A Biomimetic Synthesis-Enabled Stereochemical Assignment of Rhodotomentones A and B, Two Unusual Caryophyllene-Derived Meroterpenoids from Rhodomyrtus tomentosa

2021 ◽  
Author(s):  
Lu-Ming Deng ◽  
Li-Jun Hu ◽  
Wei Tang ◽  
Jia-Xin Liu ◽  
Xiao-Jun Huang ◽  
...  
Keyword(s):  
Ring System ◽  
Biomimetic Synthesis ◽  
Stereochemical Assignment ◽  
Rhodomyrtus Tomentosa

Rhodotomentones A and B (1 and 2), two unusual caryophyllene-derived meroterpenoids (CDMTs) featuring a rare 6/6/9/4/6/6 hexacyclic ring system, along with their biogenetically-related CDMTs 7 and 12–15, were isolated from...

scholarly journals A Biomimetic Synthetic Approach to the Frondosins

2016 ◽  
Vol 69 (12) ◽  
pp. 1420 ◽  
Author(s):  
Kevin K. W. Kuan ◽  
Aylin M. C. Hirschvogel ◽  
Jonathan H. George
Keyword(s):  
Marine Sponge ◽  
Ring Expansion ◽  
Cascade Reaction ◽  
Ring System ◽  
Biomimetic Synthesis ◽  
Synthetic Approach ◽  
Compelling Evidence

The frondosins are a family of five marine sponge-derived meroterpenoids. We propose that the 6–7 ring system common to each of the frondosins is biosynthesized via ring expansion of a 6–6 ring system. Compelling evidence in favour of this proposal was obtained in the form of a biomimetic synthesis of the frondosin 6–7 ring system, which features a highly stereo- and regio-selective ring expansion cascade reaction as the key step.

Stochasting modeling of planetary ring systems

1984 ◽  
Vol 75 ◽  
pp. 461-469 ◽  
Author(s):  
Robert W. Hart
Keyword(s):  
Maximum Entropy ◽  
Ring System ◽  
The Sun ◽  
Ultimate State ◽  
Interparticle Interactions ◽  
Ring Systems ◽  
First Order ◽  
Planetary Ring ◽  
Insight Into

ABSTRACTThis paper models maximum entropy configurations of idealized gravitational ring systems. Such configurations are of interest because systems generally evolve toward an ultimate state of maximum randomness. For simplicity, attention is confined to ultimate states for which interparticle interactions are no longer of first order importance. The planets, in their orbits about the sun, are one example of such a ring system. The extent to which the present approximation yields insight into ring systems such as Saturn's is explored briefly.

Effectiveness of Brushing Associated with Oral Irrigation in Maintenance of Peri-Implant Tissues and Overdentures: Clinical Parameters and Patient Satisfaction.

2020 ◽  
Author(s):  
Marcela Moreira Salles ◽  
Viviane de Cássia Oliveira ◽  
Ana Paula Macedo ◽  
Claudia Helena Silva-Lovato ◽  
Helena de Freitas Oliveira Paranhos
Keyword(s):  
Patient Satisfaction ◽  
Analogue Scale ◽  
Ring System ◽  
Complete Dentures ◽  
Gingival Index ◽  
Prosthetic Rehabilitation ◽  
Mean Values ◽  
Probing Depth ◽  
Significant Difference ◽  
High Level

Implant-supported prostheses hygiene and peri-implant tissues health are considered to be predictive factors for successful prosthetic rehabilitation. Therefore, the purpose of this study was to evaluate the effectiveness of brushing associated with oral irrigation measured as biofilm-removing capacity, maintenance of healthy oral tissues, and patient satisfaction. A randomized, crossover clinical trial was conducted with 38 patients who wore conventional maxillary complete dentures and mandibular overdentures retained by the O-ring system. The patients were instructed to use the following hygiene methods for 14 days: mechanical brushing [MB (brush and dentifrice - Control)]; and MB with oral irrigation [WP (Waterpik - Experimental)]. Biofilm-removing capacity and maintenance of healthy oral tissues were evaluated by the Modified Plaque Index (PI), Gingival Index (GI), Probing Depth (PD), and Bleeding on Probing Index (BP) recorded at baseline and after each method. In parallel, patients answered a specific questionnaire using a Visual Analogue Scale after each hygiene method. Data were analyzed by Friedman and Wilcoxon tests (α=0.05). The results showed significantly lower PI, GI, PD, and BP indices after application of the hygiene methods (P<0.001) than those observed at baseline. However, no significant difference was found between MB and WP. The satisfaction questionnaire responses to both methods showed high mean values for all questions, with no statistically significant difference found between the answers given after the use of MB and WP (P>0.05). The findings suggest that WP was effective in reducing PI, GI, PD, and BP indices and provided a high level of patient satisfaction.

Synthesis of Spongidine A, D and Petrosaspongiolide L Methyl Ester Using Pyridine C-H Functionalization

2019 ◽  
Author(s):  
Florian Bartels ◽  
Manuela Weber ◽  
Mathias Christmann
Keyword(s):  
Natural Products ◽  
Methyl Ester ◽  
Hydrogen Atom ◽  
Phospholipase A2 ◽  
Late Stage ◽  
Hydrogen Atom Transfer ◽  
Ring System ◽  
Tetracyclic Core ◽  
Intramolecular Hydrogen ◽  
Phospholipase A2 Inhibitors

<div>An efficient strategy for the synthesis of the potent phospholipase A2 inhibitors spongidine A and D is presented. The tetracyclic core of the natural products was assembled via an intramolecular hydrogen atom transfer‐initiated Minisci reaction. A divergent late‐stage functionalization of the tetracyclic ring system was also used to achieve a concise synthesis of petrosaspongiolide L methyl ester.</div>

Tele-Substitution Reactions in the Synthesis of a Promising Class of Antimalarials

2020 ◽  
Author(s):  
Marat Korsik ◽  
Edwin Tse ◽  
David Smith ◽  
William Lewis ◽  
Peter J. Rutledge ◽  
...  
Keyword(s):  
Heterocyclic Ring ◽  
Ring System ◽  
Substitution Reactions ◽  
Laboratory Notebook ◽  
Polar Solvents ◽  
X Ray ◽  
X Ray Crystallography ◽  
The Core ◽  
Nmr Data

<p></p><p>We have discovered and studied a <i>tele</i>substitution reaction in a biologically important heterocyclic ring system. Conditions that favour the <i>tele</i>-substitution pathway were identified: the use of increased equivalents of the nucleophile or decreased equivalents of base, or the use of softer nucleophiles, less polar solvents and larger halogens on the electrophile. Using results from X-ray crystallography and isotope labelling experiments a mechanism for this unusual transformation is proposed. We focused on this triazolopyrazine as it is the core structure of the <i>in vivo </i>active anti-plasmodium compounds of Series 4 of the Open Source Malaria consortium.</p> <p> </p> <p>Archive of the electronic laboratory notebook with the description of all conducted experiments and raw NMR data could be accessed via following link <a href="https://ses.library.usyd.edu.au/handle/2123/21890">https://ses.library.usyd.edu.au/handle/2123/21890</a> . For navigation between entries of laboratory notebook please use file "Strings for compounds in the article.pdf" that works as a reference between article codes and notebook codes, also this file contain SMILES for these compounds. </p><br><p></p>

Synthesis and Reactivity of Precolibactin 886

2019 ◽  
Author(s):  
Seth Herzon ◽  
Alan R. Healy ◽  
kevin wernke ◽  
Chung Sub Kim ◽  
Nicholas Lees ◽  
...  
Keyword(s):  
Colorectal Cancer ◽  
Gene Cluster ◽  
Amino Alcohol ◽  
Biomimetic Synthesis ◽  
Cross Linking ◽  
E Coli ◽  
Hplc Purification ◽  
Structural Assignment ◽  
Biosynthetic Precursor ◽  
Double Oxidation

<div>The clb gene cluster encodes the biosynthesis of metabolites known as precolibactins and colibactins. The clb pathway is found in gut commensal E. coli, and clb metabolites are thought to initiate colorectal cancer via DNA cross-linking. Precolibactin 886 (1) is one of the most complex isolated clb metabolites; it contains a 15-atom macrocycle and an unusual 5-hydroxy-3-oxazoline ring. Here we report confirmation of the structural assignment via a biomimetic synthesis of precolibactin 886 (1) proceeding through the amino alcohol 9. Double oxidation of 9 afforded the unstable α-ketoimine 2 which underwent macrocyclization to precolibactin 886 (1) upon HPLC purification (3% from 9). Studies of the putative precolibactin 886 (1) biosynthetic precursor 2, the model α-ketoimine 25, and the α-dicarbonyl 26 revealed that these compounds are susceptible to nucleophilic rupture of the C36–C37 bond. Moreover, cleavage of 2 produces other known clb metabolites or biosynthetic intermediates. This unexpected reactivity explains the difficulties in isolating full clb metabolites and accounts for the structure of a recently identified colibactin–adenine adduct. The colibactin peptidase ClbP deacylates synthetic precolibactin 886 (1) to form a non-genotoxic pyridone, suggesting precolibactin 886 (1) lies off-path of the major biosynthetic route.</div>

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