSSH, H2S2, H2S3, etc. It provides a unique photocontrolled H2S2 donor system with distinct advantages compared to known H2S2 donors due to its good stability and spatiotemporal control ability.

Oxa-azabenzobenzocyclooctynes (O-ABCs): heterobiarylcyclooctynes bearing an endocyclic heteroatom.

We report the synthesis of heterobiarylcyclooctynes bearing an endocyclic heteroatom, oxa-azabenzobenzocyclooctynes (O-ABCs). The integration of design strategies for accelerating strain-promoted azide-alkyne cycloadditions results in reactivity with organic azides that surpasses all cyclooctyne reagents reported to date. O-ABCs and related compounds provide insights into the effects of structural modifications on reactivity that can aid in the design of new reagents for click and bioorthogonal chemistry.

Regioselective Synthesis of Benzo-Fused Tetrahydroisoquinoline-Based Biaryls through a Tandem One-Pot Halogenation of p-Benzynes from Enediynes and Suzuki-Miyaura Coupling.

A regioselective halogenation of p-benzyne derived from a nonaromatic enediyne core via Bergman cyclization and Suzuki-Miyaura coupling of the resulting haloarene in one-pot is disclosed. For the one-pot protocol to work, the reaction conditions were modified compared to an earlier reported procedure ( J. Org. Chem. 2019 , 84 , 2911 - 2921 ) by reducing the amount of lithium iodide and exclusion of pivalic acid. Under these modified conditions, the products, benzo-fused tetrahydroisoquinoline-based biaryl derivatives were obtained in overall high to excellent yields (71-90%).

Ni(ii)-Catalyzed vinylic C-H functionalization of 2-acetamido-3-arylacrylates to access isotetronic acids.

A ligand-free Ni(ii)-catalyzed cascade annulation reaction for the synthesis of 4-aryl-substituted isotetronic acids from 2-acetamido-3-arylacrylates via vinylic C-H functionalization is reported. The reaction proceeds through heteroatom guided electrophilic insertion of nickel to the vinylic double bond followed by annulation with dibromomethane. This unconventional route features cascade steps, sole product formation, multiple functional group tolerance, low cost of catalysts and reagents, and readily available starting materials. Using this method, various aryl-substituted isotetronic acids have been synthesized which are biologically relevant. The annulation of 2-acetamido-3-arylacrylates has also been assessed with 1,2-dichloroethane, which resulted in the rearranged annulated products of 5-methyl substituted isotetronic acids.

How To Achieve High Regioselectivity in Barrier-less Nucleophilic Addition to p-Benzynes Generated via Bergman Cyclization of Unsymmetrical Cyclic Azaenediyne?

Inducing high regioselectivity in nucleophilic addition to p-benzynes, first reported by Perrin and O'Connor et al. ( J. Am. Chem. Soc. 2007 , 129 , 4795 - 4799 ) has been a challenge as the reaction involves a very fast barrier-less addition of nucleophile. On the other hand, achieving a high degree of regioselectivity is important as that will make the reaction synthetically useful. Recently, a study has been reported from our group ( J. Org. Chem. 2018 , 83 , 7730 - 7740 ), whereby it was shown that nucleophilic addition to p-benzynes derived from unsymmetrical N-substituted cyclic enediynes proceeds with low extent of selectivity by incorporation of groups with divergent electronic characters. Herein, we report that excellent regioselectivity (>99%) can be achieved keeping an ortho alkoxy group in unsymmetrical 1,2-dialkynylbenzene in the form of a cyclic enediyne in quantitative yields. High regioselectivity (∼84%) is also shown by pyridine based enediynes where the pyridine nitrogen is in a 1,3-relationship with the impending radical center, expanding the synthetic scope of this nucleophilic addition. The regioselectivity can be explained in terms of computed electrostatic potentials which are substantially different around two radical centers arising due to the "ortho effect" (conformational alignment of lone pair of the ortho alkoxy oxygen or the nitrogen in pyridine systems).

Experiment and Computational Study on the Regioselectivity of Nucleophilic Addition to Unsymmetrical p-Benzynes Derived from Bergman Cyclization of Enediynes.

The regioselectivity in addition of nucleophiles to the p-benzyne intermediates derived from unsymmetrical aza-substituted enediynes via Bergman cyclization was studied. Computational studies [using UB3LYP/6-31G(d,p) level of theory] suggest that the p-benzyne intermediate retains its similar electrophilic character at the two radical centers even under unsymmetrical electronic perturbation, thus supporting the predicted model of nucleophilic addition to p-benzyne proposed by Perrin and co-workers (Perrin et al. J. Am. Chem. Soc. 2007, 129, 4795-4799) and later by Alabugin and co-workers (Peterson et al. Eur. J. Org. Chem. 2013, 2013, 2505-2527). However, observed experimental results suggest that there was small but definite regioselectivity (∼5-25%), the extent varying with the electronic nature of the substituents. Differential solvated halide ion concentrations around the vicinity of two radical centers arising due to surrounding surface electrostatic potential (computationally calculated) may be one of the possible factors for such selectivity in some of the examined p-benzynes. However, other complicated dynamical issues like the trajectory of the attacking nucleophile to the radical center which can be influenced by electronic and/or steric perturbation of starting enediyne conformation cannot be ruled out. The overall yield of the anionic addition was in the range of 80-99%.

Shifting the Reactivity of Bis-propargyl Ethers from Garratt-Braverman Cyclization Mode to 1,5-H Shift Pathway To Yield 3,4-Disubstituted Furans: A Combined Experimental and Computational Study.

Aryl or vinyl substituted bis-propargyl ethers upon base treatment generally form phthalans via the Garratt-Braverman (GB) cyclization pathway. In a major departure from this usual route, several aryl/vinyl bis-propargyl ethers with one of the acetylenic arms ending up with 2-tetrahydropyranyloxy methyl or ethoxy methyl have been shown to follow the alternative intramolecular 1,5-H shift pathway upon base treatment. The reaction has led to the formation of synthetically as well as biologically important 3,4-disubstituted furan derivatives in good yields. The initially formed E isomer in solution (CDCl3) slowly isomerizes to the Z isomer, indicating greater stability of the latter. The factors affecting the interplay between the 1,5-H shift and GB rearrangement have also been evaluated, and the results are supported by DFT-based computational study.

3D Bioprinted Human Skin Model Recapitulating Native-Like Tissue Maturation and Immunocompetence as an Advanced Platform for Skin Sensitization Assessment.

Physiologically-relevant in vitro skin models hold the utmost importance for efficacy assessments of pharmaceutical and cosmeceutical formulations, offering valuable alternatives to animal testing. Here, an advanced immunocompetent 3D bioprinted human skin model is presented to assess skin sensitization. Initially, a photopolymerizable bioink is formulated using silk fibroin methacrylate, gelatin methacrylate, and photoactivated human platelet releasate. The developed bioink shows desirable physicochemical and rheological attributes for microextrusion bioprinting. The tunable physical and mechanical properties of bioink are modulated through variable photocuring time for optimization. Thereafter, the bioink is utilized to 3D bioprint "sandwich type" skin construct where an artificial basement membrane supports a biomimetic epidermal layer on one side and a printed pre-vascularized dermal layer on the other side within a transwell system. The printed construct is further cultured in the air-liquid interface for maturation. Immunofluorescence staining demonstrated a differentiated keratinocyte layer and dermal extracellular matrix (ECM)-remodeling by fibroblasts and endothelial cells. The biochemical estimations and gene-expression analysis validate the maturation of the printed model. The incorporation of macrophages further enhances the physiological relevance of the model. This model effectively classifies skin irritative and non-irritative substances, thus establishing itself as a suitable pre-clinical screening platform for sensitization tests.

Geminal-dithiol-based precursors for reactive sulfur species.

Caged gem-dithiols have been developed as the donors of reactive sulfur species (RSS), but the chemistry of free gem-dithiols as RSS donors has not been well understood. Herein, we report the study of a free gem-dithiol, 1,3-diphenylpropane-2,2-dithiol, as the precursor for several RSS. It releases H2S under physiological conditions and can be converted to a mono-S-nitrosothiol, which serves as a NO donor. Furthermore, it can be converted to 3,3-dibenzyldithiirane, which is an active sulfur transfer reagent and can induce S-persulfidation.

Plant Peroxisomal Polyamine Oxidase: A Ubiquitous Enzyme Involved in Abiotic Stress Tolerance.

Polyamines (PAs) are positively charged amines that are present in all organisms. In addition to their functions specific to growth and development, they are involved in responding to various biotic and abiotic stress tolerance functions. The appropriate concentration of PA in the cell is maintained by a delicate balance between the catabolism and anabolism of PAs, which is primarily driven by two enzymes, namely diamine oxidase and polyamine oxidase (PAO). PAOs have been found to be localized in multiple subcellular locations, including peroxisomes. This paper presents a holistic account of peroxisomal PAOs. PAOs are flavin adenine dinucleotide-dependent enzymes with varying degrees of substrate specificity. They are expressed differentially upon various abiotic stress conditions, namely heat, cold, salinity, and dehydration. It has also been observed that in a particular species, the various PAO isoforms are expressed differentially with a spatial and temporal distinction. PAOs are targeted to peroxisome via a peroxisomal targeting signal (PTS) type 1. We conducted an extensive bioinformatics analysis of PTS1s present in various peroxisomal PAOs and present a consensus peroxisome targeting signal present in PAOs. Furthermore, we also propose an evolutionary perspective of peroxisomal PAOs. PAOs localized in plant peroxisomes are of potential importance in abiotic stress tolerance since peroxisomes are one of the nodal centers of reactive oxygen species (ROS) homeostasis and an increase in ROS is a major indicator of the plant being in stress conditions; hence, in the future, PAO enzymes could be used as a key candidate for generating abiotic stress tolerant crops.

Association of Single Nucleotide Polymorphism in VDR, GC Globulin and CYP2R1 with the Risk of Esophageal Cancer.

BACKGROUND: The proactive role of vitamin D has been well determined in different cancers. The protein that encodes the components of the vitamin D metabolism could appear to play a pivotal role in vitamin D stability and its maintenance. A polymorphism in vitamin-D-receptor (VDR), carrier globulin/binding protein (GC) and cytochrome P-450 family 2, subfamily R, polypeptide 1 (CYP2R1) genes has been predicted to be associated with the development of cancer. This study was designed to detect the association of VDR, GC Globulin and CYP2R1 gene polymorphism with the risk of esophageal cancer in the North-east Indian population. METHODS: To carry out the study, a total of 100 patients diagnosed with esophageal cancer and 101 healthy controls were enrolled. In a case-control manner, all samples were subjected to do genotype testing for known SNPs on the VDR (rs1544410), GC (rs4588), and CYP2R1 (rs10741657) genes using Restriction-fragment length polymorphism (RFLP) followed by Sanger sequencing. The collected demographic and clinical data were analysed using the statistical software package SPSS v22.0. RESULTS: The VDR haplotype heterozygous TC was found strongly associated with the carcinoma group (OR:1.09, 95%CI:0.67-1.75). The risk factors analysis using the GC globulin rs4588 phenotype, found a positive correlation in terms of mutant AA's harmful influence on the cancer cohort (OR = 1.125, OR=1.125, 95% CI, 0.573-2.206). The influence of the CYP2R1 rs10741657 polymorphism on the malignant cohort revealed that the GG mutant had a significant negative influence on the carcinoma, has an influential role in disease severity ( OR:1.736, at 95% CI; 0.368-8.180). CONCLUSION: In conclusion, this study revealed the potential association of VDR gene polymorphism in the progression and development of esophageal cancer in north east Indian population cohort.