Mursaleem Ansari

Deoxyglycosides represent an important class of bioactive molecules with broad medicinal significance. In this study, 1,3-annulated-2-deoxyglycosides were synthesized from glycals via a Lewis acid-mediated domino sequence. Unlike the classical Ferrier glycosylation, this work highlights the role of glycals in annulation reactions. Protected glycals such as acetylated d-galactal, d-arabinal, and l-fucal underwent highly regioselective glycosylation with external nucleophiles, affording 1,3-annulated-2-deoxyglycosides as the sole products. In contrast, glycals such as d-glucal, l-rhamnal, and d-xylal either failed to deliver the desired products under the same conditions or furnished them in lower yields. The substrate scope for 1,3-annulated-2-deoxyglycosides includes diverse protected glycals and acceptors, including 1-naphthols, 2-naphthols, phenols, and thionaphthalenes. Mechanistic investigations, supported by DFT calculations, revealed that the ortho positions of aromatic phenols preferentially attack the thermodynamically favorable C-3 position of the oxocarbenium ion rather than the anomeric center. These computational insights align with experimental observations, as a key reaction intermediate was isolated and characterized.

This study reports that the well-known Co(III) precursor Co(η⁵-Cp*)I₂(CO) (1) is an effective precatalyst for dehydrocoupling reactions of phosphines. Reaction monitoring by NMR, complemented by ESI-MS and EPR, suggests that Co(III) complexes containing secondary and primary phosphine ligands play an important role in this catalysis but that redox chemistry is also facile for these complexes, resulting in paramagnetic species. Representative examples of the mono(phosphine) complexes Co(η⁵-Cp*)I₂(PR₂H) (2) and Co(η⁵-Cp*)I₂(PRH₂) (4) and bis(phosphine) complexes [Co(η⁵-Cp*)I(PR₂H)₂] I (3) have been prepared. The characterization of these complexes through structural, computational, spectroscopic, and electrochemical analysis is reported and serves as a foundation for considering their mechanistic significance in the observed catalytic dehydrocoupling chemistry.

Structural and spectroscopic investigations of compound II in ascorbate peroxidase (APX) have yielded conflicting conclusions regarding the protonation state of the crucial Fe(IV) intermediate. Neutron diffraction and crystallographic data support an iron(IV)-hydroxo formulation, whereas Mössbauer, X-ray absorption (XAS), and nuclear resonance vibrational spectroscopy (NRVS) studies appear consistent with an iron(IV)-oxo species. Here we examine APX with spectroscopy-oriented QM/MM calculations and extensive exploration of the conformational space for both possible formulations of compound II. We establish that irrespective of variations in the orientation of a vicinal arginine residue and potential reorganization of proximal water molecules and hydrogen bonding, the Fe–O distances for the oxo and hydroxo forms consistently fall within distinct, narrow, and nonoverlapping ranges. The accuracy of geometric parameters is validated by coupled-cluster calculations with the domain-based local pair natural orbital approach, DLPNO-CCSD(T). QM/MM calculations of spectroscopic properties are conducted for all structural variants, encompassing Mössbauer, optical, X-ray absorption, and X-ray emission spectroscopies and NRVS. All spectroscopic observations can be assigned uniquely to an Fe(IV)═O form. A terminal hydroxy group cannot be reconciled with the spectroscopic data. Under no conditions can the Fe(IV)═O distance be sufficiently elongated to approach the crystallographically reported Fe–O distance. The latter is consistent only with a hydroxo species, either Fe(IV) or Fe(III). Our findings strongly support the Fe(IV)═O formulation of APX-II and highlight unresolved discrepancies in the nature of samples used across different experimental studies.