DABCO-catalyzed esterification of N-pivaloyl-activated amides.

A previously elusive organocatalytic protocol for the esterification of amides is disclosed. DABCO (10 mol%) is identified as an effective catalyst for the esterification of N-pivaloyl amides. Although N-pivaloyl amides are nearly planar (amide bond twist (τ) = 4.54° and pyramidalization (χN = 6.39°)) and resonance stabilized, esterification is achieved with high efficiency. The developed protocol is generic, phenols, thiophenols, aliphatic alcohols, and thiols were identified as effective substrates. Furthermore, the reaction features a broad substrate scope and excellent functional group tolerance. To exemplify the practical applicability of the developed protocol, the esterification of bioactive natural products, pterostilbene and menthol, is demonstrated. In addition, a series of competitive experiments were conducted to establish the reactivity pattern of alcohols, thiols, and phenols, which could serve as selectivity principles for future synthetic design. Our findings signify a notable advancement in utilizing amides as versatile synthetic building blocks in organic synthesis under metal-free conditions.

Polydiacetylene/lipid-coated red-emissive silica nanorods for the sustained release and ameliorated anticancer efficacy of a Ru(arene) complex bearing piperlongumine natural product.

A suitable drug delivery strategy for metallodrugs is as significant as the strategies adopted for an efficient metallodrug design. In this study, piperlongumine, which is isolated from long pepper, is coordinated with a Ru(II)-p-cymene moiety to obtain an organoruthenated complex containing the natural product (Ru(pip)). The isolated complex shows higher cytotoxicity in MCF-7 breast cancer cells than in THP-1 leukemia and HepG2 liver cancer cells. The IC50 value of the complex in non-cancerous HEK-239 cells is also almost equal to that in MCF-7 cells. Next, with an aim to modulate the antiproliferative activity of Ru(pip) using a drug delivery strategy, the complex is loaded into mesoporous silica nanorods (MSNRs), which have a higher surface area than spherical silica nanoparticles. Furthermore, the outer surface of the loaded nanorods is covered with a polydiacetylene-lipid (PL) hybrid bilayer. Given the unique optical properties of polydiacetylene, the PL coating modifies non-fluorescent MSNRs into red-emissive particles (PL-Ru(pip)@MSNRs), which can be useful for diagnostic applications. The release profile studies reveal that the ene-yne conjugation in the PL coating ensures the sustained release of the complex from nanoparticles in both physiological and simulated cancer cell media. While Ru(pip) exhibits both necrotic and apoptotic modes of cell death, PL-Ru(pip)@MSNRs preferably induce the apoptotic mode of cell death in MCF-7 and THP-1 cells. Also, the nanoformulation exhibits a higher percentage of cell cycle arrest in the G0/G1 phase than Ru(pip), as measured by flow cytometry analysis. In contrast, the in vitro antioxidant potency of the complex is decreased after being loaded into PL-coated silica nanoparticles.

A concise synthesis route to access bioactive natural products-dihydrocurcumins/1,7-diarylheptanoids.

Dihydrocurcumin (DHCUR), a natural product and reductive metabolite of curcumin (CUR), is limitedly explored owing to its low bioavailability and limited accessibility due to lack of straightforward synthetic routes and poor yields with known methods. Herein, we report a concise and straightforward route to synthesize DHCUR and its analogs in excellent yields. Dihydroferuloylacetone is condensed with aldehydes to obtain desired DHCURs/1,7-diarylheptanoids in 81-90% yields. The developed protocol facilitates easy access to bioactive natural products, 1,7-diarylheptanoids and DHCUR, for therapeutic study.

In Vitro and In Vivo Therapeutic Potential of 6,6'-Dihydroxythiobinupharidine (DTBN) from Nuphar lutea on Cells and K18-hACE2 Mice Infected with SARS-CoV-2.

We have previously published research on the anti-viral properties of an alkaloid mixture extracted from Nuphar lutea, the major components of the partially purified mixture found by NMR analysis. These are mostly dimeric sesquiterpene thioalkaloids called thiobinupharidines and thiobinuphlutidines against the negative strand RNA measles virus (MV). We have previously reported that this extract inhibits the MV as well as its ability to downregulate several MV proteins in persistently MV-infected cells, especially the P (phospho)-protein. Based on our observation that the Nuphar extract is effective in vitro against the MV, and the immediate need that the coronavirus disease 2019 (COVID-19) pandemic created, we tested here the ability of 6,6'-dihydroxythiobinupharidine DTBN, an active small molecule, isolated from the Nuphar lutea extract, on COVID-19. As shown here, DTBN effectively inhibits SARS-CoV-2 production in Vero E6 cells at non-cytotoxic concentrations. The short-term daily administration of DTBN to infected mice delayed the occurrence of severe clinical outcomes, lowered virus levels in the lungs and improved survival with minimal changes in lung histology. The viral load on lungs was significantly reduced in the treated mice. DTBN is a pleiotropic small molecule with multiple targets. Its anti-inflammatory properties affect a variety of pathogens including SARS-CoV-2 as shown here. Its activity appears to target both pathogen specific (as suggested by docking analysis) as well as cellular proteins, such as NF-κB, PKCs, cathepsins and topoisomerase 2, that we have previously identified in our work. Thus, this combined double action of virus inhibition and anti-inflammatory activity may enhance the overall effectivity of DTBN. The promising results from this proof-of-concept in vitro and in vivo preclinical study should encourage future studies to optimize the use of DTBN and/or its molecular derivatives against this and other related viruses.

Amidic resonance not a barrier for transamidation of N-pivaloyl activated amides: catalyst, base and additive free conditions.

Transamidation of twistless (twist angle (τ) = 4.54°) and resonance stabilized N-pivaloyl activated amides is demonstrated in the absence of a catalyst, base and additive. Furthermore, C-N (1.374 Å) and CO (1.222 Å) bond lengths indicate the existence of amidic resonance; yet, transamidation is achieved at room temperature with alkyl amines in a short reaction time (0.5-2 h) with 60-97% yield. Amines bearing protic hydroxy and carboxylic acid groups were tolerated under the reaction conditions. Thus, our findings imply that N-pivaloyl-activated planar and resonance-stabilized amides are sufficiently reactive for nucleophilic addition.

Inhibition of Cysteine Proteases by 6,6'-Dihydroxythiobinupharidine (DTBN) from Nuphar lutea.

The specificity of inhibition by 6,6'-dihydroxythiobinupharidine (DTBN) on cysteine proteases was demonstrated in this work. There were differences in the extent of inhibition, reflecting active site structural-steric and biochemical differences. Cathepsin S (IC50 = 3.2 µM) was most sensitive to inhibition by DTBN compared to Cathepsin B, L and papain (IC50 = 1359.4, 13.2 and 70.4 µM respectively). DTBN is inactive for the inhibition of Mpro of SARS-CoV-2. Docking simulations suggested a mechanism of interaction that was further supported by the biochemical results. In the docking results, it was shown that the cysteine sulphur of Cathepsin S, L and B was in close proximity to the DTBN thiaspirane ring, potentially forming the necessary conditions for a nucleophilic attack to form a disulfide bond. Covalent docking and molecular dynamic simulations were performed to validate disulfide bond formation and to determine the stability of Cathepsins-DTBN complexes, respectively. The lack of reactivity of DTBN against SARS-CoV-2 Mpro was attributed to a mismatch of the binding conformation of DTBN to the catalytic binding site of Mpro. Thus, gradations in reactivity among the tested Cathepsins may be conducive for a mechanism-based search for derivatives of nupharidine against COVID-19. This could be an alternative strategy to the large-scale screening of electrophilic inhibitors.

6,6'-Dihydroxythiobinupharidine (DTBN) Purified from Nuphar lutea Leaves Is an Inhibitor of Protein Kinase C Catalytic Activity.

Water lily (Nuphar) bioactive extracts have been widely used in traditional medicine owing to their multiple applications against human ailments. Phyto-active Nuphar extracts and their purified and synthetic derivatives have attracted the attention of ethnobotanists and biochemists. Here, we report that 6,6'-dihydroxythiobinupharidine (DTBN), purified from extracts of Nuphar lutea (L.) Sm. leaves, is an effective inhibitor of the kinase activity of members of the protein kinase C (PKC) family using in vitro and in silico approaches. We demonstrate that members of the conventional subfamily of PKCs, PKCα and PKCγ, were more sensitive to DTBN inhibition as compared to novel or atypical PKCs. Molecular docking analysis demonstrated the interaction of DTBN, with the kinase domain of PKCs depicting the best affinity towards conventional PKCs, in accordance with our in vitro kinase activity data. The current study reveals novel targets for DTBN activity, functioning as an inhibitor for PKCs kinase activity. Thus, this and other data indicate that DTBN modulates key cellular signal transduction pathways relevant to disease biology, including cancer.

Programmed photodegradation of polymeric/oligomeric materials derived from renewable bioresources.

Renewable polymeric materials derived from biomass with built-in phototriggers were synthesized and evaluated for degradation under irradiation of UV light. Complete decomposition of the polymeric materials was observed with recovery of the monomer that was used to resynthesize the polymers.