Transannular participation of the hydroxyl group in the addition of hypobromous acid to some 5-hydroxy-5α-cholest-2-enes

1977 ◽  
Vol 42 (1) ◽  
pp. 353-365 ◽  
Author(s):  
P. Kočovský ◽  
V. Černý
Keyword(s):  
Hydroxyl Group ◽  
Hypobromous Acid

Synthesis of 14-deoxy-14α-strophanthidol

1980 ◽  
Vol 45 (3) ◽  
pp. 921-926 ◽  
Author(s):  
Pavel Kočovský ◽  
Václav Černý
Keyword(s):  
Characteristic Feature ◽  
Title Compound ◽  
Acetoxy Group ◽  
Hydroxyl Group ◽  
Acid Addition ◽  
Hypobromous Acid

A thirteen-step synthesis of 3β,5,19-trihydroxy-5β, 14α-card-20(22)-enolide (I, title compound) from 3β-acetoxy-5-pregnen-20-one (V) is described. A characteristic feature of this approach is the introduction of the 5β-hydroxyl group by hypobromous acid addition to the 5,6-unsaturated-19-acetoxy derivative XV which proceeds with 6(O)π n participation of the acetoxy group (XV(r)XVI(r)XVII).

Neighboring group participation in electrophilic additions: The role of Markovnikov and Fürst-Plattner rule in hypobromous acid addition to 5,6-unsaturated cholestane derivatives

1983 ◽  
Vol 48 (12) ◽  
pp. 3618-3628 ◽  
Author(s):  
Pavel Kočovský
Keyword(s):  
Methyl Ether ◽  
Hydroxyl Group ◽  
Unsaturated Alcohol ◽  
Neighboring Group ◽  
Group Participation ◽  
Acid Addition ◽  
Hypobromous Acid ◽  
Neighboring Group Participation ◽  
Electrophilic Additions

On reaction with hypobromous acid, the unsaturated alcohol IIIa yields the diequatorial bromo epoxide XIX arising from the 5α,6α-bromonium ion XVIIIa on cleavage at C(5) by 19b-hydroxyl group with 6(O)n participation. By contrast, the bromonium ion XVIIIb generated from the unsaturated methyl ether IIIb is cleaved by water as external nucleophile to yield the unstable diaxial bromohydrin XX which undergoes cyclization to the oxirane derivative XXI. A comparison with the reaction course in homologs of the type I and II permits the conclusion that the change in regioselectivity, generally possible outcome of the 5(O)n participation, is only possible for the 6(O)n process if the participating group is a hydroxyl.

Electrophilic additions to 10β-vinyl cholestane derivatives

1983 ◽  
Vol 48 (10) ◽  
pp. 2994-3019 ◽  
Author(s):  
Pavel Kočovský ◽  
Ivo Starý ◽  
František Tureček ◽  
Vladimír Hanuš
Keyword(s):  
Reaction Mechanism ◽  
Double Bond ◽  
Hydroxyl Group ◽  
Acid Addition ◽  
Hypobromous Acid ◽  
Markovnikov Rule ◽  
Vinyl Group ◽  
Electrophilic Additions

Hypobromous acid addition to steroid dienes I-VI proceeds in four steps. The reaction commences by the attack on more reactive endocyclic double bond from the α-side yielding intermediary diaxial bromohydrins XXVIII, XXXIV, XL, XLIV, L and LVI via corresponding α-bromonium ions. The 10β-vinyl group of the bromohydrins then reacts with a second equivalent of the reagent forming transient 19-epimeric bromonium ions. The ions generated from I, II, V and VI are cleaved intramolecularly by the hydroxyl group, in accordance with the Markovnikov rule, giving rise to 19-epimeric dibromo epoxides XXXIa and XXXIIa, XXXVII and XXXVIII, LIIIa and LIVa, LIX and LX. By contrast, the ions generated from III and IV are cleaved in an anti-Markovnikov manner to yield dibromo epoxides XLII, XLVII and XLVIII. Products due to formation of a new C-C bond were not observed. The reaction mechanism and differences in the behaviour of the dienes I-VI are discussed.

Acetoxyl group as control element in electrophilic addition: Participation by acetoxy group and its competition with other participating groups in hypobromous acid addition to some 5-cholestene derivatives

1983 ◽  
Vol 48 (12) ◽  
pp. 3629-3642 ◽  
Author(s):  
Pavel Kočovský
Keyword(s):  
Electrophilic Addition ◽  
Acetoxy Group ◽  
Hydroxyl Group ◽  
Control Element ◽  
Group Participation ◽  
Acid Addition ◽  
Hypobromous Acid ◽  
Contrast Inversion

The 3β-acetoxy cholestene II (with nonparticipating group at the position 19) is known to be attacked with hypobromous acid predominantly from α-site which results in formation of the diaxial bromohydrin XIV. By contrast, inversion of configuration of the 3-acetoxy group leads to a dramatic change in the reaction course: the 3α-acetoxycholestene derivative VIII is preferentially approached by the electrophile from β-site to give the corresponding 5β,6β-bromonium ion XXVII which on cleavage with 6(O)π,n participation by the 3α-acetoxyl yields two products XXIX and XXXI When hydroxy and acetoxy groups can compete in 5(O)n or 6(O)π,n processes, only hydroxyl group participation takes place (IX → XXV and XI → XXXIV). Two acetoxy groups in X compete successfully in 6(O)π,n processes (X → XXXVII + XLI).

Detection method of combustion oscillation characteristics under strong noise background

2020 ◽  
Vol 21 (6) ◽  
pp. 612
Author(s):  
Yunkun Wei ◽  
Tianhong Zhang ◽  
Zhonglin Lin ◽  
Qi Xie ◽  
Yan Zhang
Keyword(s):  
Radiation Thermometry ◽  
Hydroxyl Group ◽  
Interference Signal ◽  
Engine Vibration ◽  
Combustion Technology ◽  
Lean Fuel ◽  
Combustion Oscillation ◽  
Aero Engines ◽  
Temperature Measurement System ◽  
Multispectral Radiation Thermometry

After the lean fuel premixed combustion technology is applied to aero engines, severe combustion oscillations will be cased and led to hidden safety hazards such as engine vibration, further energy waste and other problems. Therefore, it is increasingly important to actively control combustion oscillations. In this paper, a multispectral radiation thermometry (MRT) is used to analyze the hydroxyl group, which is a measurable research object in the combustion chamber of an aero engine, and to fit the functional relationship between the radiation intensity ratio and the temperature in different bands. The theoretical value of the error is <2%. At the same time, in order to solve the problem of weak detection signal and excessive interference signal, an improved frequency domain filtering method based on fast Fourier transform is designed. Besides, the FPGA platform is used to ensure the real-time performance of the temperature measurement system, and simulations and experiments are performed. An oscillating signal with an oscillation frequency of 315 Hz is obtained on the established test platform, and the error is only 1.42%.

α-Glucosidase Inhibition and Docking Studies of 5-Deoxyflavonols and Dihydroflavonols Isolated from Abutilon pakistanicum

2019 ◽  
Vol 23 (17) ◽  
pp. 1857-1866
Author(s):  
Munawar Hussain ◽  
Zaheer Ahmed ◽  
Shamsun N. Khan ◽  
Syed A. A. Shah ◽  
Rizwana Razi ◽  
...  
Keyword(s):  
Methanolic Extract ◽  
Docking Studies ◽  
Hydroxyl Group ◽  
Coumaric Acid ◽  
In Vitro Activity ◽  
Aerial Parts ◽  
First Time ◽  
Acid Esters ◽  
Phenol Moiety

Three new 5-deoxyflavonoid and dihydroflavonoids 2, 3 and 4 have been isolated from the methanolic extract of Abutioln pakistanicum aerial parts, for which structures were elucidated explicitly by extensive MS- and NMR-experiments. In addition to these, 3,7,4′-trihydroxy-3′-methoxy flavonol (1) is reported for the first time from Abutioln pakistanicum. Compound 2 and 4 are p-coumaric acid esters while compounds 2–4 exhibited α-glucosidase inhibitory activity. Docking studies indicated that the ability of flavonoids 2, 3 and 4 to form multiple hydrogen bonds with catalytically important residues is decisive hence is responsible for the inhibition activity. The docking results signified the observed in-vitro activity quite well which is in accordance with previously obtained conclusion that phenol moiety and hydroxyl group are critical for the inhibition of α-glucosidase enzyme.

Combinatorial Synthesis of Novel 9R-Acyloxyquinine Derivatives as Insecticidal Agents

2020 ◽  
Vol 23 (2) ◽  
pp. 111-118
Author(s):  
Zhiping Che ◽  
Jinming Yang ◽  
Di Sun ◽  
Yuee Tian ◽  
Shengming Liu ◽  
...  
Keyword(s):  
Natural Products ◽  
Double Bond ◽  
Insecticidal Activity ◽  
Structural Modification ◽  
Combinatorial Synthesis ◽  
Hydroxyl Group ◽  
Botanical Insecticide ◽  
Mythimna Separata ◽  
Lead Compounds

Background: It is one of the effective ways for pesticide innovation to develop new insecticides from natural products as lead compounds. Quinine, the main alkaloid in the bark of cinchona tree as well as in plants in the same genus, is recognized as a safe and potent botanical insecticide to many insects. The structural modification of quinine into 9R-acyloxyquinine derivatives is a potential approach for the development of novel insecticides, which showed more toxicity than quinine. However, there are no reports on the insecticidal activity of 9Racyloxyquinine derivatives to control Mythimna separata. Methods: Endeavor to discover biorational natural products-based insecticides, 20 novel 9Racyloxyquinine derivatives were prepared and assessed for their insecticidal activity against M. separata in vivo by the leaf-dipping method at 1 mg/mL. Results: Among all the compounds, especially derivatives 5i, 5k and 5t exhibited the best insecticidal activity with final mortality rates of 50.0%, 57.1%, and 53.6%, respectively. Conclusion: Overall, a free 9-hydroxyl group is not a prerequisite for insecticidal activity and C9- substitution is well tolerated; modification of out-ring double-bond is acceptable, and hydrogenation of double-bond enhances insecticidal activity; Quinine ring is essential and open of it is not acceptable. These preliminary results will pave the way for further modification of quinine in the development of potential new insecticides.

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