Controlled diastereoselection in 2-lithio-1,3-dithiane additions onto α-substituted γ-lactols. Model studies toward bryostatins from (R)-pantolactone

1991 ◽  
Vol 69 (1) ◽  
pp. 62-69 ◽  
Author(s):  
René Roy ◽  
Allan W. Rey
Keyword(s):  
Key Words ◽  
Absolute Configuration ◽  
Nucleophilic Addition ◽  
Major Product ◽  
Model Studies ◽  
Nuclear Overhauser Enhancement ◽  
The Absolute ◽  
Nuclear Overhauser ◽  
Very High

Homochiral α-substituted γ-lactols 3 and 4 derived from (R)-pantolactone 1 were used in 2-lithio-1,3-dithiane additions to afford very high controls in diastereoselectivities arising from 1,2-asymmetric inductions. Thus non-chelation controlled nucleophilic addition on 3 gave the anti diastereomer 5 as the major product (92% de), while the chelation controlled addition on 4 furnished the syn diastereomer 7 (96% de) as the almost exclusive product. The stereochemical outcomes of these reactions were proven unambiguously by locking the conformation of the syn- and anti-triol adducts 7 and 8 through their respective acetonides and by nuclear Overhauser enhancement measurements. The lack of 1,3-dioxolane formation in the case of the anti-triol 8 was taken as a further confirmation of the absolute configuration at the newly created stereocenter. Key words: byrostatin, pantolactone, α-hydroxylactol, dithiane.

A facile synthesis of methyl 3,6-dideoxy-α-L-xylo-hexopyranoside (colitose)

1978 ◽  
Vol 56 (20) ◽  
pp. 2686-2690 ◽  
Author(s):  
David R. Bundle ◽  
Staffan Josephson
Keyword(s):  
Nmr Spectroscopy ◽  
Absolute Configuration ◽  
Catalytic Hydrogenation ◽  
Major Product ◽  
Facile Synthesis ◽  
The Absolute

Methyl 3,6-dideoxy-α-L-xylo-hexopyranoside (7) bas been synthesised in four steps from methyl α-L-fucopyranoside. The intermediate methyl 3,4-O-benzylidene-α-L-fucopyranoside was separated into the S (1a) and R (1b) diastereoisomers and the absolute configuration established by proton and carbon-13 nmr spectroscopy. Under the conditions of the Hanessian–Hullar reaction methyl 4-O-benzoyl-3-bromo-3,6-dideoxy-α-L-gulopyranoside was the major product. Each diastereoisomer 1a or 1b gave identical products and product ratios; the stereochemistry and relative proportions of these products were determined by proton and carbon-13 nmr. The synthesis of ascarylose from methyl α-L-rhamnopyranoside by an analogous route is also reported. The bromo deoxy intermediates were reduced to the dideoxy sugars by catalytic hydrogenation with palladium.

scholarly journals Synthesis and HPLC-ECD Study of Cytostatic Condensed O,N-Heterocycles Obtained from 3-Aminoflavanones

Biomolecules ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 1462
Author(s):  
Ádám Szappanos ◽  
Attila Mándi ◽  
Katalin Gulácsi ◽  
Erika Lisztes ◽  
Balázs István Tóth ◽  
...  
Keyword(s):  
Cell Lines ◽  
Absolute Configuration ◽  
Major Product ◽  
Acid Ceramidase ◽  
Substitution Pattern ◽  
Aryl Group ◽  
Ic50 Values ◽  
The Absolute ◽  
Cis And Trans ◽  
Condensed Heterocycles

Racemic chiral O,N-heterocycles containing 2-arylchroman or 2-aryl-2H-chromene subunit condensed with morpholine, thiazole, or pyrrole moieties at the C-3-C-4 bond were synthesized with various substitution patterns of the aryl group by the cyclization of cis- or trans-3-aminoflavanone analogues. The 3-aminoflavanone precursors were obtained in a Neber rearrangement of oxime tosylates of flavanones, which provided the trans diastereomer as the major product and enabled the isolation of both the cis- and trans-diastereomers. The cis- and trans-aminoflavanones were utilized to prepare three diastereomers of 5-aryl-chromeno[4,3-b][1,4]oxazines. Antiproliferative activity of the condensed heterocycles and precursors was evaluated against A2780 and WM35 cancer cell lines. For a 3-(N-chloroacetylamino)-flavan-4-ol derivative, showing structural analogy with acyclic acid ceramidase inhibitors, 0.15 μM, 3.50 μM, and 6.06 μM IC50 values were measured against A2780, WM35, and HaCat cell lines, and apoptotic mechanism was confirmed. Low micromolar IC50 values down to 2.14 μM were identified for the thiazole- and pyrrole-condensed 2H-chromene derivatives. Enantiomers of the condensed heterocycles were separated by HPLC using chiral stationary phase, HPLC-ECD spectra were recorded and TDDFT-ECD calculations were performed to determine the absolute configuration and solution conformation. Characteristic ECD transitions of the separated enantiomers were correlated with the absolute configuration and effect of substitution pattern on the HPLC elution order was determined.

Controlled oxidations of benzo[a]pyrene

1986 ◽  
Vol 64 (7) ◽  
pp. 1247-1253 ◽  
Author(s):  
E. Lee-Ruff ◽  
H. Kazarians-Moghaddam ◽  
M. Katz
Keyword(s):  
Singlet Oxygen ◽  
High Field ◽  
Chemical Shifts ◽  
Product Distribution ◽  
Major Product ◽  
Nuclear Overhauser Enhancement ◽  
Nuclear Overhauser ◽  
Singlet Oxygen Reaction ◽  
Proton Chemical Shifts ◽  
Oxygen Reaction

The four diones derived from benzo[a]pyrene oxidation have been characterized by high-field nuclear magnetic resonance techniques including 2-D COSY and selective nuclear Overhauser enhancement. All the proton chemical shifts for these four quinones have been uneqivocally assigned. The direct photoxidation of benzo[a]pyrene gives a product distribution very similar to the TPP photosensitized oxygenation, suggesting singlet oxygen is involved in the former. A major product, which was characterized as the 6-seco derivative 6 and not previously reported, was detected in the singlet oxygen reaction. The presence of this product suggests a possible mechanism for quinone formation in the singlet oxygen reaction. One-electron oxidations of benzo[a]pyrene were carried out using tris(p-bromophenyl)aminium hexachloroantimonate and quenching of the radical cation with superoxide or water. The product distribution in this case was quite different from that obtained in the direct photooxidation.

The structure and partial synthesis of imbricatine, a benzyltetrahydroisoquinoline alkaloid from the starfish Dermasterias imbricata

1991 ◽  
Vol 69 (1) ◽  
pp. 20-27 ◽  
Author(s):  
David L. Burgoyne ◽  
Shichang Miao ◽  
Charles Pathirana ◽  
Raymond J. Andersen ◽  
William A. Ayer ◽  
...  
Keyword(s):  
Key Words ◽  
Absolute Configuration ◽  
Spectroscopic Analysis ◽  
Chemical Degradation ◽  
Model Compounds ◽  
Partial Synthesis ◽  
The Absolute

The structure of imbricatine (1), a cytotoxic metabolite of the starfish Dermasterias imbricata, has been determined by spectroscopic analysis and chemical degradation. Synthesis of model compounds 7 and 18 provided evidence for the absolute configuration and constitution of the benzyltetrahydroisoquinoline substructure of imbricatine. Key words: imbricatine, asteroid, alkaloid.

DETERMINATION OF THE ABSOLUTE CONFIGURATION OF NEW PIPERIDIN-4-ONE DERIVATIVE FROM Pellacalyx saccardianus BY NOESY SPECTROSCOPY

2016 ◽  
Vol 78 (3-2) ◽  
Author(s):  
Salam Ahmed Abed ◽  
Hasnah Mohd Sirat
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Nmr Spectroscopy ◽  
Magnetic Resonance ◽  
Absolute Configuration ◽  
X Ray ◽  
X Ray Crystallography ◽  
The Absolute ◽  
Nuclear Overhauser ◽  
Nuclear Magnetic

A new alkaloid, pellacalyxin was isolated from the leaves of Pellacalyx saccardianus of Rhizophoraceae family. Pellacalyxin was analyzed using nuclear Overhauser spectroscopy (NOESY) nuclear magnetic resonance (NMR) technique to determine the absolute configuration. The analysis of absolute configuration of pellacalyxin was supported by X-ray crystallography. 1H-1H NOESY NMR spectroscopy exhibited that pellacalyxin possesses two chiral centers (3S) and (6R).

Evaluation of Different Synthetic Routes to (2R,3R)-3-Hydroxymethyl-2-(4-hydroxy- 3-methoxyphenyl)-1,4-Benzodioxane-6-Carbaldehyde

2020 ◽  
Vol 23 (26) ◽  
pp. 2960-2968
Author(s):  
Renáta Kertiné Ferenczi ◽  
Tünde-Zita Illyés ◽  
Sándor Balázs Király ◽  
Gyula Hoffka ◽  
László Szilágyi ◽  
...  
Keyword(s):  
Absolute Configuration ◽  
Stereoselective Synthesis ◽  
Cotton Effect ◽  
Enantioselective Synthesis ◽  
Aryl Group ◽  
Target Molecule ◽  
Synthetic Routes ◽  
The Absolute

The reported enantioselective synthesis for the preparation of (+)-(2R,3R)-2-(4- hydroxy-3-methoxyphenyl)-3-hydroxymethyl-1,4-benzodioxane-6-carbaldehyde, precursor for the stereoselective synthesis of bioactive flavanolignans, could not be reproduced. Thus, the target molecule was prepared via the synthesis and separation of diastereomeric O-glucosides. TDDFT-ECD calculations and the 1,4-benzodioxane helicity rule were utilized to determine the absolute configuration. ECD calculations also confirmed that the 1Lb Cotton effect is governed by the helicity of the heteroring, while the higher-energy ECD transitions reflect mainly the orientation of the equatorial C-2 aryl group.

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