Saturated oxygen heterocycles are widely found in a broad array of natural products and other biologically active molecules. In medicinal chemistry, small and medium rings are also important synthetic intermediates since they can undergo ring-opening and -expansion reactions. These applications have driven numerous studies on the synthesis of oxygen-containing heterocycles and considerable effort has been devoted toward the development of methods for the construction of saturated oxygen heterocycles. This paper provides an overview of the biological roles and synthetic strategies of saturated cyclic ethers, covering some of the most studied and newly discovered related natural products in recent years. This paper also reports several promising and newly developed synthetic methods, emphasizing 3-7 membered rings.

https://www.mdpi.com/1420-3049/24/20/3778/pdf

An Overview of Saturated Cyclic Ethers: Biological Profiles and Synthetic Strategies

Marine natural products play critical roles in the chemical defense of many marine organisms and are essential, reputable sources of successful drug leads. Sixty-seven 14-membered resorcylic acid lactone derivatives 3–27 and 30–71 of the natural product zeaenol (1) isolated from the marine-derived fungus Cochliobolus lunatus were semisynthesized by chlorination, acylation, esterification, and acetalization in one to three steps. The structures of these new derivatives were established by HRESIMS and NMR techniques. All the compounds (1–71) were evaluated for their antialgal and antiplasmodial activities. Among them, 14 compounds displayed antifouling activities against adhesion of the fouling diatoms. In particular, 9 and 34 exhibited strong and selective inhibitory effects against the diatoms Navicula laevissima and Navicula exigua (EC50 = 6.67 and 8.55 μmol/L), respectively, which were similar in efficacy to those of the positive control SeaNine 211 (EC50 = 2.90 and 9.74 μmol/L). More importantly, 38, 39, and 69–71 showed potent antiplasmodial activities against Plasmodium falciparum with IC50 values ranging from 3.54 to 9.72 μmol/L. Very interestingly, the five antiplasmodial derivatives displayed non-toxicity in the cytotoxicity assays and the zebrafish embryos model, thus, representing potential promising antiplasmodial drug agents. The preliminary structure–activity relationships indicated that biphenyl substituent at C-2, acetonide at positions C-5′ and C-6′, and tri- or tetra-substituted of acyl groups increased the antiplasmodial activity. Therefore, combining evaluation of chemical ecology with pharmacological models will be implemented as a systematic strategy, not only for environmentally friendly antifoulants but also for structurally novel drugs.

/pdf/structure-modification-antialgal-antiplasmodial-and-toxic-2lv417wz8y.pdf

Structure modification, antialgal, antiplasmodial, and toxic evaluations of a series of new marine-derived 14-membered resorcylic acid lactone derivatives

Total synthesis: the structural confirmation of natural products

Metathesis reactions in total‐ and natural product fragments syntheses

A unified and concise first asymmetric total synthesis of (-)-citreoisocoumarin (2), (-)-citreoisocoumarinol (3), 12-epi-citreoisocoumarinol (4), and (-)-mucorisocoumarins A (5) and B (6) have been accomplished from the common intermediate (-)-6-O-methyl-citreoisocoumarin (1). Central to the synthetic approach is a regioselective gold(I)-catalyzed 6-endo-dig cyclization strategy for the construction of the isocoumarin skeleton. The other key steps in this approach included Sonogashira coupling, Tsuji-Wacker oxidation, Evans-Saksena's 1,3-anti-reduction, and Narasaka-Prasad's 1,3-syn-reduction. The synthetic results unambiguously confirmed the absolute configuration of the natural products mucorisocoumarins A and B as (-)-(10R,12S)-5 and (+)-(10S,12S)-6, respectively.

Total Synthesis of (-)-Citreoisocoumarin, (-)-Citreoisocoumarinol, (-)-12-epi-Citreoisocoumarinol, and (-)-Mucorisocoumarins A and B Using a Gold(I)-Catalyzed Cyclization Strategy.

A General Diastereoselective Strategy for Both cis- and trans-2,6-Disubstituted Tetrahydropyrans: Formal Total Synthesis of (+)-Muconin

Total Synthesis and Structural Revision of Monocillin VII.

The present manuscript describes a convenient, mild, and highly stereoselective method for the allylation of δ-hydroxy-α,β-unsaturated ketones having a benzylic hydroxyl group at the δ-position using allyltrimethylsilane mediated by BF3·OEt2, leading to 2,4-diallyl-2-methyl-6-aryltetrahydro-2H-pyran ring systems with quaternary carbon stereogenic centers. This represents the first example of a tandem isomerization followed by one C-O and two C-C bond-forming reactions in one pot. The isolation of TMS-protected lactol as an intermediate from the reaction strongly supports the proposed mechanistic pathway.

BF3·OEt2-Catalyzed Unexpected Stereoselective Formation of 2,4-trans-Diallyl-2-methyl-6-aryltetrahydro-2H-pyrans with Quaternary Stereocenters

General Asymmetric Synthetic Strategy for the α-Alkylated 2,5,6-Trisubstituted Pyran of Indanomycin and Related Natural Products

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A General Diastereoselective Strategy for Both cis- and trans-2,6-Disubstituted Tetrahydropyrans: Formal Total Synthesis of (+)-Muconin

Total Synthesis and Structural Revision of Monocillin VII.

BF3·OEt2-Catalyzed Unexpected Stereoselective Formation of 2,4-trans-Diallyl-2-methyl-6-aryltetrahydro-2H-pyrans with Quaternary Stereocenters

General Asymmetric Synthetic Strategy for the α-Alkylated 2,5,6-Trisubstituted Pyran of Indanomycin and Related Natural Products