Steric Bulkiness Of Substituents Research Articles

Can Heteroarenes/Arenes Be Hydrogenated Over Catalytic Pd/C Under Ambient Conditions?

Hydrogenation of over a dozen aromatic compounds, including both heteroarenes and arenes, over palladium on carbon (Pd/C, 1–100 mol%) with H2‐balloon pressure at room temperature is reported. Analyses using pyridine as a model substrate revealed that acetic acid was the best solvent, as using only 1 mol% Pd/C provided piperidine quantitatively. Substrate scope analysis and density functional theory calculations indicated that reaction rates are highly dependent on frontier molecular orbital characteristics and the steric bulkiness of substituents. Moreover, the established method was used for the concise synthesis of the anti‐Alzheimer drug donepezil (Aricept®).

NMR analysis of photochromism of bisthiazolylindenols

The photochromic reaction of two derivatives of bisthiazolylindenols was investigated in three solvents of various polarities (C6D12, THF-d8 and CD3CN) by NMR spectroscopy. Photoirradiation can generate two diastereomeric closed forms. High conversion ratio and large diastereomer excess were obtained and the reasons of the excellent properties were discussed in terms of intramolecular hydrogen bonds, steric bulkiness of substituents, and solvent polarities. Two sets of intramolecular nitrogen–hydrogen interactions fix the conformation of the two investigated bisthiazolylindenols in favor of cyclization, which also lead to high diastereoselectivity. The N–H interactions are partially disrupted when polarity of the solvent increases.

QSAR Study on Piperidinecarboxamides as Antiretroviral Agents: An Insight Into the Structural Basis for HIV Coreceptor Antagonist Activity

AbstractChemokines receptors have emerged as important drug targets for the development of agents against the Human Immunodeficiency Virus (HIV)/AIDS pandemic. With the purpose of designing new chemical entities with enhanced antiretroviral potencies, the Quantitative Structure–Activity Relationships (QSAR) study carried out on 122 novel piperidin‐4‐carboxamide derivatives as antagonists of HIV Chemokine Receptor 5 (CCR5) coreceptor binding is presented. The developed model was validated by standard QSAR parameters and through a detailed structural investigation on how it explains and reproduces the quantitative differences observed in the experimentally known activity data. The model showed a good correlative and predictive ability having a cross‐validated correlation coefficient (r2cv) of 0.794 and the conventional correlation coefficient (r2) was found to be 0.830. The study revealed that the CCR5 antagonistic activity exhibited by the series is largely explained by lipophilicity and steric bulkiness of substituents and that substituents with higher lipophilicity and steric superiority are required to make favorable antagonist–CCR5 interaction chemistry. A detailed investigation was made on the structural basis for the antiretroviral activity and the insights gleaned from the study could be usefully employed to design antagonists with a much more enhanced potency and selectivity.

Reactions of Alkenylruthenium(II) Complexes with Hydrosilane: C-Si vs C-H Bond Formation

Abstract Alkenylruthenium complexes, Ru{C(R1)=CH(R2)}Cl(CO)(PPh3)2 (R1 = H, R2 = Ph; R1 = H, R2 = t-Bu; R1 = Ph, R2 = Ph; R1 = CH=CH(SiMe3), R2 = SiMe2Ph), react with HSiMe2Ph via two reaction courses (path A and path B), leading to C–Si and C–H bond formation, respectively. Relative ratio of the two courses is strongly dependent upon steric bulkiness of substituent(s) on the alkenyl ligands.