Synthetic conversion of bryostatin 2 to bryostatin 1 and related bryopyrans

Bryostatin 2 (1a) has been converted to bryostatin 1 (1e) and bryostatin 12 (1i) by a selective protection and deprotection involving the C-26 hydroxyl group. The new bryostatins 1g,1k, and 1m were also prepared starting from bryostatin 2. The C-7 substituents of natural bryostatins 4 and 5 were revised from isovalerate → pivalate employing comparative 1H and 13C NMR studies of the semi-synthetic bryostatins 1k and 1m and the natural products. Key words: bryostatin 2 → 1, selective conversion, bryostatins 4 and 5, pivalates.

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Structural determination of the polysaccharide antigens of Neisseria meningitidis serogroups Y, W-135, and BO

Canadian Journal of Biochemistry ◽

10.1139/o76-001 ◽

1976 ◽

Vol 54 (1) ◽

pp. 1-8 ◽

Cited By ~ 94

Author(s):

Apurba K. Bhattacharjee ◽

Harold J. Jennings ◽

C. Paul Kenny ◽

Adèle Martin ◽

Ian C. P. Smith

Keyword(s):

Sialic Acid ◽

Acetyl Derivative ◽

Major Product ◽

Hydroxyl Group ◽

Nmr Studies ◽

Acetylneuraminic Acid ◽

Nmr Data ◽

Polysaccharide Antigens ◽

C Nmr

The purified high molecular weight serogoup Y meningococcal polysaccharide contains equimolar proportions of D-glucose and N-acetylneuraminic acid and is partially O-acetylated. Carbon-13 nuclear magnetic resonance (NMR) studies, together with other chemical data, have indicated that the polysaccharide is linked only at C-6 of the D-glucose and C-4 of the sialic acid residues, all the linkages being in the α-configuration. The 13C NMR data also indicated that the Y polysaccharide is composed of an alternating sequence of these two different residues, and this was confirmed by its autohydrolysis where the major product was 4-O-α-D-glucopyranosyl-β-D-N-acetylneuraminic acid. The W-135 polysaccharide differs from that of Y only in the absence of O-acetylation and in the configuration of one hydroxyl group of the disaccharide repeating unit. In this case autohydrolysis yielded 4-O-α-D-galactopyranosyl-β-D-N-acetylneuraminic acid as the major product. Structural evidence indicates that the BO and Y polysaccharides are identical.Methanolysis of the Y polysaccharide yielded in addition to the methyl glycosides of glucose and sialic acid, a 9-O-acetyl derivative of the latter. This derivative was formed during the re-N-acetylation process and its formation was mainly due to the presence of sodium ions in the original polysaccharide.

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

Combinatorial Chemistry & High Throughput Screening ◽

10.2174/1386207323666200120112714 ◽

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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Synthesis of Polycycles and Oxacycles by Tandem Metathesis of endo–norbornene Derivatives

Synthesis ◽

10.1055/a-1348-4242 ◽

2021 ◽

Author(s):

Sambasivarao Kotha ◽

Sunil Pulletikurti ◽

Ambareen Fatma ◽

gopal dhangar ◽

gonna somu Naidu

Keyword(s):

Natural Products ◽

Metal Complex ◽

Carbonyl Group ◽

Single Step ◽

Time Dependent ◽

Computational Studies ◽

Nmr Studies ◽

Tricyclic Compounds ◽

One Step ◽

Norbornene Derivatives

Here, we have demonstrated that the presence of a carbonyl group at C7 position is preventing the olefin metathesis of endo-norbornene derivatives due to the complexation of the metal alkylidene. Time-dependent NMR studies showed the presence of new proton signals in the metal alkylidene region, which indicate the formation of metal complex with the carbonyl group of the substrate. These observations were further proved by ESI-MS analysis. Whereas, computational studies provided that the catalyst was interacting with the C7 carbonyl group and aligned perpendicular to that of norbornene olefin. Later, these endo-keto norbornene derivatives were reduced to hydroxyl derivatives diastereoselectively. Ring-rearrangement metathesis (RRM) of these hydroxyl derivatives, produced the [6/5/6], and [5/6/5] carbo-tricyclic cores of the natural products in one step. Whereas the RRM of O-allyl derivatives, delivered the oxa-tricyclic compounds in a single step with excellent yields.

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Structural Investigations of C-Nitrosobenzenes. Part 3.1 Solid-state and Solution 13C NMR Studies, and Crystal Structure of E-(4-CIC6H4NO)2

Journal of Chemical Research ◽

10.1177/174751989902300316 ◽

1999 ◽

Vol 23 (3) ◽

pp. 202-203

Author(s):

Daniel A. Fletcher ◽

Brian G. Gowenlock ◽

Keith G. Orrell ◽

David C. Apperley ◽

Michael B. Hursthouse ◽

...

Keyword(s):

Crystal Structure ◽

Solid State ◽

13C Nmr ◽

Nmr Studies ◽

Structural Investigations ◽

Nmr Data ◽

C Nmr

Solid-state and solution 13C NMR data for the monomers and dimers of 3- and 4-substituted nitrosobenzenes, and the crystal structure of E-(4-CIC6H4NO)2 are reported.

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Structural differences between humic fractions from different soil types as determined by FT-IR and 13 C-NMR studies

The Science of The Total Environment ◽

10.1016/0048-9697(89)90124-1 ◽

1989 ◽

Vol 81-82 ◽

pp. 187-194 ◽

Cited By ~ 23

Author(s):

R. Fründ ◽

H.-D. Lüdemann ◽

F.J. Gonzalez-Vila ◽

G. Almendros ◽

J.C. del Rio ◽

...

Keyword(s):

Soil Types ◽

Nmr Studies ◽

Structural Differences ◽

Ft Ir ◽

Humic Fractions ◽

C Nmr

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Two Dimensional NMR Studies of Marine Natural Products. III.1Reassignment of the13C-NMR Spectrum of Brianthein-X Using Heteronuclear Relayed Coherence Transfer

Spectroscopy Letters ◽

10.1080/00387018608069261 ◽

1986 ◽

Vol 19 (5) ◽

pp. 545-557 ◽

Cited By ~ 4

Author(s):

Gary S. Linz ◽

M. J. Musmar ◽

Alfred J. Weinheimer ◽

Gary E. Martin ◽

James A. Matson

Keyword(s):

Natural Products ◽

Marine Natural Products ◽

Two Dimensional ◽

Coherence Transfer ◽

Nmr Studies ◽

Nmr Spectrum

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Solid state stereochemistry of crown ethers: X-ray crystal structure and 13C NMR studies of the LiNCS complex of 1,4,7,11-tetraoxacyclotetradecane

Canadian Journal of Chemistry ◽

10.1139/v00-008 ◽

2000 ◽

Vol 78 (3) ◽

pp. 316-321

Author(s):

G W Buchanan ◽

A B Driega ◽

G PA Yap

Keyword(s):

Crystal Structure ◽

Solid State ◽

Crown Ether ◽

13C Nmr ◽

Title Complex ◽

Nmr Studies ◽

Nmr Spectrum ◽

X Ray ◽

Large Amplitude Motion ◽

C Nmr

The title complex is asymmetric in the crystal due to the spatial orientation of the NCS function. The space group has been determined to be P21 with a = 9.496(3), b = 8.736(3), c = 9.676(3) Å, β = 117.859(5)°, and Z = 2. The solid state 13C NMR spectrum is consistent with the lack of symmetry in the crystal and there is little evidence for large amplitude motion in the macrocycle as determined from the dipolar dephased spectrum.Key words: macrocyclic crown ether, lithium complex.

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The syntheses of 6-C-alkyl derivatives of methyl α-isomaltoside for a study of the mechanism of hydrolysis by amyloglucosidase

Canadian Journal of Chemistry ◽

10.1139/v01-005 ◽

2001 ◽

Vol 79 (2) ◽

pp. 238-255 ◽

Cited By ~ 4

Author(s):

Ulrike Spohr ◽

Nghia Le ◽

Chang-Chun Ling ◽

Raymond U Lemieux

Keyword(s):

Hydrogen Bonds ◽

Molecular Model ◽

Aromatic Amino Acids ◽

Hydroxyl Group ◽

Bulk Solution ◽

Anomeric Effect ◽

Nmr Studies ◽

Intermolecular Hydrogen Bonds ◽

Model Calculations ◽

Derivatives Of

The epimeric (6aR)- and (6aS)-C-alkyl (methyl, ethyl and isopropyl) derivatives of methyl α-isomaltoside (1) were synthesized in order to examine the effects of introducing alkyl groups of increasing bulk on the rate of catalysis for the hydrolysis of the interunit α-glycosidic bond by the enzyme amyloglucosidase, EC 3.2.1.3, commonly termed glucoamylase (AMG). It was previously established that methyl (6aR)-C-methyl α-isomaltoside is hydrolysed about 2 times faster than methyl α-isomaltoside and about 8 times faster than its S-isomer. The kinetics for the hydrolyses of the ethyl and isopropyl analogs were also recently published. As was expected from molecular model calculations, all the R-epimers are good substrates. A rationale is presented for the catalysis based on conventional mechanistic theories that includes the assistance for the decomposition of the activated complex to products by the presence of a hydrogen bond, which connects the 4a-hydroxyl group to the tryptophane and arginine units. It is proposed that activation of the initially formed complex to the transition state is assisted by the energy released as a result of both of the displacement of perturbed water molecules of hydration at the surfaces of both the polyamphiphilic substrate and the combining site and the establishment of intermolecular hydrogen bonds, i.e., micro-thermodynamics. The dissipation of the heat to the bulk solution is impeded by a shell of aromatic amino acids that surround the combining site. Such shields are known to be located around the combining sites of lectins and carbohydrate specific antibodies and are considered necessary to prevent the disruption of the intermolecular hydrogen bonds, which are of key importance for the stability of the complex. These features together with the exquisite stereoelectronic dispositions of the reacting molecules within the combining site offer a rationalization for the catalysis at ambient temperatures and near neutral pH. The syntheses involved the addition of alkyl Grignard reagents to methyl 6-aldehydo-α-D-glucopyranoside. The addition favoured formation of the S-epimers by over 90%. Useful amounts of the active R-isomers were obtained by epimerization of the chiral centers using conventional methods. Glycosylation of the resulting alcohols under conditions for bromide-ion catalysis, provided methyl (6aS)- and (6aR)-C-alkyl-hepta-O-benzyl-α-isomaltosides. Catalytic hydrogenolysis of the benzyl groups afforded the desired disaccharides. 1H NMR studies established the absolute configurations and provided evidence for conformational preferences.Key words: amyloglucosidase (AMG), exo-anomeric effect, 6-C-alkyl-α-D-glucopyranosides and isomaltosides, mechanism of enzyme catalysis.

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