RESUMO
A simple synthesis method of solanidane alkaloids from common steroidal sapogenins was developed. Previously described multi-step transformations of tigogenin to demissidine (8-12â steps) were shortened to four steps only. The key-step of the present synthesis was the epimerization at C25 of the lactam intermediate. Different approaches to this reaction, i. e., a classical one via enolate, and a chemoselective umpolung transformation, were thoroughly investigated. The epimerization step is unnecessary if the starting sapogenin has the same configuration at C25 as the target alkaloid because the configuration at C25 (either R or S) remains intact throughout the synthesis. Thus, the related solanidane alkaloids, 12ß-hydroxy-25-epi-demissidine and 5-epi-demissidine, were synthesized in the three-step procedure with retention of configuration at this stereogenic center from rockogenin (25R-5α-sapogenin) or sarsasapogenin (25S-5ß-sapogenin), respectively.
RESUMO
A new fluorescence probe based on [5]helicene derivative (MT) was designed and synthesized. The chemical structure of the probe was fully characterized by NMR, mass spectrometry and X-ray crystallography. MT which is the combination of thioamide[5]helicene with Schiff base-thiophene moiety, exhibited a high selectivity to detect Hg2+ through irreversible desulfurization reaction with "TurnON" fluorescence response and large Stokes shift of 110 nm in aqueous methanol solution. The detection limit of MT was 1.2 ppb (6.0 × 10-3 µM), which is lower than the limit of Hg2+ level in drinking water, as specified by WHO (6.0 ppb) and U.S. EPA (2.0 ppb). The Hg2+ detection range of the probe was 0.07-1.6 µM with good linearity. Under UV irradiation, MT possessed the capability to detect Hg2+ in diverse context of real samples, including drinking and sea waters, vegetable tissue and brain tumor cell. In addition, MT could be used as a paper test strip for monitoring and screening of Hg2+ contamination in environment.
