A Total Synthesis of the Natural Enantiomer of the Gastroprotective Natural Products AI-77-B and Amicoumacin C Hydrochloride

Concise synthesis of amino acid component of amicoumacins via dihydrooxazine formation through intramolecular conjugate addition

Amicoumacins are a family of antibiotics with a variety of important bioactivities. A concise and efficient method was developed for synthesizing the amino acid component of amicoumacins via the corresponding dihydrooxazine intermediate. The dihydrooxazine ring was formed with complete stereoselectivity through an intramolecular conjugate addition of a δ-trichloroacetimidoyloxy-α,β-unsaturated ester, which was obtained from a known 4,6-O-p-methoxybenzylidene-protected d-glucose. The synthesis developed in this study can be used to synthesize the building blocks of amicoumacins and can likely be adapted for the synthesis of other types of molecules possessing dihydrooxazine rings or amino alcohol moieties.

Application of Pd-Catalyzed C-H Alkylation Reaction in Total Syntheses of Twelve Amicoumacin-Type Natural Products

Enantioselective total syntheses of 12 amicoumacin-type natural products are accomplished with a palladium(II)-catalyzed C-H alkylation as the key step to furnish the 3,4-dihydroisocoumarin scaffold. The target chemicals are assembled in a convergent protocol by merging 3,4-dihydroisocoumarin derived amine part with categories of acid segments that are efficiently prepared by chemoselective catalytic oxidation of chiral 1,2-dihydroxyethylfuran-2(5H)-ones. Afterward, the cytotoxicity of amicoumacins on five cancer cell lines and one normal cell line is investigated.

Asymmetric Total Synthesis of Hetiamacins A-F

Herein, we report a concise and stereoselective approach for the asymmetric total synthesis of hetiamacins A-F on the basis of the total synthesis of amicoumacin C, which could be synthesized from a known l-aspartic acid derivative. The synthesis of hetiamacin A was accomplished by an 11-step sequence that featured 1,3-oxazinane ring formation of amicoumacin B followed by amidation in one pot. Hetiamacins B-F were synthesized from amicoumacin A in only one step.

Activating and Attenuating the Amicoumacin Antibiotics

The amicoumacins belong to a class of dihydroisocoumarin natural products and display antibacterial, antifungal, anticancer, and anti-inflammatory activities. Amicoumacins are the pro-drug activation products of a bacterial nonribosomal peptide-polyketide hybrid biosynthetic pathway and have been isolated from Gram-positive Bacillus and Nocardia species. Here, we report the stimulation of a “cryptic” amicoumacin pathway in the entomopathogenic Gram-negative bacterium Xenorhabdus bovienii, a strain not previously known to produce amicoumacins. X. bovienii participates in a multi-lateral symbiosis where it is pathogenic to insects and mutualistic to its Steinernema nematode host. Waxmoth larvae are common prey of the X. bovienii-Steinernema pair. Employing a medium designed to mimic the amino acid content of the waxmoth circulatory fluid led to the detection and characterization of amicoumacins in X. bovienii. The chemical structures of the amicoumacins were supported by 2D-NMR, HR-ESI-QTOF-MS, tandem MS, and polarimeter spectral data. A comparative gene cluster analysis of the identified X. bovienii amicoumacin pathway to that of the Bacillus subtilis amicoumacin pathway and the structurally-related Xenorhabdus nematophila xenocoumacin pathway is presented. The X. bovienii pathway encodes an acetyltransferase not found in the other reported pathways, which leads to a series of N-acetyl-amicoumacins that lack antibacterial activity. N-acetylation of amicoumacin was validated through in vitro protein biochemical studies, and the impact of N-acylation on amicoumacin’s mode of action was examined through ribosomal structural analyses.

Stereoselective Synthesis of Dihydroisocoumarin Moiety of Microbial Agent AI-77-B: a Diels-Alder Based Strategy

The dihydroisocoumarin fragment of the gastroprotective natural product AI-77-B has been synthesized in optically active form by using a regiospecific Diels-Alder reaction of 1-methoxy-1,3-cyclohexadiene and an acetylenic ester derivative, prepared stereoselectively from leucinal.

A New Palladium-Catalyzed Intramolecular Allylation to Pyrrolidin-2-ones(1)

A novel palladium(0)-catalyzed cyclization to 3,4-disubstituted pyrrolidin-2-ones has been developed. The new approach relies upon the concomitant generation of stabilized acetamide enolate anions and of a pi-allyl-palladium appendage, properly tethered by a nitrogen atom. Reaction conditions have been optimized for the methoxycarbonyl-stabilized model reaction [(Z)-2 --> 3] and then applied to other substrates. A broad range of acetamide anion stabilizers was shown to allow the desired intramolecular C-C bond formation (MeO(2)C, MeCO, NC, (EtO)(2)PO, PhSO(2)). The cyclizations gave exclusively 5-exo-trig ring closure, thereby affording gamma-lactams. All the cyclizations gave the corresponding 3,4-disubstituted pyrrolidin-2-ones with total diastereoselection. Complete trans preference was unequivocally demonstrated for the model reaction via a NOESY experiment.