scholarly journals Antiprotozoal dimeric naphthylisoquinolines, mbandakamines B3 and B4, and related 5,8′-coupled monomeric alkaloids, ikelacongolines A–D, from a Congolese Ancistrocladus liana

RSC Advances ◽  
2019 ◽  
Vol 9 (21) ◽  
pp. 12034-12046 ◽  
Author(s):  
Jean-Pierre Mufusama ◽  
Doris Feineis ◽  
Virima Mudogo ◽  
Marcel Kaiser ◽  
Reto Brun ◽  
...  
Keyword(s):  
Steric Hindrance ◽  
Naphthylisoquinoline Alkaloids

The discovery of the two unsymmetrically coupled dimeric naphthylisoquinoline alkaloids, the mbandakamines B3 and B4, showing a high steric hindrance at the central biaryl axis and displaying pronounced antiplasmodial activities, is described.

scholarly journals Ancistrotectoquinones A and B, the First Quinoid Naphthylisoquinoline Alkaloids, from the Chinese Liana Ancistrocladus tectorius

2016 ◽  
Vol 11 (7) ◽  
pp. 1934578X1601100
Author(s):  
Gerhard Bringmann ◽  
Minjuan Xu ◽  
Raina Seupel ◽  
Doris Feineis ◽  
Jun Wu
Keyword(s):  
Dft Calculations ◽  
Steric Hindrance ◽  
Time Dependent ◽  
Free Energies ◽  
Biomimetic Oxidation ◽  
Naphthylisoquinoline Alkaloids ◽  
The Absolute ◽  
Diastereomeric Purity

From the leaves and stems of Ancistrocladus tectorius (Ancistrocladaceae) from the Chinese island Hainan, two novel-type 7,3′-coupled naphthylisoquinolines, named ancistrotectoquinones A (4) and B (5), were isolated. They are the first alkaloids with a 1,4-naphthoquinone portion coupled to an isoquinoline moiety. Due to the lowered degree of steric hindrance next to the biaryl axis and for electronic reasons, 4 and 5 occur as pairs of configurationally semi-stable, and, thus slowly interconverting atropo-diastereomers. The Gibbs free energies of activation between the two atropisomers of ancistrotectoquinone A (4a/b) were determined by measuring the time-dependent decrease of diastereomeric purity of freshly separated samples enriched with the M- or P-atropisomer and, computationally, by DFT calculations. The absolute configurations at the biaryl axes of the atropo-diastereomers of 4a/b and 5a/b were assigned by online LC-CD analysis. The stereostructure of 4a/b was further confirmed by its semi-synthesis from the likewise 7,3′-coupled ‘normal' naphthylisoquinoline alkaloid ancistrotectorine (6), by biomimetic oxidation with Fremy's salt.

Steric hindrance influence of a diazo link upon mesogenic properties of some ligands and related copper complexes

1997 ◽  
Vol 94 ◽  
pp. 1695-1714 ◽  
Author(s):  
P Lesot ◽  
F Perez ◽  
P Judeinstein ◽  
JP Bayle ◽  
H Allouchi ◽  
...  
Keyword(s):  
Steric Hindrance ◽  
Copper Complexes

METABOLISM OF 17α-HYDROXYPROGESTERONE-4-14C-17α-CAPROATE BY HOMOGENATES OF RAT LIVER AND HUMAN PLACENTA

1961 ◽  
Vol 36 (4) ◽  
pp. 511-519 ◽  
Author(s):  
Margaret Wiener ◽  
Charles I. Lupa ◽  
E. Jürgen Plotz
Keyword(s):  
Rat Liver ◽  
Human Placenta ◽  
Steric Hindrance ◽  
Placental Tissue ◽  
Caproic Acid ◽  
Major Product ◽  
Side Chain ◽  
Anaerobic Conditions ◽  
Prolonged Action ◽  
Long Acting

ABSTRACT 17α-hydroxyprogesterone-4-14C-17α-caproate (HPC), a long-acting progestational agent, was incubated with homogenates of rat liver and human placenta. The rat liver was found to reduce Ring A of HPC under anaerobic conditions to form allopregnane-3β,17α-diol-20-one-17α-caproate and pregnane-3β,17α-diol-20-one-17α-caproate, the allopregnane isomer being the major product. The caproic acid ester was neither removed nor altered during the incubation. Placental tissue did not attack HPC under conditions where the 20-ketone of progesterone was reduced. It is postulated that this absence of attack on the side chain is due to steric hindrance from the caproate ester, and that this may account for the prolonged action of HPC.

Tyrosine-Selective Bioconjugation with Iminoxyl Radicals

2020 ◽  
Author(s):  
Katsuya Maruyama ◽  
Takashi Ishiyama ◽  
Yohei Seki ◽  
Kounosuke Oisaki ◽  
Motomu Kanai
Keyword(s):  
Reaction Time ◽  
Steric Hindrance ◽  
Room Temperature ◽  
Water Soluble ◽  
Light Irradiation ◽  
Sodium Ascorbate ◽  
Iminoxyl Radical ◽  
Short Reaction Time ◽  
Modified Peptides ◽  
The Stability

A novel Tyr-selective protein bioconjugation using the water-soluble persistent iminoxyl radical is described. The conjugation proceeded with high Tyr-selectivity and short reaction time under biocompatible conditions (room temperature in buffered media under air). The stability of the conjugates was tunable depending on the steric hindrance of iminoxyl. The presence of sodium ascorbate and/or light irradiation promoted traceless deconjugation, restoring the native Tyr structure. The method is applied to the synthesis of a protein-dye conjugate and further derivatization to azobenzene-modified peptides.

Synthesis of Conjugated Triynes via Alkyne Metathesis

2019 ◽  
Author(s):  
Idriss Curbet ◽  
Sophie Colombel-Rouen ◽  
Romane Manguin ◽  
Anthony Clermont ◽  
Alexandre Quelhas ◽  
...  
Keyword(s):  
Steric Hindrance ◽  
High Selectivity ◽  
Alkyne Metathesis ◽  
Cross Metathesis ◽  
Synthetic Strategy ◽  
Sterically Hindered ◽  
Site Selective

<div> <div> <div> <div> <p>The synthesis of conjugated triynes by molybdenum-catalyzed alkyne metathesis is reported. Strategic to the success of this approach is the utilization of sterically-hindered diynes that allowed for the site- selective alkyne metathesis to produce the desired con- jugated triyne products. The steric hindrance of alkyne moiety was found to be crucial in preventing the for- mation of diyne byproducts. This novel synthetic strategy was amenable to self- and cross-metathesis providing straightforward access to the corresponding symmetrical and dissymmetrical triynes with high selectivity. </p> </div> </div> </div> </div>

Regioselectivity of nucleophilic aromatic photosubstitution in the biphenyl series. Photohydrolysis of some dimethoxynitrobiphenyls

1987 ◽  
Vol 52 (10) ◽  
pp. 2482-2491 ◽  
Author(s):  
Ján Urban ◽  
Petr Kuzmič ◽  
David Šaman ◽  
Milan Souček
Keyword(s):  
Nitro Group ◽  
Steric Hindrance ◽  
The Other ◽  
Quantum Yields ◽  
Hydroxide Anion ◽  
Tert Butanol ◽  
Nitro Derivatives

Anaerobic photolysis of dimethoxynitrobiphenyls IIIa-VIa in aqueous alkaline tert-butanol gave products of nucleophilic photosubstitution of methoxyl by hydroxide anion, while the dimethoxybiphenyls Ia and IIa were found unreactive. Regioselectivity of the reaction was examined in view of a possible “extended meta activation” by the nitro group. The most reactive substrate IIIa gives both C-3 and C-4 substitution products with an unsubstantial preference for the latter, which opposes the “extended meta selectivity” rule. All of the other compounds obey the rule, and 3,4-dimethoxy-3'-nitrobiphenyl (IVa) even displayed absolute selectivity by yielding C-3 substituted compound as the only product. 2,5-Dimethoxy substituted compounds underwent photosubstitution which much lower quantum yields than their 3,4-substituted counterparts, most probably due to some steric hindrance of conjugation. Similarly, 3-nitro-substituted biphenyls exhibited much lower overall reactivity than 4-nitro derivatives.

scholarly journals The structure of SeviL, a GM1b/asialo-GM1 binding R-type lectin from the mussel Mytilisepta virgata

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Kenichi Kamata ◽  
Kenji Mizutani ◽  
Katsuya Takahashi ◽  
Roberta Marchetti ◽  
Alba Silipo ◽  
...  
Keyword(s):  
Immune System ◽  
Sialic Acid ◽  
Ligand Binding ◽  
Steric Hindrance ◽  
Sequence Similarity ◽  
Binding Assays ◽  
Subunit Interface ◽  
Nmr Techniques ◽  
And Control ◽  
Asialo Gm1

AbstractSeviL is a recently isolated lectin found to bind to the linear saccharides of the ganglioside GM1b (Neu5Ac$$\alpha$$ α (2-3)Gal$$\beta$$ β (1-3)GalNAc$$\beta$$ β (1-4)Gal$$\beta$$ β (1-4)Glc) and its precursor, asialo-GM1 (Gal$$\beta$$ β (1-3)GalNAc$$\beta$$ β (1-4)Gal$$\beta$$ β (1-4)Glc). The crystal structures of recombinant SeviL have been determined in the presence and absence of ligand. The protein belongs to the $$\beta$$ β -trefoil family, but shows only weak sequence similarity to known structures. SeviL forms a dimer in solution, with one binding site per subunit, close to the subunit interface. Molecular details of glycan recognition by SeviL in solution were analysed by ligand- and protein-based NMR techniques as well as ligand binding assays. SeviL shows no interaction with GM1 due to steric hindrance with the sialic acid branch that is absent from GM1b. This unusual specificity makes SeviL of great interest for the detection and control of certain cancer cells, and cells of the immune system, that display asialo-GM1.

Electronic and steric impact of bis-NHC ligands on reactions of Pt3S2 cores in trinuclear complexes bearing bis-NHC ligands with various lengths of alkylene bridges

2021 ◽  
Vol 50 (35) ◽  
pp. 12079-12082
Author(s):  
Natsuki Yabune ◽  
Hiroshi Nakajima ◽  
Takanori Nishioka
Keyword(s):  
Steric Hindrance ◽  
Trinuclear Complexes

A silver(i) ion attacks the sulfide ligand of a triplatinum complex bearing ethylene-bridged bis-NHC ligands to afford a heptanuclear complex with two Ag–S bonds due to the steric hindrance of the ligands covering the Pt–Pt bonds.

Nanoparticle-based fluorescence probe for detection of NF-κB transcription factor in single cell via steric hindrance

2021 ◽  
Vol 188 (7) ◽  
Author(s):  
Yuedi Ding ◽  
Zhenqiang Fan ◽  
Bo Yao ◽  
Dong Xu ◽  
Minhao Xie ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Single Cell ◽  
Steric Hindrance ◽  
Fluorescence Probe

Effects of steric hindrance and electron density of ester prodrugs on controlling the metabolic activation by human carboxylesterase

2021 ◽  
pp. 100391
Author(s):  
Masato Takahashi ◽  
Ibuki Hirota ◽  
Tomoyuki Nakano ◽  
Tomoyuki Kotani ◽  
Daisuke Takani ◽  
...  
Keyword(s):  
Electron Density ◽  
Steric Hindrance ◽  
Metabolic Activation ◽  
Ester Prodrugs
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