Synthesis of des-A-B-secocholestanes

1984 ◽  
Vol 62 (6) ◽  
pp. 1081-1084 ◽  
Author(s):  
Wojciech J. Szczepek ◽  
Jacek W. Morzycki ◽  
Zbigniew Bończa-Tomaszewski ◽  
Michał Chodyński ◽  
Władysław J. Rodewald
Keyword(s):  
Hydroxyl Group ◽  
Dioic Acid ◽  
Ruthenium Tetroxide ◽  
Enol Acetate ◽  
Synthetic Routes ◽  
Hydrolysis Of

Two independent synthetic routes to 10-oxo-5, 10-seco-des-A-cholestan-5-oic acid (5) are described. The route including the Baeyer–Villiger rearrangement of (10R)-des-A-cholestan-5-one (2a), followed by hydrolysis of the lactone 3a obtained and oxidation of the C-10 hydroxyl group, seems to be superior to ozonolysis of the 5(10)-enol acetate 6 of des-A-ketone which resulted in the formation of 5,10-seco-des-A-19-norcholestan-5,10-dioic acid (7), in addition to the compound 5. Product 7 and its 6-nor analog 12 have also been obtained by ruthenium tetroxide oxidation of the respective A-ring phenols 8, 9, and 11.

scholarly journals Potential Anti-Acetylcholinesterase Activity of Cassia timorensis DC.

Molecules ◽  
2020 ◽  
Vol 25 (19) ◽  
pp. 4545
Author(s):  
Nurul Amira Nurul Azman ◽  
Maram B. Alhawarri ◽  
Mira Syahfriena Amir Rawa ◽  
Roza Dianita ◽  
Amirah Mohd Gazzali ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
Acetylcholinesterase Activity ◽  
The Other ◽  
Hydroxyl Group ◽  
Anionic Site ◽  
Methanol Extracts ◽  
Plant Parts ◽  
Ache Inhibitory Activity ◽  
First Time ◽  
Hydrolysis Of

Seventeen methanol extracts from different plant parts of five different Cassia species, including C. timorensis, C. grandis, C. fistula, C. spectabilis, and C. alata were screened against acetylcholinesterase (AChE). C. timorensis extracts were found to exhibit the highest inhibition towards AChE whereby the leaf, stem, and flower methanol extracts showed 94–97% inhibition. As far as we are aware, C. timorensis is one of the least explored Cassia spp. for bioactivity. Further fractionation led to the identification of six compounds, isolated for the first time from C. timorensis: 3-methoxyquercetin (1), benzenepropanoic acid (2), 9,12,15-octadecatrienoic acid (3), β-sitosterol (4), stigmasterol (5), and 1-octadecanol (6). Compound 1 showed moderate inhibition towards AChE (IC50: 83.71 μM), while the other compounds exhibited poor to slightly moderate AChE inhibitory activity. Molecular docking revealed that the methoxy substitution of 1 formed a hydrogen bond with TYR121 at the peripheral anionic site (PAS) and the hydroxyl group at C5 formed a covalent hydrogen bond with ASP72. Additionally, the OH group at the C3′ position formed an interaction with the protein at the acyl pocket (PHE288). This possibly explains the activity of 1 in blocking the entry of acetylcholine (ACh, the neurotransmitter), thus impeding the hydrolysis of ACh.

ESTIMATION OF CORTICOSTEROIDS BY THE REDUCTION OF FERRICYANIDE

1959 ◽  
Vol 37 (1) ◽  
pp. 391-398 ◽  
Author(s):  
N. R. Stephenson
Keyword(s):  
Prussian Blue ◽  
Blood Sugar ◽  
Alkaline Medium ◽  
Alkaline Solution ◽  
Reducing Power ◽  
Hydroxyl Group ◽  
Side Chain ◽  
Inhibiting Effect ◽  
Reducing Activity ◽  
Hydrolysis Of

A procedure based on a modification of Folin's micromethod for blood sugar (1, 2) was used to investigate the reducing activity of various corticosteroids. The ferrocyanide produced as a result of the reduction of ferricyanide in alkaline solution was measured photometrically as Prussian blue. With a filter transmitting light at 620 mμ, the relation between the absorbance of the chromogen and the amount of the reducing steroid obeyed Beer's law over the range from 0.005 to 0.050 mg. The oxygen function at C-3 accounted for most of the reducing power of the non-alpha ketolic steroids studied. An oxygen function at C-11 did not affect significantly the reduction of ferricyanide by 17-desoxycorticosteroids. Although the presence of a hydroxyl at C-17 depressed the reducing activity of the alpha-ketol side chain, a fluorine at C-9 and an hydroxyl at C-11 appeared to overcome this inhibiting effect. Evidence was obtained to suggest that a C-16 hydroxyl group was able to increase the reducing action of the alpha-ketolic side chain. Esterification of the C-21 hydroxyl influenced the reduction of ferricyanide only when interference with hydrolysis of the ester in the alkaline medium was experienced.

scholarly journals A Simple Method for the Quantification of Free Isocyanates on the Surface of Cellulose Nanocrystals upon Carbamation using Toluene Diisocyanate

Surfaces ◽  
2019 ◽  
Vol 2 (2) ◽  
pp. 444-454 ◽  
Author(s):  
Hatem Abushammala
Keyword(s):  
Elemental Analysis ◽  
Cellulose Nanocrystals ◽  
Toluene Diisocyanate ◽  
Hydroxyl Group ◽  
Simple Method ◽  
Complete Hydrolysis ◽  
Amine Groups ◽  
Ph Increase ◽  
Hydrolysis Of ◽  
Cellulose Surface

In many reports, cellulose and nanocellulose have been carbamated using 2,4-toluene diisocyanate (2,4-TDI) to allow the grafting of molecules or polymers onto their surfaces. Such a process usually involves the reaction of the more reactive isocyanate group of TDI (para-NCO) selectively with a hydroxyl group from the cellulose surface, followed by the reaction of the free isocyanate (ortho-NCO) with a desired molecule. After the first step, it is not possible, using elemental analysis, to determine the amount of ortho-NCO on the cellulosic surface, as an ideal para/ortho selectivity is difficult to obtain. This paper presents a simple method for the quantification of ortho-NCOs on the surface of cellulose nanocrystals upon TDI-based carbamation. It relies on the pH increase upon a complete hydrolysis of ortho-NCOs to amine groups using acidified dimethylsulfoxide. The method was found to be accurate and valid for a degree of substitution of up to 20%.

The proton affinities and deprotonation enthalpies of β-D-fructopyranose and α-L-sorbopyranose

1991 ◽  
Vol 69 (12) ◽  
pp. 1917-1928 ◽  
Author(s):  
Robert J. Woods ◽  
Walter A. Szarek ◽  
Vedene H. Smith Jr.
Keyword(s):  
Hydrogen Bonding ◽  
Oxygen Atom ◽  
Intramolecular Hydrogen Bonding ◽  
Hydroxyl Group ◽  
Proton Affinities ◽  
Naturally Occurring ◽  
Acid Catalyzed ◽  
Acids And Bases ◽  
Intramolecular Hydrogen ◽  
Hydrolysis Of

The proton affinities (PAs) and deprotonation enthalpies (DPEs) were calculated for the pyranoid forms of two naturally occurring sugars, D-fructose and L-sorbose. In both molecules the PAs of the primary hydroxyl group (HO-1), the anomeric hydroxyl group (HO-2), and the ring-oxygen atom (O-6) were calculated, as were the DPEs of HO-1 and HO-2. The stabilities of the conjugate acids and bases of these sugars are enhanced by the presence of intramolecular hydrogen bonding, a feature that is significant in explaining the differences in sweetness and the rates of mutarotation of the title compounds, as well as the differences in the rates of acid-catalyzed hydrolysis of ketopyranosides. Key words: proton affinity, deprotonation enthalpy, ab initio calculations, AM1, hexuloses.

scholarly journals Regioselective chemo-enzymatic syntheses of ferulate conjugates as chromogenic substrates for feruloyl esterases

2020 ◽  
Author(s):  
Olga Gherbovet ◽  
Fernando Ferreira ◽  
Apolline Clément ◽  
Mélanie Ragon ◽  
Julien Durand ◽  
...  
Keyword(s):  
Aspergillus Niger ◽  
Feruloyl Esterase ◽  
Thermomyces Lanuginosus ◽  
Hydroxyl Group ◽  
Chromogenic Substrates ◽  
Carbohydrate Active Enzymes ◽  
Experimental Application ◽  
Synthetic Routes ◽  
Feruloyl Esterases ◽  
Regioselective Functionalization

Generally, carbohydrate-active enzymes are studied using chromogenic substrates that provide quick and easy color-based detection of enzyme-mediated hydrolysis. In the case of feruloyl esterases, commercially available chromogenic ferulate derivatives are both costly and limited in terms of their experimental application. In this study, we describe solutions for these two issues, using a chemoenzymatic approach to synthesize different ferulate compounds. The overall synthetic routes towards commercially available 5-bromo-4-chloro-3-indolyl and 4-nitrophenyl O-5-feruloyl-α-l-arabinofuranosides 1a and 1b were significantly shortened (7-8 steps reduced to 4-6) and transesterification yields enhanced (from 46 to 73% for 1a and 47 to 86 % for 1b). This was achieved using enzymatic (immobilized Lipolase 100T from Thermomyces lanuginosus) transesterification of unprotected vinyl ferulate to the primary hydroxyl group of α‐l‐arabinofuranosides. Moreover, a novel feruloylated-butanetriol 4-nitrocatechol-1-yl analog 12, containing a cleavable hydroxylated linker was also synthesized in 29% overall yield in 3 steps (convergent synthesis). The latter route combined regioselective functionalization of 4-nitrocatechol and enzymatic transferuloylation. The use of 12 as a substrate to characterize type A feruloyl esterase from Aspergillus niger reveals the advantages of this substrate for the characterizations of feruloyl esterases.

scholarly journals A Direct Silanization Protocol for Dialdehyde Cellulose

Molecules ◽  
2020 ◽  
Vol 25 (10) ◽  
pp. 2458 ◽  
Author(s):  
Arianna Lucia ◽  
Markus Bacher ◽  
Hendrikus W. G. van Herwijnen ◽  
Thomas Rosenau
Keyword(s):  
Aqueous Media ◽  
Hydroxyl Group ◽  
Cross Linking ◽  
Cellulose Derivatives ◽  
Reaction Conditions ◽  
Cellulose Structure ◽  
Dialdehyde Cellulose ◽  
Potential Applications ◽  
The Common ◽  
Hydrolysis Of

Cellulose derivatives have many potential applications in the field of biomaterials and composites, in addition to several ways of modification leading to them. Silanization in aqueous media is one of the most promising routes to create multipurpose and organic–inorganic hybrid materials. Silanization has been widely used for cellulosic and nano-structured celluloses, but was a problem so far if to be applied to the common cellulose derivative “dialdehyde cellulose” (DAC), i.e., highly periodate-oxidized celluloses. In this work, a straightforward silanization protocol for dialdehyde cellulose is proposed, which can be readily modified with (3-aminopropyl)triethoxysilane. After thermal treatment and freeze-drying, the resulting product showed condensation and cross-linking, which was studied with infrared spectroscopy and 13C and 29Si solid-state nuclear magnetic resonance (NMR) spectroscopy. The cross-linking involves both links of the hydroxyl group of the oxidized cellulose with the silanol groups (Si-O-C) and imine-type bonds between the amino group and keto functions of the DAC (-HC=N-). The modification was achieved in aqueous medium under mild reaction conditions. Different treatments cause different levels of hydrolysis of the organosilane compound, which resulted in diverse condensed silica networks in the modified dialdehyde cellulose structure.

scholarly journals A novel 5′-hydroxyl dinucleotide hydrolase activity for the DXO/Rai1 family of enzymes

2019 ◽  
Vol 48 (1) ◽  
pp. 349-358 ◽  
Author(s):  
Selom K Doamekpor ◽  
Agnieszka Gozdek ◽  
Aleksandra Kwasnik ◽  
Joanna Kufel ◽  
Liang Tong
Keyword(s):  
Crystal Structure ◽  
Fission Yeast ◽  
Hydroxyl Group ◽  
Exonuclease Activity ◽  
Rna Turnover ◽  
Rna Modifications ◽  
End Caps ◽  
Group 5 ◽  
Hydrolysis Of ◽  
Insight Into

Abstract Modifications at the 5′-end of RNAs play a pivotal role in determining their fate. In eukaryotes, the DXO/Rai1 family of enzymes removes numerous 5′-end RNA modifications, thereby regulating RNA turnover. Mouse DXO catalyzes the elimination of incomplete 5′-end caps (including pyrophosphate) and the non-canonical NAD+ cap on mRNAs, and possesses distributive 5′-3′ exoribonuclease activity toward 5′-monophosphate (5′-PO4) RNA. Here, we demonstrate that DXO also catalyzes the hydrolysis of RNAs bearing a 5′-hydroxyl group (5′-OH RNA). The crystal structure of DXO in complex with a 5′-OH RNA substrate mimic at 2.0 Å resolution provides elegant insight into the molecular mechanism of this activity. More importantly, the structure predicts that DXO first removes a dinucleotide from 5′-OH RNA. Our nuclease assays confirm this prediction and demonstrate that this 5′-hydroxyl dinucleotide hydrolase (HDH) activity for DXO is higher than the subsequent 5′-3′ exoribonuclease activity for selected substrates. Fission yeast Rai1 also has HDH activity although it does not have 5′-3′ exonuclease activity, and the Rat1-Rai1 complex can completely degrade 5′-OH RNA. An Arabidopsis DXO1 variant is active toward 5′-OH RNA but prefers 5′-PO4 RNA. Collectively, these studies demonstrate the diverse activities of DXO/Rai1 and expands the collection of RNA substrates that can undergo 5′-3′ mediated decay.

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