androstane skeleton with a keto-enol tautomerism at the cyclopentane ring. Wecarried out further isolation for PFTase inhibitors from the cultured broth of strain FO-3929 and found andrastin D (4, Fig. 1). In this paper, fermentation, isolation, structure elucidation, and biological properties of 4 are described. A stock culture of strain FO-3929 was inoculated into six 500-ml Erlenmeyer flasks...

Biologically and pharmaceutically active core structures containing a new class of 4-hydroxy-α-carbolines, dihydropyrido[2,3-b]indoles, pyrimido[4,5-b] and [5,4-b]indoles have been synthesized in good yields via Pd-catalyzed amidation and cyclizations. The keto-enol tautomerism in 4-hydroxy-α-carbolines has been investigated by DFT calculations and spectroscopic techniques. The fluorescence stu...

In this laboratory exercise we will measure the Equilibrium Constant Kc for the keto-enol tautomerism of two -diketones and two -diketoesters. This will be accomplished by measuring the signal strength of key protons in the Nuclear Magnetic Resonance (NMR) spectrum of the equilibrium system. The influence of the solvent on the equilibrium position will be examined by considering the measured ...

Because carbonyl groups can participate in both hydrogen bonds and n→π* interactions, these two interactions likely affect one another. Herein, enhancement of an amidic n→π* interaction is shown to reduce the ability of β-keto amides to tautomerize to the enol, indicating decreased hydrogen-bonding capacity of the amide carbonyl group. Thus, an n→π* interaction can have a significant effect on ...

zoanthamine-type alkaloids display a wide spectrum of biological effects. this study aimed to examine the inhibitory effects of norzoanthamine and its ten homologues of zoanthamine class on human fibroblast collagenase by modeling a three-dimensional structure of the ligands at collagenase using energy minimization, docking, molecular dynamics simulation and mm-pb/gbsa binding free energy calcu...

Pulse Radiolysis, OH Radicals, Acetylacetone, Reaction Mechanisms Pulse radiolysis experiments monitoring optical absorbance as well as conductivity and in-situ ESR radiolysis studies show that the OH radical reacts with the enol (k = 8.6 x 109 M_1 s_1) and the enolate (k = 7.4 X 109 M_1 s-1) forms of acetylacetone by addition to the C = C double bond in aqueous N2O saturated solution. The OH r...

The title bis-piperidine, C26H28N2O3, was unexpectedly obtained via a dimerization mechanism promoted by acetic acid when performing the Dieckmann cyclization of a chiral amido ester. The S,S configuration was assigned by reference to the enanti-omerically pure starting material. In the mol-ecule, two core heterocycles are linked by a σ bond. One ring includes a keto-enol group, while the other...

Recent studies have shed light on the energy dissipation mechanism of oxybenzone, a common ingredient in commercial sunscreens. After UVA photoexcitation, the dissipation mechanism may be understood in terms of an initial ultrafast excited state enol → keto tautomerisation, followed by nonadiabatic transfer to the ground electronic state and subsequent collisional relaxation to the starting eno...

O estudo do tautomerismo ceto-enólico e da estereoquímica de uma benzofenona natural com propriedades inibitórias sobre HIV, denominada (1R,5R,7R,8S)-(+)-3-(10-(3,4diidroxifenil)-10-hidroximetileno)-8-metil-1,5,7-tris(3-metil-2-butenil)-8-(4-metil-3-pentenil)biciclo[3.3.1]nonano-2,4,9-triona (a), a qual foi isolada das sementes de Garcinia brasiliensis, é apresentado. A estrutura cristalina de ...

Photoexcitation with blue light of the flavin chromophore in BLUF photoreceptors induces a switch into a metastable signaling state that is characterized by a red-shifted absorption maximum. The red shift is due to a rearrangement in the hydrogen bond pattern around Gln63 located in the immediate proximity of the isoalloxazine ring system of the chromophore. There is a long-lasting controversy ...