Backbone-extended amino acids have a variety of potential applications in peptide and protein science, particularly if the geometry of the amino acid is controllable. Here we describe the synthesis of δ-amino acids that contain three vicinal C-F bonds positioned along the backbone. The ultimately successful synthetic approach emerged through the investigation of several methods based on both el...

The first syntheses are described of the four enantiopure naphthopyranquinones (1R,3R,4S)- and (1R,3R,4R)-3,4-dihydro-4,7,9-trihydroxy-1,3-dimethylnaphtho[2,3-c]pyranquinone (quinone A 1 and quinone A' 2) and their two C-3 epimers, the (1R,3S,4S)- and (1R,3S,4R)-diastereoisomers 5 and 6, using enantiopure lactate as the source of asymmetry. Key factors in these syntheses are the maintenance of ...

Two diastereoisomers of the title compound, C(25)H(26)N(2)O, have been prepared by cyclo-addition between 1,3,3-trimethyl-2-methyl-eneindoline and C-phenyl-N-phenyl-nitrone. The stereochemistry of the major diastereoisomer, viz. S,R/R,S, is confirmed by the X-ray analysis. The oxazole and the pyrole rings have envelope conformations. The packing is stabilized by weak C-H⋯π inter-actions involvi...

Electron ionization mass spectrometry and density functional theory (DFT) calculations have been used to study the fragmentation of diastereoisomers of protected 1,2-diaminoalkylphosphonic acids. The loss of a diethoxyphosphoryl group and the elimination of diethyl phosphonate were found to be competitive fragmentation processes, which can be used to differentiate both stereoisomers. Selective ...

H etero-Diels-Alder Reaction, a,/?-Unsaturated Ketones, Styrenes Cycloadditions of 3-aryl-2-benzoyl-2-propenenitriles la,b to styrene (2a) and its methylor methoxy-substituted derivatives 2b-d proceed regioand diastereoselectively yielding cis and trans diastereoisomers of 2,4,6-triaryl-3,4-dihydro-2//-pyran-5-carbonitriles 3 and 4 in 59-72% yield. Cycloadducts cis-3 were the major products. Re...

Amongthe methods for racemization testing in peptide synthesis, the GLCmethod is a simple one and the most practicable, especially when a packed column is used. In this method Tfa-Pro-X-OH (X=amino acids) is coupled with H-Val-Pro-OMe, the resulting Tfa-tetrapeptide-OMe is separated by GLC, and the degree of recemization is estimated from the ratio of the peaks separated to the diastereoisomers...

We describe a rational approach devoted to modulate the sugar-phosphate backbone geometry of nucleic acids. Constraints were generated by connecting one oxygen of the phosphate group to a carbon of the sugar moiety. The so-called dioxaphosphorinane rings were introduced at key positions along the sugar-phosphate backbone allowing the control of the six-torsion angles α to ζ defining the polymer...

The intermolecular [2 + 2]-photocycloaddition of the parent flavone molecule (4) as triplet energy-accepting species and electron-rich alkene 2, 3-dihydrofuran (5) was performed by visible-light-mediated triplet-sensitization with an iridium-based organometallic sensitizer. reaction proceeds high diastereo- regioselectivity (>98:2 for regiochemical orientation 95% d.s.). In contrast to numer...

Herein, we describe the synthesis, structural characterization, and synthetic use as an advanced intermediate of a cross-stapled alkene-bridged hexapeptide to mimic the DE-ring of the lantibiotic nisin. The linear precursor was cyclized by ring-closing metathesis to give the correctly folded bicyclic hexapeptide in a single step, and the four individual diastereoisomers were isolated, structura...