A full synthetic study of linear and cyclic thiophene oligoamides has been carried out. The combination of an ultrasonic technique to diminish the intramolecular backfolding of longer oligoamide chains, therefore enhancing the accessibility of the carboxylic acid, and T3P as coupling reagent led to shorter reaction time and higher yields for both linear and cyclic oligoamides. By controlling the degree of dilution, macrocyclic amides with different sizes can selectively be prepared. Different crystal structures of cyclic thiophene oligoamides were also analyzed.
The dipeptide isostere 5-aminothiophene carboxylic acid has been combined with L-phenylalanine moieties to provide linear and cyclic hybrid oligopeptides. A suitable protecting group strategy and appropriate coupling methods have been developed to guarantee a high degree of enantiopurity of the resulting amides. Cyclic tetraamides have been efficiently obtained by macrocyclization of the linear derivatives. In the case of racemized cyclization precursors, two diastereomeric macrocycles (S,S/R,R and meso) have been isolated. Their crystal structures show clear effects of the stereogenic centers on the ring conformations and molecular packing.
Not only many organic N-sulfinylamines [ I ] but also N-(trimethylsilyl)sulfinylamine[zl are known, the reactions of the latter being very similar to those of silyl pseudohalides. We have obtained bis(sulfinylamido)mercury(II) ( I ) as the first sulfinylamide of a metal by reaction of mercury(i1) fluoride with N-(trimethylsily1)sulfinylamine. The reaction proceeds quantitatively.Tetrahydrofuran is a particularly suitable solvent as ( I ) dissolves readily in it and can be recrystallized from it. 23 g of HgFz reacts with 27 g of (CH&SiNSO in 40-60 ml of boiling, stirred, dry T H F within 30 rnin in a strongly exothermic reaction. The amide ( I ) crystallizes as colorless needles, m.p. 128 "C (decomp.), but, if heating is too slow, decomposition sets in below the melting point. In contrast to most organic sulfinylamines, it is surprisingly stable to hydrolysis and alcoholysis. Compound ( I ) was identified by analysis and its mass spec-trumr31 [with reference to the isotope 202Hg: m / e = 326, Hg(NS0)2; 264, Hg(NS0); 202, Hg; 48, SO; 46, NS; 32, S]. The I R spectrum (Nujol) shows bands at 1250s, 1217s, 1078 s, 604 rn, 590 m, 561 m, 313 s, and 280 w cm-1.
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