A [6+4]-cycloaddition adduct is the biosynthetic intermediate in streptoseomycin biosynthesis

Streptoseomycin (STM, 1) is a bacterial macrolactone that has a unique 5/14/10/6/6-pentacyclic ring with an ether bridge. We have previously identified the biosynthetic gene cluster for 1 and characterized StmD as [6 + 4]- and [4 + 2]-bispericyclase that catalyze a reaction leading to both 6/10/6- and 10/6/6-tricyclic adducts (6 and 7). The remaining steps, especially how to install and stabilize the required 10/6/6-tricyclic core for downstream modifications, remain unknown. In this work, we have identified three oxidoreductases that fix the required 10/6/6-tryciclic core. A pair of flavin-dependent oxidoreductases, StmO1 and StmO2, catalyze the direct hydroxylation at [6 + 4]-adduct (6). Subsequently, a spontaneous [3,3]-Cope rearrangement and an enol-ketone tautomerization result in the formation of 10/6/6-tricyclic intermediate 12b, which can be further converted to a stable 10/6/6-tricyclic alcohol 11 through a ketoreduction by StmK. Crystal structure of the heterodimeric complex NtfO1-NtfO2, homologues of StmO1-StmO2 with equivalent function, reveals protein-protein interactions. Our results demonstrate that the [6 + 4]-adduct instead of [4 + 2]-adduct is the bona fide biosynthetic intermediate.

2-O-Monoalkyl isosorbide ethers with C8, C10, C12 and C14 chain lengths

The title compounds, 6-(octyloxy)hexahydrofuro[3,2-b]furan-3-ol, C14H26O4, 6-(decyloxy)hexahydrofuro[3,2-b]furan-3-ol, C16H30O4, 6-(dodecyloxy)hexahydrofuro[3,2-b]furan-3-ol, C18H34O4, and 6-(tetradecyloxy)hexahydrofuro[3,2-b]furan-3-ol, C20H38O4, consist of a polar headgroup (isosorbide) and a lipophilic alkyl chain linked via an ether bridge. Isosorbide is a biobased diol, containing two fused furan rings. One intermolecular hydrogen bond connects the molecules between the free endo hydroxy group and the opposing ether oxygen of the V-shaped head group. Thus the molecule layers interlock like in a herringbone pattern parallel to the bc plane.

Chemical synthesis and biological activity of peptides incorporating an ether bridge as a surrogate for a disulfide bond

We report the first introduction of an ether linkage as surrogate into the disulfide-rich peptides using ether-containing diaminodiacid.

Nickel-assisted complete cleavage of CO by a silylene/siliconoid hybrid under formation of an SiC enol ether bridge

A silylene-siliconoid hybrid incorporates CO to form a SiC enol ether bridge in the presence of Ni(cod)2 ( = silicon).

An ether bridge between cations to extend the applicability of ionic liquids in electric double layer capacitors

Linking 5% cations with an ether bridge prevents EMIm-TFSI crystallization at low temperatures and promotes the performance of the resultant EDLC.