scholarly journals Unexpected Racemization in the Course of the Acetalization of (+)-(S)-5-Methyl-Wieland–Miescher Ketone with 1,2-Ethanediol and TsOH under Classical Experimental Conditions

2019 ◽  
Vol 20 (24) ◽  
pp. 6147
Author(s):  
Francesca Leonelli ◽  
Irene Piergentili ◽  
Giulio Lucarelli ◽  
Luisa Maria Migneco ◽  
Rinaldo Marini Bettolo
Keyword(s):  
Natural Products ◽  
Experimental Conditions ◽  
Enantiomerically Pure ◽  
Bioactive Natural Products ◽  
Classical Procedure ◽  
Enantioselective Syntheses

(+)-(S) and (−)-(R)-5-methyl-Wieland-Miescher ketone (+)-1 and (−)-1, are important synthons in the diastereo and enantioselective syntheses of biological and/or pharmacological interesting compounds. A key step in these syntheses is the chemoselective C(1)O acetalization to (+)-5 and (−)-5, respectively. Various procedures for this transformation have been described in the literature. Among them, the classical procedure based on the use of 1,2-ethanediol and TsOH in refluxing benzene in the presence of a Dean-Stark apparatus. Within our work on bioactive natural products, it occurred to us to observe the partial racemization of (+)-5 in the course of the acetalization of (+)-1 by means of the latter methodology. Aiming to investigate this drawback, which, to our best knowledge, has no precedents in the literature, we acetalized with 1,2-ethanediol and TsOH in refluxing benzene and in the presence of a Dean–Stark apparatus under various experimental conditions, enantiomerically pure (+)-1. It was found that the extent of racemization depends on the TsOH/(+)-1 and 1,2-ethanediol/(+)-1 ratios. Mechanism hypotheses for this partial and unexpected racemization are provided.

Procedure-Economical, Enantioselective Total Syntheses of Polycyclic Natural Products and Analogues Containing a 3a-Hydroxyhexahydropyrrolo[2,3-b]indole-2-carboxylic Acid Residue

Synlett ◽  
2020 ◽  
Vol 31 (17) ◽  
pp. 1681-1690
Author(s):  
Pei-Qiang Huang
Keyword(s):  
Natural Products ◽  
Carboxylic Acid ◽  
Tandem Reactions ◽  
Protecting Group ◽  
Future Perspectives ◽  
Total Syntheses ◽  
Bioactive Natural Products ◽  
Regioselective Reactions ◽  
Enantioselective Syntheses

The 3a-hydroxyhexahydropyrrolo[2,3-b]indole-2-carboxylic acid (HPIC) residue and its aza-analogue are found in many bioactive natural products. In this account, short divergent total syntheses of several such natural products, diastereomers and analogues are described. It is demonstrated that by appropriate combination of different efficient tactics such as biomimetic/bio-inspired synthesis, chemo/regioselective reactions, umpolung of regioselectivity and/or reactivity, and tandem reactions, the enantioselective syntheses of polycyclic molecules such as (+)-asperlicin E and (–)-robustanoids A and B can be achieved in a protecting-group-free and redox-economical manner, in only three to four steps starting from l-tryptophan.1 Introduction2 Strategic Considerations2.1 Occurrence of HO-HPIC and HO-aza-HPIC Residues in Natural Products2.2 Biosyntheses of HO-HPIC and HO-aza-HPIC Residues2.3 Chemical Syntheses of HO-HPIC and HO-aza-HPIC Residues3 Procedure-Economical Syntheses of HO-HPIC-Containing Natural Products3.1 Protecting-Group-Free Syntheses of Asperlicin E, Its Diastereomer, and an Analogue3.2 Divergent Syntheses of (–)-Robustanoids A and B, a Diastereomer, and Analogues4 Conclusion and Future Perspectives

Biotransformations of Bioactive Natural Products with Complicated Structures

Planta Medica ◽  
2012 ◽  
Vol 78 (05) ◽  
Author(s):  
JG Dai ◽  
RD Chen ◽  
D Xie ◽  
JH Li ◽  
K Wang ◽  
...  
Keyword(s):  
Natural Products ◽  
Bioactive Natural Products

Pyrone-derived Marine Natural Products: A Review on Isolation, Bio-activities and Synthesis

2020 ◽  
Vol 24 (4) ◽  
pp. 354-401 ◽  
Author(s):  
Keisham S. Singh
Keyword(s):  
Natural Products ◽  
Marine Natural Products ◽  
Marine Fungi ◽  
Kojic Acid ◽  
Biological Activities ◽  
Biological Significance ◽  
Pyrone Ring ◽  
Enol Ethers ◽  
Bioactive Natural Products ◽  
Marine Metabolites

Marine natural products (MNPs) containing pyrone rings have been isolated from numerous marine organisms, and also produced by marine fungi and bacteria, particularly, actinomycetes. They constitute a versatile structure unit of bioactive natural products that exhibit various biological activities such as antibiotic, antifungal, cytotoxic, neurotoxic, phytotoxic and anti-tyrosinase. The two structure isomers of pyrone ring are γ- pyrone and α-pyrone. In terms of chemical motif, γ-pyrone is the vinologous form of α- pyrone which possesses a lactone ring. Actinomycete bacteria are responsible for the production of several α-pyrone compounds such as elijopyrones A-D, salinipyrones and violapyrones etc. to name a few. A class of pyrone metabolites, polypropionates which have fascinating carbon skeleton, is primarily produced by marine molluscs. Interestingly, some of the pyrone polytketides which are found in cone snails are actually synthesized by actinomycete bacteria. Several pyrone derivatives have been obtained from marine fungi such as Aspergillums flavus, Altenaria sp., etc. The γ-pyrone derivative namely, kojic acid obtained from Aspergillus fungus has high commercial demand and finds various applications. Kojic acid and its derivative displayed inhibition of tyrosinase activity and, it is also extensively used as a ligand in coordination chemistry. Owing to their commercial and biological significance, the synthesis of pyrone containing compounds has been given attention over the past years. Few reviews on the total synthesis of pyrone containing natural products namely, polypropionate metabolites have been reported. However, these reviews skipped other marine pyrone metabolites and also omitted discussion on isolation and detailed biological activities. This review presents a brief account of the isolation of marine metabolites containing a pyrone ring and their reported bio-activities. Further, the review covers the synthesis of marine pyrone metabolites such as cyercene-A, placidenes, onchitriol-I, onchitriol-II, crispatene, photodeoxytrichidione, (-) membrenone-C, lihualide-B, macrocyclic enol ethers and auripyrones-A & B.

Enantioselective Syntheses of Flavonoid Diels-Alder Natural Products: A Review

2018 ◽  
Vol 15 (2) ◽  
pp. 221-229 ◽  
Author(s):  
Shah Bakhtiar Nasir ◽  
Noorsaadah Abd Rahman ◽  
Chin Fei Chee
Keyword(s):  
Natural Products ◽  
Organic Synthesis ◽  
Lewis Acid ◽  
Alder Reaction ◽  
Diels Alder ◽  
Enantioselective Synthesis ◽  
Chiral Ligand ◽  
Asymmetric Syntheses ◽  
Diels Alder Reaction ◽  
Enantioselective Syntheses

Background: The Diels-Alder reaction has been widely utilised in the syntheses of biologically important natural products over the years and continues to greatly impact modern synthetic methodology. Recent discovery of chiral organocatalysts, auxiliaries and ligands in organic synthesis has paved the way for their application in Diels-Alder chemistry with the goal to improve efficiency as well as stereochemistry. Objective: The review focuses on asymmetric syntheses of flavonoid Diels-Alder natural products that utilize chiral ligand-Lewis acid complexes through various illustrative examples. Conclusion: It is clear from the review that a significant amount of research has been done investigating various types of catalysts and chiral ligand-Lewis acid complexes for the enantioselective synthesis of flavonoid Diels-Alder natural products. The results have demonstrated improved yield and enantioselectivity. Much emphasis has been placed on the synthesis but important mechanistic work aimed at understanding the enantioselectivity has also been discussed.

Formation of Carbon-Oxygen Bond Mediated by Hypervalent Iodine Reagents Under Metal-free Conditions

2020 ◽  
Vol 17 ◽  
Author(s):  
Ayesha Jalil ◽  
Yaxin O Yang ◽  
Zhendong Chen ◽  
Rongxuan Jia ◽  
Tianhao Bi ◽  
...  
Keyword(s):  
Natural Products ◽  
Bond Formation ◽  
Building Blocks ◽  
Review Article ◽  
Hypervalent Iodine ◽  
Metal Free ◽  
Bioactive Natural Products ◽  
The Past ◽  
Oxygen Bond ◽  
Privileged Scaffolds

: Hypervalent iodine reagents are a class of non-metallic oxidants have been widely used in the construction of several sorts of bond formations. This surging interest in hypervalent iodine reagents is essentially due to their very useful oxidizing properties, combined with their benign environmental character and commercial availability from the past few decades ago. Furthermore, these hypervalent iodine reagents have been used in the construction of many significant building blocks and privileged scaffolds of bioactive natural products. The purpose of writing this review article is to explore all the transformations in which carbon-oxygen bond formation occurred by using hypervalent iodine reagents under metal-free conditions

scholarly journals Phytoplankton of the Curonian Lagoon as a New Interesting Source for Bioactive Natural Products. Special Impact on Cyanobacterial Metabolites

Biomolecules ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1139
Author(s):  
Donata Overlingė ◽  
Anna Toruńska-Sitarz ◽  
Marta Cegłowska ◽  
Agata Błaszczyk ◽  
Karolina Szubert ◽  
...  
Keyword(s):  
Natural Products ◽  
Serine Proteases ◽  
Ex Situ ◽  
Breast Adenocarcinoma ◽  
Curonian Lagoon ◽  
Bacterial Strains ◽  
Biotechnological Potential ◽  
Bioactive Natural Products ◽  
Field Samples ◽  
Sample Component

The bioprospecting of marine and brackish water systems has increased during the last decades. In this respect, microalgae, including cyanobacteria, and their metabolites are one of the most widely explored resources. Most of the bioactive compounds are isolated from ex situ cultures of microorganisms; however, analysis of field samples could also supply valuable information about the metabolic and biotechnological potential of microalgae communities. In this work, the activity of phytoplankton samples from the Curonian Lagoon was studied. The samples were active against antibiotic resistant clinical and environmental bacterial strains as well as against serine proteases and T47D human breast adenocarcinoma cells. No significant effect was found on Daphnia magna. In addition, using LC-MS/MS, we documented the diversity of metabolites present in field samples. A list of 117 detected cyanopeptides was presented. Cyanopeptolins constituted the largest class of cyanopeptides. As complex bloom samples were analyzed, no link between the observed activity and a specific sample component can be established. However, the results of the study showed a biotechnological potential of natural products from the Curonian Lagoon.

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