Sequential Claisen Research Articles

Moving away from traditional antibiotic treatment: can macrocyclic lactones from marine macroalga-associated heterotroph be the alternatives?

Intertidal red algae Hypnea valentiae associated Bacillus amyloliquefaciens MTCC 12716 revealed potential inhibitory effects on the growth of drug-resistant pathogens. In the genome of B. amyloliquefaciens MTCC 12716, biosynthetic gene clusters encoding antibacterial metabolites were predicted, which might be expressed and contributed to the broad-spectrum anti-infective activity. Three homologue members of the 24-membered macrocyclic lactone family, named as bacvalactones 1-3 bearing 13-O-ethyl (1); 15-O-furanyl-13-O-isobutyl-7-O-propyl-propanoate (2); and 15-O-furanyl-13-O-isobutyl-7-O-propyl-propanoate-7,24-dimethyl (3) functionalities, were acquired through bioactivity-guided purification. The macrocyclic lactones displayed bactericidal activity against opportunistic pathogens causing nosocomial infections, for instance, methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus faecalis (VREfs), and multidrug-resistant strains of Pseudomonas aeruginosa and Klebsiella pneumonia with MIC ≤ 3.0μg/mL, whereas standard antibiotics ampicillin and chloramphenicol were active only at concentrations of ≥ 6.25mg/mL. The biosynthetic pathway of macrocyclic lactones that are generated by trans-AT polyketide synthases through stepwise extension of an acetyl starter unit by eleven sequential Claisen condensations with malonyl-CoA was established, and the structures were correlated with the gene organization of the mln operon, which encompasses nine genes mln A-I (approximately 47kb in size). The best binding poses for each compounds (1-3) with Staphylococcus aureus peptide deformylase (SaPDF) unveiled docking scores (≥ 9.70kcal/mol) greater than that of natural peptide deformylase inhibitors, macrolactin N and actinonin (9.14 and 6.96kcal/mol, respectively), which supported their potential in vitro bioactivities. Thus, the present work demonstrated the potential of macrocyclic lactone for biotechnological and pharmaceutical applications against emerging multidrug-resistant pathogens. Key Points •Three antibacterial bacvalactones were identified from the symbiotic bacterium. •The symbiotic bacterial genome was explored to identify the biosynthetic gene clusters. •Trans-AT pks-assisted mln biosynthetic pathway of the macrocyclic lactone was proposed. •In silicomolecular interactions of the bacvalactones with S. aureus PDF were analyzed.

An Approach to the Synthesis of 1-Propenylnaphthols and 3-Arylnaphtho[2,1-b]furans.

A simple and efficient strategy for the synthesis of 1-propenylnaphthols from readily accessible 3-arylallylnaphthyl ethers has been developed. By using K2CO3 as base and 2-methoxyethanol as solvent, direct access to a wide range of 1-propenylnaphthols can be achieved in generally good yield (up to 99%) with high stereoselectivity toward the Z isomer. The control experiments indicate that the reaction proceeds through a sequential Claisen rearrangement/isomerization process. Furthermore, starting from the same material, the highly valuable 3-arylnaphtho[2,1-b]furans can be obtained in N,N-dimethylformamide and in the presence of Ag2O as the oxidant via a one-pot sequential Claisen rearrangement/isomerization/cyclization reaction. Mechanistic studies confirm that 1-propenylnaphthols are the key intermediates to form the 3-arylnaphtho[2,1-b]furans. In addition, these two operationally simple and practical protocols could be scaled up to a gram level.

ChemInform Abstract: Synthesis of Vinylcyclopropanes by Allylation/Ring‐Closing Metathesis/Claisen Rearrangement.

Abstract A facile double allylation/ring-closing metathesis/Claisen rearrangement route for preparing vinylcyclopropanes 6 is developed. The efficient synthesis includes O-allylation of α-allyl-α-sulfonylketones 8 with allylic bromides, ring-closing metathesis of diallyl compounds 9 and sequential Claisen rearrangement of the resulting oxepines.

Synthesis of vinylcyclopropanes by allylation/ring-closing metathesis/Claisen rearrangement

A facile double allylation/ring-closing metathesis/Claisen rearrangement route for preparing vinylcyclopropanes 6 is developed. The efficient synthesis includes O-allylation of α-allyl-α-sulfonylketones 8 with allylic bromides, ring-closing metathesis of diallyl compounds 9 and sequential Claisen rearrangement of the resulting oxepines.

ChemInform Abstract: Synthesis of Phosphorus Containing Medium Ring Heterocycles by Sequential Claisen Rearrangement and Ring Closing Metathesis.

AbstractThe precursors (I), (V), and (VIII) are prepared from the corresponding phenols by Claisen rearrangement.

Synthesis of phosphorus containing medium ring heterocycles by sequential Claisen rearrangement and ring closing metathesis

An efficient method for the synthesis of novel medium ring phosphorus containing heterocycles starting from phenol derivatives by ruthenium catalyzed ring closing metathesis is described. This work deals with a sequential aromatic Claisen-rearrangement, coupling of an allyl/vinyl phosphonate, and ring closing metathesis reaction. All of these reactions were carried out at ambient temperature to afford the medium-sized phosphorus heterocycles in excellent yields.

Stilbene–Chalcone Hybrids: Design, Synthesis, and Evaluation as a New Class of Antimalarial Scaffolds That Trigger Cell Death through Stage Specific Apoptosis

Novel stilbene-chalcone (S-C) hybrids were synthesized via a sequential Claisen-Schmidt-Knoevenagel-Heck approach and evaluated for antiplasmodial activity in in vitro red cell culture using SYBR Green I assay. The most potent hybrid (11) showed IC(50) of 2.2, 1.4, and 6.4 μM against 3D7 (chloroquine sensitive), Indo, and Dd2 (chloroquine resistant) strains of Plasmodium falciparum, respectively. Interestingly, the respective individual stilbene (IC(50) > 100 μM), chalcone (IC(50) = 11.5 μM), or an equimolar mixture of stilbene and chalcone (IC(50) = 32.5 μM) were less potent than 11. Studies done using specific stage enriched cultures and parasite in continuous culture indicate that 11 and 18 spare the schizont but block the progression of the parasite life cycle at the ring or the trophozoite stages. Further, 11 and 18 caused chromatin condensation, DNA fragmentation, and loss of mitochondrial membrane potential in Plasmodium falciparum, thereby suggesting their ability to cause apoptosis in malaria parasite.

ChemInform Abstract: Studies in Sulfur Heterocycles. Part 16. Use of 7-Hydroxy-1-benzothiophene in the Synthesis of Substituted Benzothiophene Derivatives and Tricyclic Compounds Incorporating a Fused Thiophene Ring.

Heteroatom directed ortho-metallation on N,N-diethyl-7-carbamoyloxy-1-benzothiophene, readily available from 7-hydroxy-1-benzothiophene enabled regioselective substitution in the 6-position. Both 7- and 4-hydroxy-1-benzothiophene were used in the annelation of 5- or 6-membered oxygen heterocycles onto the 1-benzothiophene molecule through sequential Claisen rearrangement–ring closure reactions. The nature of the annelated ring depends upon the reaction conditions.

ChemInform Abstract: Sequential Claisen Rearrangement and Intramolecular Heck Reaction as a Route to Medium‐Ring Oxacycle‐Fused Heterocycles.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

An Efficient Synthesis of 4'-Vinylated Carbocyclic Nucleoside Analogues via Two Directional Ring-closing Metathesis

Two directional ring-closing metathesis (RCM) was applied successfully to the synthesis of 4'-vinylated carbocyclic nucleoside analogues from the trivinyl intermediate 12, which was readily made using a sequential Claisen rearrangement and ring-closing metathesis (RCM) starting from Weinreb amide 5. An antiviral evaluation of the synthesized compounds against various viruses such as HIV, HSV-1, HSV-2 and HCMV revealed that the guanine analogue 20 have moderate anti-HIV activity in the MT-4 cell line (<TEX>$EC_{50}$</TEX> = 10.2 <TEX>$\mu$</TEX> M).

Sequential Claisen Rearrangement and Intramolecular Heck Reaction as a Route to Medium-Ring Oxacycle-Fused Heterocycles

A synthetic strategy based on tandem application of Claisen rearrangement and intramolecular Heck reaction as key steps has been developed for the synthesis of various hitherto unknown benzoxocine- and benzoxonine-fused coumarin and quinolone derivatives.

Sequential Thermal and Catalyzed Claisen Rearrangements Toward the Synthesis of Thiocoumarin-Annulated Furopyrans

Regioselective synthesis of a hitherto unreported thiocoumarin-annulated furopyran moiety was achieved by the application of Claisen rearrangement in which a second Claisen rearrangement was achieved by anhydrous aluminum chloride. The precursor endocyclic compounds for catalyzed Claisen rearrangement were synthesized by the thermal [3,3] sigmatropic rearrangement of the corresponding ether. Keywords: Anhydrous aluminum chloride, sequential Claisen rearrangement, intramolecular hydroaryloxylation, furopyrans, 4-hydroxythiocoumarin, 1-aryloxy-4-chlorobut-2-yne

ChemInform Abstract: Studies on Sequential Claisen Rearrangement: Charge‐Accelerated [3,3]‐Sigmatropic Rearrangement Leading to Polyheterocycles.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Aluminium Chloride–Catalyzed Claisen Rearrangement: Synthesis of Polyheterocycles Containing Oxygen, Nitrogen, and Sulfur

Synthesis of 1,8‐naphthyridine‐annulated polyheterocycles containing oxygen, nitrogen, and sulfur has been achieved by thionation and sequential Claisen rearrangement of 4‐(4′‐aryloxybut‐2′‐ynyloxy)‐1‐phenyl[1,8]‐naphthyridin‐2‐ones first by heating in 1,2‐dichlorobenzene for 1–2 h and then by anhydrous AlCl3‐catalyzed Claisen rearrangement in dichloromethane for 1 h.

Lewis acid catalyzed Claisen rearrangement: Regioselective synthesis of oxygen, nitrogen, and sulfur heterocycles

Regioselective synthesis of pentacyclic heterocycles containing oxygen, nitrogen, and sulfur has been achieved in good to excellent yields by the sequential Claisen rearrangement of but-2-ynyl ethers and sulfides containing quinolone moiety. The substrates ethers and sulfides were prepared from 1-aryloxy-4-chlorobut-2-ynes with N-alkyl-4-hydroxyquinoline-2(1H)-ones.Key words: regioselectivity, [3,3] sigmatropic rearrangement, nucleophilicity of sulfur, aluminium chloride, heterocycles.

Formal synthesis of (−)-morphine from d-glucal based on the cascade Claisen rearrangement

The formal synthesis of (−)-morphine is described. The C-ring in morphine was prepared in an optically pure form from d-glucal using Ferrier’s carbocyclization reaction, and the vicinal tertiary and quaternary stereocenters in the C-ring were stereoselectively generated in a one-step reaction based on the cascade sequential Claisen rearrangement of an allylic vicinal diol derivative. After the one-step formation of the dibenzofuran structure, the intramolecular Friedel–Crafts type reaction effectively constructed the ABCE-phenanthrofuran skeleton. Introduction of a tosylamide function, followed by reductive cyclization furnished (−)-dihydroisocodeine, the known synthetic intermediate for (−)-morphine.

Studies on Sequential Claisen Rearrangement: Charge‐Accelerated [3,3]‐Sigmatropic Rearrangement Leading to Polyheterocycles

A number of quinolone‐annulated pentacycles have been regioselectively synthesized in 90–95% yields by sequential Claisen rearrangements. The second synthesis is anhydrous AlCl3‐catalyzed charge‐accelerated aromatic Claisen rearrangement of 1‐aryloxymethyl‐6‐alkyl‐3H‐pyrano[2,3‐c]quinolin‐5(6H)‐ones in dichloromethane at rt for 5–10 min. The precursors were synthesized by the thermal [3,3]‐sigmatropic rearrangement of the corresponding ethers.

Regioselective synthesis of polyheterocyclic scaffolds by sequential [3,3] sigmatropic rearrangements and pyridine hydrotribromide mediated heterocyclization

Abstractmagnified imageA number of tetracyclic polyhetero scaffolds have been regioselectively synthesised in 70‐75% yield from 4‐[(3‐aryloxy‐2‐propynyl)oxy]‐6‐methyl‐pyran‐2‐ones via thionation of the lactone carbonyl, sequential Claisen rearrangements and pyridine hydrotribromide mediated heterocyclization.

Synthetic Studies on Macrolactin A: Construction of C4−C24 Fragment

The preparation of the C4-C24 fragment of the macrolactin A is described. The adopted synthetic strategy involves two isomerizations to selectively construct the (8E,10Z) and (16E,18E) dienes, using a sequential Claisen rearrangement/allene isomerization and a Ph3P-catalyzed isomerization of an yne-one, respectively.

Regioselective synthesis of biologically interesting pentacyclic polyheterocycles by sequential thio-Claisen and AlCl3 catalyzed oxy-Claisen rearrangement of 4-(4′-aryloxybut-2′-ynylthio)-1-phenyl-1,8-naphthyridin-2(1H)-one

A number of 4-aryloxymethyl-6-phenyl-2H-thiopyrano[3,2-c][1,8]naphthyridin-5(6H)-ones were regio selectively synthesized in 82%–95% yields by the thermal Claisen rearrangement of 4-(4′-aryloxybut-2′-ynylthio)-1-phenyl-[1,8]naphthyridin-2(1H)-ones. These products were then subjected to a second Claisen rearrangement in the presence of a Lewis acid catalyst, anhyd. AlCl3, to give hitherto unreported pentacyclic heterocycles in 75%–90% yields. The same final products were also obtained in low yield upon refluxing 4-aryloxymethyl-6-phenyl-2H-thio pyrano-[3,2-c][1,8]naphthyridin-5(6H)-ones in N,N-diethyl aniline for 12–14 h. This method was found to be more effective than thermal Claisen rearrangement.Key words: [3,3] sigmatropic rearrangement, regioselective synthesis, phase transfer catalysis, sequential Claisen rearrangement, Lewis acid catalyzed Claisen rearrangement, single crystal X-ray.