Thiazetidin-2-ylidenes as four membered N-heterocyclic carbenes: theoretical studies and the generation of complexes with N+ center

(Imidazol-2-ylidene) → S coordination interactions and its modulation upon S-oxidation

(NHC) → E coordination interactions are being explored in many chemical species, including carbones and nitreones. (NHC) → S interactions are rare, but increasing attention is being paid to the compounds containing such interactions. The electron deficiency at the S centre is responsible for triggering electron donation from the NHC unit in (NHC) → SR(+) systems. It is well known that the positive charge at the sulfur centre increases upon single oxidation and further increases upon double oxidation. This implies that (NHC) → S interactions may become explicit after S-oxidation in the (NHC) → SR(+) systems. To explore this hypothesis, we performed quantum chemical design and synthesis of (NHC) → SR(+), (NHC) → S(O)R(+), and (NHC) → S(O)2R(+) complexes in which the ligands are imidazol-2-ylidene derivatives. Eight derivatives of the (imidazol-2-ylidene) → SR(+) systems were generated, and their sulfoxide and sulfone derivatives were obtained by oxidation using urea-H2O2 and mCPBA, respectively. The crystal structures of three compounds belonging to a series were determined. A comparison of the geometric, energetic and electronic characteristics confirmed the hypothesis that the (NHC) → S coordination interaction becomes comparatively stronger with an increase in oxygen atoms at the sulfur centre.

L→S Coordination Complexes Containing Benzothiazol-2-ylidene Ligand: Quantum Chemical Analysis and Synthesis

(NHC)→E coordination interactions were known where NHC is an N-heterocyclic carbene, and E is a main group element (B, C, N, Si, P). Recently, it was suggested that compounds with (NHC)→S coordination chemistry are also possible. This work reports quantum chemical analysis and synthesis of (NHC)→S-R(+) complexes in which benzothiazol-2-ylidene acts as a ligand. A Density functional study established that (NHC)→S interaction can best be described as a coordination interaction. Synthetic efforts were made, initially, to generate divalent sulfur compounds containing benzothiazole substituents. N-alkylation of the heterocyclic ring in these sulfides using methyl triflate led to the generation of the desired products with (NHC)→S coordination chemistry, which involves the in situ generation of NHC ring ligands. The observed changes in the 13C NMR spectra, before and after methylation, confirmed the change in the electronic character of the C-S bond from a covalent character to a coordination character.

Identification of CYP3A4 inhibitors as potential anti-cancer agents using pharmacoinformatics approach

Biguanide derivatives exhibit a wide variety of therapeutic applications, including anti-cancer effects. Metformin is an effective anti-cancer agent against breast cancer, lung cancer, and prostate cancer. In the crystal structure (PDB ID: 5G5J), it was found that metformin is found in the active site of CYP3A4, and the associated anti-cancer effect was explored. Taking clues from this work, pharmacoinformatics research has been carried out on a series of known and virtual biguanide, guanylthiourea (GTU), and nitreone derivatives. This exercise led to the identification of more than 100 species that exhibit greater binding affinity toward CYP3A4 in comparison to that of metformin. Selected six molecules were subjected to molecular dynamics simulations, and the results are presented in this work.

The importance of four-membered NHCs in stabilizing Breslow intermediates on benzoin condensation pathway

N-heterocyclic carbenes (NHCs) have been established to be effective organocatalysts for facilitating the benzoin condensation and many other reactions. These reactions involve the formation of a Breslow intermediate (BI), which exhibits umpolung chemistry. To facilitate organocatalysis, several new cyclic carbenes are being introduced, four-membered NHCs are of special interest. Whether these NHCs can exhibit catalytic influence or not, can be evaluated by exploring the potential energy surface (PES) of the benzoin condensation reaction. Quantum chemical analysis has been carried out to compare the PES of these four-membered NHCs with that of standard five-membered NHCs to explore their catalytic ability. The barrier for the first step of the reaction for the formation of BI is comparable in all the cases. But the barrier for the second step of the reaction leading to the benzoin formation from BI is estimated to be very high for the four membered NHCs. These results indicate that the probability of identifying and isolating the BI is very high in comparison to the completion of benzoin condensation reaction in the case of the four-membered NHCs.

A cyclic divalent N(I) species isoelectronic to carbodiphosphoranes

The formation of a rare type of diphosphazenium cation is described. Its synthesis features a unique oxidative dealkylation of an iminophosphorane-phosphole by a silver(I) salt. DFT study of this compound reveals the low valent character of the N(I) center.