Chemistry and Biology of Oligovalent β‐(1→2)‐Linked Oligomannosides: New Insights into Carbohydrate‐Based Adjuvants in Immunotherapy

A series of oligovalent carbohydrate assemblies (ranging from mono‐ to pentavalent), derived from three structurally different β‐linked or β‐(1→2)‐linked mannosides, has been chemically synthesized, and the respective compounds have been biologically evaluated in order to investigate their immunostimulatory properties. The Crich methodology for β‐mannosylation was successfully utilized to introduce the β‐linkages, and a click chemistry protocol was utilized to generate the oligovalent derivatives. A convenient protecting group strategy involving the simultaneous use of both p‐methoxybenzyl and benzylidene groups was employed, which allowed a simple and cost‐effective global deprotection step. The immunomodulatory properties of the synthesized multivalent mannosides were evaluated by assessing cytokine production in human white blood cell cultures. The Th2‐type cytokines interleukin‐4 and interleukin‐5 (IL‐4 and IL‐5), the Th1 cytokine interferon‐γ (IFN‐γ), the Treg cytokine IL‐10, and the pro‐inflammatory cytokine tumor necrosis factor (TNF) were included in the screening. A single trivalent acetylated mannobiose derivative was identified as a potent inducer of Treg and Th1 immune response, resulting in strong IL‐10 and moderate IFN‐γ productions dose‐dependently, while inducing no Th2 cytokine response. The immunomodulatory properties of this trivalent mannoside were further studied in vitro in allergen (Bet v)‐stimulated human peripheral blood mononuclear cell cultures of birch pollen allergic subjects. Stimulation with birch pollen induced strong IL‐4 and IL‐5 responses, which could be suppressed by the trivalent acetylated mannobiose derivative. The IL‐10 response was also suppressed, whereas the production of IFN‐γ was strongly enhanced. The results suggest that the identified lead compound has suppressive effects on the Th2‐type allergic inflammatory response and shows potential as a possible lead adjuvant for the specific immunotherapy of allergies.     

Synthesis and biological evaluation of 5′-O-dicarboxylic fatty acyl monoester derivatives of anti-HIV nucleoside reverse transcriptase inhibitors

A number of 5′-O-dicarboxylic fatty acyl monoester derivatives of 3′-azido-3′-deoxythymidine (zidovudine, AZT), 2′,3′-didehydro-2′,3′-dideoxythymidine (stavudine, d4T), and 3′-fluoro-3′-deoxythymidine (alovudine, FLT) were synthesized to improve the lipophilicity and potentially the cellular delivery of parent polar 2′,3′-dideoxynucleoside (ddN) analogs. The compounds were evaluated for their anti-HIV activity. Three different fatty acids with varying chain length of suberic acid (octanedioic acid), sebacic acid (decanedioic acid), and dodecanedioic acid were used for the conjugation with the nucleosides. The compounds were evaluated for anti-HIV activity and cytotoxicity. All dicarboxylic ester conjugates of nucleosides exhibited significantly higher anti-HIV activity than that of the corresponding parent nucleoside analogs. Among all the tested conjugates, 5′-O-suberate derivative of AZT (EC₅₀ = 0.10 nM) was found to be the most potent compound and showed 80-fold higher anti-HIV activity than AZT without any significant toxicity (TC₅₀ >500 nM).     

Solid phase extraction studies on cellulose based chelating resin for separation,pre-concentration and estimation of Cu2+and Ni2+

Chelating resins based on biopolymers, specifically cellulose, offers a green analytical method for determination of metal ions at trace levels present in various samples. It offers a fast, accurate and simple method for separation and pre-concentration of metal ions at low concentrations, prior to their determination by instrumental method. Cellulose based chelating resin (CELL-GLY) has been synthesised by immobilising glycine on it. CELL-GLY was used for the determination of trace amounts of Cu²⁺ and Ni²⁺ from aqueous solutions before their determination by FAAS. The preparation of CELL-GLY involves simple steps, based on natural and easily available biopolymer cellulose, which makes its use as chelating resin is a green method. The Cu²⁺ and Ni²⁺ can be quantitatively recovered from the CELL-GLY in the pH range 4.8–6.9 and 6.9-7.8 respectively with a recovery of more than 95% for each of these metal ions. Recovery of these metal ions using CELL-GLY was quantitative up to 35 °C. The detection limits for copper and nickel by FAAS were 1.20 ppb and 1.40 ppb, respectively. The method was successfully employed for the determination of trace amounts of Cu²⁺ and Ni²⁺ in various samples.     

Atomistic De-novo Inhibitor Generation-Guided Drug Repurposing for SARS-CoV-2 Spike Protein with Free-Energy Validation by Well-Tempered Metadynamics

Computational drug design is increasingly becoming important with new and unforeseen diseases like COVID-19. In this study, we present a new computational de novo drug design and repurposing method and applied it to find plausible drug candidates for the receptor binding domain (RBD) of SARS-CoV-2 (COVID-19). Our study comprises three steps: atom-by-atom generation of new molecules around a receptor, structural similarity mapping to existing approved and investigational drugs, and validation of their binding strengths to the viral spike proteins based on rigorous all-atom, explicit-water well-tempered metadynamics free energy calculations. By choosing the receptor binding domain of the viral spike protein, we showed that some of our new molecules and some of the repurposable drugs have stronger binding to RBD than hACE2. To validate our approach, we also calculated the free energy of hACE2 and RBD, and found it to be in an excellent agreement with experiments. These pool of drugs will allow strategic repurposing against COVID-19 for a particular prevailing conditions.     

Modification of Extended Open Frameworks with Fluorescent Tags for Sensing Explosives: Competition between Size Selectivity and Electron Deficiency

Three new electron‐rich metal–organic frameworks ( MOF‐1 – MOF‐3 ) have been synthesized by employing ligands bearing aromatic tags. The key role of the chosen aromatic tags is to enhance the π‐electron density of the luminescent MOFs. Single‐crystal X‐ray structures have revealed that these MOFs form three‐dimensional porous networks with the aromatic tags projecting inwardly into the pores. These highly luminescent electron‐rich MOFs have been successfully utilized for the detection of explosive nitroaromatic compounds (NACs) on the basis of fluorescence quenching. Although all of the prepared MOFs can serve as sensors for NACs, MOF‐1 and MOF‐2 exhibit superior sensitivity towards 4‐nitrotoluene (4‐NT) and 2,4‐dinitrotoluene (DNT) compared to 2,4,6‐trinitrotoluene (TNT) and 1,3,5‐trinitrobenzene (TNB). MOF‐3 , on the other hand, shows an order of sensitivity in accordance with the electron deficiencies of the substrates. To understand such anomalous behavior, we have thoroughly analyzed both the steady‐state and time‐resolved fluorescence quenching associated with these interactions. Determination of static Stern–Volmer constants (K_S) as well as collisional constants (K_C) has revealed that MOF‐1 and MOF‐2 have higher K_S values with 4‐NT than with TNT, whereas for MOF‐3 the reverse order is observed. This apparently anomalous phenomenon was well corroborated by theoretical calculations. Moreover, recyclability and sensitivity studies have revealed that these MOFs can be reused several times and that their sensitivities towards TNT solution are at the parts per billion (ppb) level.     

Insights into the AIEE of 1,8‐Naphthalimides (NPIs): Inverse Effects of Intermolecular Interactions in Solution and Aggregates

Systematic structural perturbation has been used to fine‐tune and understand the luminescence properties of three new 1,8‐naphthalimides (NPIs) in solution and aggregates. The NPIs show blue emission in the solution state and their fluorescence quantum yields are dependent upon their molecular rigidity. In concentrated solutions of the NPIs, intermolecular interactions were found to quench the fluorescence due to the formation of excimers. In contrast, upon aggregation (in THF / H₂O mixtures), the NPIs show aggregation‐induced emission enhancement (AIEE). The NPIs also show moderately high solid‐state emission quantum yields (ca. 10–12.7 %). The AIEE behaviour of the NPIs depends on their molecular rigidity and the nature of their intermolecular interactions. The NPIs 1 – 3 show different extents of intermolecular (π–π and C?H???O) interactions in their solid‐state crystal structures depending on their substituents. Detailed photophysical, computational and structural investigations suggest that an optimal balance of structural flexibility and intermolecular communication is necessary for achieving AIEE characteristics in these NPIs.     

Fine‐Tuning Dual Emission and Aggregation‐Induced Emission Switching in NPI–BODIPY Dyads

Three new NPI–BODIPY dyads 1 – 3 (NPI=1,8‐naphthalimide, BODIPY=boron‐dipyrromethene) were synthesized, characterized, and studied. The NPI and BODIPY moieties in these dyads are electronically separated by oxoaryl bridges, and the compounds only differ structurally with respect to methyl substituents on the BODIPY fluorophore. The NPI and BODIPY moieties retain their optical features in molecular dyads 1 – 3 . Dyads 1–3 show dual emission in solution originating from the two separate fluorescent units. The variations of the dual emission in these compounds are controlled by the structural flexibilities of the systems. Dyads 1 – 3 , depending on their molecular flexibilities, show considerably different spectral shapes and dissimilar intensity ratios of the two emission bands. The dyads also show significant aggregation‐induced emission switching (AIES) on formation of nano‐aggregates in THF/H₂O with changes in emission color from green to red. Whereas the flexible and aggregation‐prone compound 1 shows AIES, rigid systems with less favorable intermolecular interactions (i.e., 2 and 3 ) show aggregation‐induced quenching of emission. Correlations of the emission intensity and structural flexibility were found to be reversed in solution and aggregated states. Photophysical and structural investigations suggested that intermolecular interactions (e.g., π–π stacking) play a major role in controlling the emission of these compounds in the aggregated state.     

Thiol Modified Chitosan Self-Assembled Monolayer Platform for Nucleic Acid Biosensor

A self-assembled monolayer (SAM) of thiol modified chitosan (SH-CHIT), with thioglycolic acid (TGA) as a modifier to bestow thiol groups, has been prepared onto gold (Au)-coated glass plates for fabrication of the nucleic acid biosensor. The chemical modification of CHIT via TGA has been evidenced by Fourier transform infrared spectroscopy (FT-IR) studies, and the biocompatibility studies reveal that CHIT retains its biocompatible nature after chemical modification. The electrochemical studies conducted onto SH-CHIT/Au electrode reveal that thiol modification in CHIT amino end enhances the electrochemical behavior indicating that it may be attributed to delocalization of electrons in CHIT skeleton that participates in the resonance process. The carboxyl group modified end of DNA probe has been immobilized onto SH-CHIT/Au electrode using N-ethyl-N′-(3-dimethylaminopropyl)carbodimide (EDC) and N-hydroxysuccinimide (NHS) chemistry for detection of complementary, one-base mismatch and non-complementary sequence using electrochemical and optical studies for Mycobacterium tuberculosis detection. It has been found that DNA-SH-CHIT/Au bioelectrode can specifically detect 0.01 μM of target DNA concentration with sensitivity of 1.69?×?10^?6 A μM^?1.     

Phytochemicals as Inhibitors of Bacterial Cell Division Protein FtsZ: Coumarins Are Promising Candidates

Naturally occurring phytochemicals with reported antibacterial activity were screened for their ability to inhibit the bacterial cell division protein Escherichia coli FtsZ. Among the representative compounds, coumarins inhibit the GTPase and polymerization activities of this protein effectively. Further screening with ten coumarin analogs we identified two promising candidates, scopoletin and daphnetin. The former is found to inhibit the GTPase activity of the protein in a noncompetitive manner. Docking of these coumarins with the modeled protein indicate that they bind to T7 loop, which is different from the GTP-binding site (active site), thereby supporting the experimental data. Lowest binding energy is obtained with scopoletin. 3D QSAR indicates the need for groups such as hydroxyl, diethyl, or dimethyl amino in the 7th carbon for enhanced activity. None of the coumarins exhibited cytotoxicity against NIH/3T3 and human embryonic kidney cell lines. The length of Bacillus subtilis increases in the presence of these compounds probably due to the lack of septum formation. Results of this study indicate the role of coumarins in halting the first step of bacterial cell division process.