A New Stereocontrolled Synthetic Route to (−)-Echinosporin from d-Glucose via Padwa Allenylsulfone [3 + 2]-Anionic Cycloadditive Elimination

Dearomative (3 + 2) Cycloadditions of 3-Nitroheteroarenes with Allenyl Sulfones Mediated by Ion Pair Organocatalysis

We report the first example of dearomative (3 + 2) cycloadditions of 3-nitro(aza)-indole, -benzofuran, and -benzothiophene derivatives in the presence of allenyl sulfones, using sulfinate ammonium ion pairs as organocatalytic promoters. The methodology provides a new, facile, and efficient protocol for the synthesis of functionalized 2,3-fused cyclopentannulated indolines and dihydrobenzofurans.

Synthesis of Seven-Membered Ring Nucleosides and Serendipitous Simmons-Smith O-Glycosylation

A series of seven-membered (oxepine) nucleosides containing various nucleobases (A, U, T, 5-FU, C) were synthesized by ring expansion of cyclopropanated glucals. We expect this new series of ring-expanded nucleic acid analogues to be useful as building blocks in the design of mixed base functional genetic systems. While exploring alternative pathways to oxepine nucleoside synthesis, we discovered an unprecedented α-stereoselective O-glycosylation of 1,2-glucals under mild Simmons-Smith conditions.

Amycolasporins and Dibenzoyls from Lichen-Associated Amycolatopsis hippodromi and Their Antibacterial and Anti-inflammatory Activities

Eleven metabolites, six echinosporins (1-6), four dibenzoyls (7-10), and an aromatic compound (11), were isolated from the fermentation broth of lichen-associated Amycolatopsis hippodromi. The structures of the new compounds (1-5, 8-11) were elucidated by comprehensive spectroscopic analysis including data from experimental and calculated ECD spectra. Amycolasporins A-C (1-3) demonstrated antibacterial activities against Bacillus subtilis, Staphylococcus aureus, and Escherichia coli with MIC values of 25 or 100 μg/mL. Amycolasporin C (3) and the known dibenzoyl (7) attenuated the production of NO due to the suppression of the expression of nitric oxide synthase (iNOS) in LPS-induced RAW 264.7 cells in a dose-dependent manner.

Recent developments in the chemistry of allenyl sulfones

Allenyl sulfones are versatile building blocks for the construction of various acyclic, carbocyclic and heterocyclic motifs. Recent developments in the preparation and synthetic applications of allenyl sulfones are summarised.

Echinosporin antibiotics isolated from Amycolatopsis strain and their antifungal activity against root-rot pathogens of the Panax notoginseng

Actinomycete strain YIM PH20520, isolated from the rhizosphere soil sample of Panax notoginseng collected in Wenshang, Yunnan Province, China, exhibited antifungal activity against root-rot pathogens of the Panax notoginseng. The structures of bioactive molecules, isolated from the ethyl acetate extract of the fermentation broth of the strain, were identified as echinosporin (1) and 7-deoxyechinosporin (2) based on extensive spectroscopic analyses. 1 exhibited antifungal activity against four tested root-rot pathogens of Panax notoginseng include Fusarium oxysporum, Fusarium solani, Alternaria panax, and Phoma herbarum with the MIC value at 64, 64, 32, and 64 μg/mL, respectively. 2 exhibited antifungal activities against F. oxysporum, F. solani, A. panax, and P. herbarum with the MIC value at 128, 128, 64, and 128 μg/mL, respectively. Based on the phylogenetic analyses, the closest phylogenetic relative of strain YIM PH20520 is Amycolatopsis speibonae JS72^T (97.69%), so strain YIM PH20520 was identified as Amycolatopsis strain. To the best of our knowledge, this is the first report of echinosporin antibiotics isolated from Amycolatopsis strain besides Streptomyces strain and their antifungal activity against four tested root-rot pathogens of the Panax notoginseng. The results provide a reliable evidence for the following related biosynthetic investigations on Amycolatopsis strain YIM PH20520 due to echinosporins antibiotics' unique tricyclic acetal-lactone structures.

Regiodivergent synthesis of 1- and 2-arylsulfonyl 1,3-dienes

In the course of a study of the alkoxyallylation of allenic sulfones through the use of π-allylpalladium chemistry, we discovered an isomerization of allenic sulfones to arylsulfonyl 1,3-dienes. Under conditions of palladium catalysis in the presence of acids such as acetic acid, allenic sulfones are converted to 1-arylsulfonyl 1,3-dienes. On the other hand, nucleophilic catalysis using triphenylphosphine in the presence of a proton shuttle yields 2-arylsulfonyl 1,3-dienes. Thus, either regioisomer of the arylsulfonyl diene can be prepared at will based on changes in reaction conditions.