Aza-Michael addition of 1,2-diazoles to structurally diverse enones: Efficient methods toward β-amino ketones

An efficient and mild protocol was realized using 1,2-diazoles and related heterocycles with cyclic and acyclic enones in presence of T3P (2,4,6-tripropyl-1,3,5,2,4,6-trioxatriphosphorinane-2,4,6-trioxide) toward the regioselective formation of N-cycloalkyl heterocycles at room temperature. The developed reaction conditions showcased good selectivity over a wide range of 1,2-diazoles and enones by delivering N-cycloalkyl heterocycles in excellent yields.     

Intramolecular Proton Transfer in 2‐(2′‐hydroxyphenyl)oxazolo[4,5‐b]pyridine: Evidence for Tautomer in the Ground State

The intramolecular proton transfer in a newly synthesized molecule, 2‐(2′‐hydroxyphenyl)oxazolo[4,5‐b]pyridine (HPOP) is studied using UV‐visible absorption, fluorescence emission, fluorescence excitation and time‐resolved fluorescence spectroscopy. In the ground state, the molecule exists as cis‐ and trans‐enol in all the solvents. However, in dioxane, alcohols, acetonitrile, dimethylformamide and dimethylsulfoxide the keto tautomer is also observed in the ground state. Dual fluorescence is observed in HPOP where the large Stoke shifted emission is due to emission from the excited‐state intramolecular proton transfer product, whereas the other emission is the normal emission from enol form. The fluorescence (both normal and tautomer emission) of HPOP is less than those of corresponding benzoxazole and imidazopyridine derivatives. This reveals that the nonradiative decay becomes more efficient upon substitution of electronegative atom on the charge acceptor group. The pH studies substantiate the conclusion that (unlike in its imidazole analog) the third ground state species is the keto tautomer and not the monoanion. The effect of temperature on cis‐enol‐trans‐enol‐keto equilibrium and the nonradiative deactivation from the excited state are also investigated.     

Generalized hybrid derivative coupling model for finite nuclei

The generalized hybrid derivative coupling model has been applied to explore various ground state properties of different nuclei. In this work we have confined our calculation only to the model characterized by the hybridization parameter α = 1/4 which gives better results than the other models of the same class, as we have seen earlier, for nuclear matter calculations. The binding energy, single-particle energy spectra, density and charge radii of different doubly closed nuclei like ¹⁶O, ⁴⁰Ca, ⁴⁸Ca, ⁹⁰Zr, ¹³²Sn, ²⁰⁸Pb have been studied. The success of this model, in describing the doubly closed nuclei, motivates us to extend this calculation further in the case of open shell nuclei after incorporating the pairing interaction and using a BCS transformation. We have calculated the binding energy for such nuclei. We have also studied the isotopic shift for different Pb isotopes with respect to ²⁰⁸Pb. We have compared our results with the other standard theoretical results as well as with the experimental values. Received: 18 August 2000 / Accepted: 13 April 2001     

Overview on Recent Approaches towards Synthesis of 2‐Keto‐annulated Oxazole Derivatives

In recent years, oxazole derivatives have emerged as one of the formidable groups of compounds in the field of medicinal chemistry and drug discovery. The titled compounds 2‐keto‐annulated oxazoles play an important role towards the medicinal aspects. There has been an appearance of a significant number of research articles and reviews to explore the wide utility of oxazole derivatives. However, till now, there has been no dedicated review published focusing on the synthesis of 2‐keto‐annulated oxazole derivatives. Herein, we have presented the recent protocols available in literature for the synthesis of 2‐keto‐annulated oxazoles and highlighted the advantages of these methods that would attract the attention of a broad range of readers in the chemistry community.     

Double C-H activation: the palladium-catalyzed direct C-arylation of xanthines with arenes

The novel Pd-catalyzed C(sp(2))-H/C(sp(2))-H cross-coupling of unactivated xanthines with unactivated arenes utilizing a combination of Ag(I) and O(2) as oxidants exclusively yields C-8 arylated xanthines in a single synthetic operation.     

Porcine dentin sialoprotein glycosylation and glycosaminoglycan attachments

Background  

Dentin sialophosphoprotein (Dspp) is a multidomain, secreted protein that is critical for the formation of tooth dentin. Mutations in DSPP cause inherited dentin defects categorized as dentin dysplasia type II and dentinogenesis imperfecta type II and type III. Dentin sialoprotein (Dsp), the N-terminal domain of dentin sialophosphoprotein (Dspp), is a highly glycosylated proteoglycan, but little is known about the number, character, and attachment sites of its carbohydrate moieties.