ABSTRACT
Inspired by crystal structures, we designed and achieved a catalyst-free Michael reaction for the preparation of an N1-alkyl pyrazole in a high yield (>90%) with excellent regioselectivity (N1/N2 > 99.9:1). The scope of this protocol has been extended to accomplish the first general regioselective N1-alkylation of 1H-pyrazoles to give di-, tri-, and tetra-substituted pyrazoles in a single step. The resulting pyrazoles bear versatile functional groups such as bromo, ester, nitro, and nitrile, offering opportunities for late-stage functionalization. This efficient methodology will have an impact on drug discovery, as several Food and Drug Administration-approved drugs are pyrazole derivatives. A working hypothesis for the regioselectivity is proposed. X-ray crystal structures of the products that highlight the attractive interactions are discussed. This report provides a rare source for the further elucidation of the attractive interactions because the isomeric ratios and the crystal structures are directly related.
Subject(s)
Pyrazoles , Alkylation , Catalysis , Isomerism , Pyrazoles/chemistryABSTRACT
The potassium affinities of Na,K-ATPase isozymes are important determinants of their physiological roles in skeletal muscle. This study measured the apparent K⺠and Rb⺠affinities of the Na,K-ATPase α1 and α2 isozymes in intact, dissociated myofibers obtained from WT and genetically altered mice (α1S/Sα2R/R and skα2-/-). It also validates a new method to quantify cations in intact, dissociated myofibers, using inductively coupled plasma mass spectrometry (ICP-MS). Our findings were that: (1) The extracellular substrate sites of Na,K-ATPase bind Rb⺠and K⺠with comparable apparent affinities; however; turnover rate is reduced when Rb⺠is the transported ion; (2) The rate of Rb⺠uptake by the Na,K-ATPase is not constant but declines with a half-time of approximately 1.5 min; (3) The apparent K⺠affinity of the α2 isozymes for K⺠is significantly lower than α1. When measured in intact fibers of WT and α1S/Sα2R/R mice in the presence of 10 µM ouabain; the K1/2,K of α1 and α2 isozymes are 1.3 and 4 mM, respectively. Collectively, these results validate the single fiber model for studies of Na,K-ATPase transport and kinetic constants, and they imply the existence of mechanisms that dynamically limit pump activity during periods of active transport.
Subject(s)
Isoenzymes/metabolism , Potassium/metabolism , Rubidium/metabolism , Sodium-Potassium-Exchanging ATPase/metabolism , Animals , Biological Transport , Kinetics , Male , Mass Spectrometry , Mice , Mice, Inbred C57BL , Muscle, Skeletal/metabolism , Sodium/metabolismABSTRACT
A systematic study of the N-substitution reactions of 3-substituted pyrazoles under basic conditions has been undertaken. Regioselective N1-alkylation, -arylation, and -heteroarylation of 3-substituted pyrazoles have been achieved using K2CO3-DMSO. The regioselectivity is justified by the DFT calculations at the B3LYP/6-31G**(d) level. A consistent steric effect on chemical shift has been observed for N-alkyl pyrazole analogues. Twenty-five X-ray crystallographic structures have been obtained to confirm the regiochemistry of the major products.