Regioselective synthesis of methyl 5-(N-Boc-cycloaminyl)-1,2-oxazole-4-carboxylates as new amino acid-like building blocks.

A convenient and efficient synthesis of novel achiral and chiral heterocyclic amino acid-like building blocks was developed. Regioisomeric methyl 5-(N-Boc-cycloaminyl)-1,2-oxazole-4-carboxylates were prepared by the reaction of ß-enamino ketoesters (including azetidine, pyrrolidine or piperidine enamines) with hydroxylamine hydrochloride. Unambiguous structural assignments were based on chiral HPLC analysis, 1H, 13C, and 15N NMR spectroscopy, HRMS, and single-crystal X-ray diffraction data.

Synthesis and Characterization of Novel Methyl (3)5-(N-Boc-piperidinyl)-1H-pyrazole-4-carboxylates.

Series of methyl 3- and 5-(N-Boc-piperidinyl)-1H-pyrazole-4-carboxylates were developed and regioselectively synthesized as novel heterocyclic amino acids in their N-Boc protected ester form for achiral and chiral building blocks. In the first stage of the synthesis, piperidine-4-carboxylic and (R)- and (S)-piperidine-3-carboxylic acids were converted to the corresponding ß-keto esters, which were then treated with N,N-dimethylformamide dimethyl acetal. The subsequent reaction of ß-enamine diketones with various N-mono-substituted hydrazines afforded the target 5-(N-Boc-piperidinyl)-1H-pyrazole-4-carboxylates as major products, and tautomeric NH-pyrazoles prepared from hydrazine hydrate were further N-alkylated with alkyl halides to give 3-(N-Boc-piperidinyl)-1H-pyrazole-4-carboxylates. The structures of the novel heterocyclic compounds were confirmed by 1H-, 13C-, and 15N-NMR spectroscopy and HRMS investigation.

Colorimetric Cyanide Chemosensor Based on 1',3,3',4-Tetrahydrospiro[chromene-2,2'-indole].

A new class of chemosensors based on the 1',3,3',4-tetrahydrospiro[chromene-2,2'-indole] ring system, which detects cyanide with high specificity, is described. These chemosensors show a distinct color change when treated with cyanide in acetonitrile solution buffered with sodium phosphate, and this procedure is not affected by the presence of other common anions. The chemisensors exhibit high sensitivity to low concentrations of cyanide, meeting the European Union water quality control criterion of sensitivity below 0.05 mg L(-1), and show a very fast response within tens of seconds. The mechanism for detection is rationalized by the nucleophilic substitution of the phenolic oxygen atom at the indoline C-2 atom by the cyanide anion to form a stable indolylnitrile adduct and to generate the colored 4-nitrophenolate chromophore. These chemosensors can be synthesized by a simple procedure from commercially available starting materials.