Helical oligoproline arrays provide a structurally well-defined environment for building photochemical energy conversion assemblies. The use of solid-phase peptide synthesis (SPPS) to prepare four such arrays, consisting of 16, 17, 18, and 19 amino acid residues, is described here. Each array contains the chromophore [Rub'(2)m](PF(6))(2) (b' = 4,4'-diethylamidocarbonyl-2,2'-bipyridine; m = 4-methyl-2,2'-dipyridine-4'-carboxylic acid) and the electron transfer donor PTZ (phenothiazine). The arrays differ systematically in the distance between the redox-active metal complex and PTZ sites. They have been used in photophysical studies to provide insight into the distance dependence of electron transfer. (J. Am. Chem. Soc. 2004, 126, 14506-14514). This work describes the synthesis, purification, and characterization of the oligoproline arrays, including a general procedure for the synthesis of related arrays.
[Show abstract][Hide abstract] ABSTRACT: Three diastereomeric second-generation (G2) dendrons were prepared by using (2S,4S)-, (2S,4R)-, and (2R,4S)-4-aminoprolines on the multigram scale with highly optimized and fully reproducible solution-phase methods. The peripheral 4-aminoproline branching units of all the dendrons have the 2S,4S configuration throughout, whereas those units at the focal point have the 2S,4S, 2S,4R, and 2R,4S configurations. These latter configurations led to the dendrons being named (2S,4S)-1, (2S,4R)-1, and (2R,4S)-1, respectively. The 4-aminoproline derivatives used in this study are new, although many closely related compounds exist. Their syntheses were optimized. The dendron assembly involved amide coupling, the efficiency of which was also optimized by employing the following well-known reagents: EDC/HOBt, DCC/HOSu, TBTA/HOBt, TBTU/HOBt, BOP/HOBt, pentafluorophenol, and PyBOP/HOBt. It was found that the use of PyBOP is by far the best for dendrons (2S,4S)-1 and (2R,4S)-1, and pentafluorophenol active ester is best for (2S,4R)-1. Because of their multigram scale, all couplings were done in solution instead of by solid-phase procedures. Purifications were, nevertheless, easy. The optical purities of the key intermediates as well as the three G2 dendrons were analyzed by chiral HPLC analysis. These novel, diastereomeric second-generation dendrons have a rather compact and conformationally highly rigid structure that makes them interesting candidates for applications, for example, in the field of dendronized polymers and in organocatalysis.
Chemistry - An Asian Journal 12/2007; 2(12):1540-8. DOI:10.1002/asia.200700207 · 4.59 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Polymer bottlebrushes with monodisperse oligoproline side chains were efficiently synthesized, and the conformation of the peptide side chains in different solvents was investigated. Polymers with number-average degrees of polymerization (DPn) of 89 and 366 were obtained by polymerization of the macromonomer in iPrOH/MeCN (1:1) and hexafluoroisopropanol, respectively. Circular dichroism (CD) spectra of the bottlebrush polymers in the neutral and charged states reveal that the oligoproline side chains attain stable polyproline II (PPII) helical conformations not only in aqueous solution, but also in aliphatic alcohol solutions. Dense attachment of oligopeptides onto a linear polymer chain did not lead to an increase in helix content. The possible effects of the main-chain length on the conformational stability were examined. The switching between the polyproline I (PPI) and PPII helical conformations for the oligoproline side chains in aliphatic alcohol solutions is believed to be inhibited by the overcrowded structure in the polymer bottlebrushes.
[Show abstract][Hide abstract] ABSTRACT: Aryl halides can be easily transformed in a one-pot procedure into 4-aryl-1,2,3-triazoles with palladium/copper-catalyzed Sonogashira-click reaction sequence, using trimethylsilylacetylene as acetylene surrogate.
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.