Four rhodamine 6G-based chemosensors (H
3
L1–H
3
L4) are designed for selective detection
of Al3+ ion. They are characterized using various spectroscopic
techniques and X-ray crystallography. All absorption and emission
spectral studies have been performed in 10 mM N-(2-hydroxyethyl)piperazine-N′-ethanesulfonic acid (HEPES) buffer solution at
pH 7.4 in H2O/MeOH (9:1, v/v) at 25 °C. In absorption
spectra, chemosensors exhibit an intense band around 530 nm in the
presence of Al3+ ion. Chemosensors (H
3
L1–H
3
L4) are nonfluorescent when excited around
490 nm. The presence of Al3+ ion enhances the emission
intensity (555 nm) many times. The formation of complexes 1–4 is established with the aid of different spectroscopic
techniques. The limit of detection value obtained in the nanomolar
range confirms the high sensitivity of the probes toward Al3+ ion. It has been observed that the presence of aliphatic spacers
in the diamine part and different halogen substituents in the salicylaldehyde
part strongly influences the selectivity of the chemosensors toward
Al3+ ion. The propensity of the chemosensors to identify
intracellular Al3+ ions in triple-negative human breast
cancer cell line MDA-MB-468 by fluorescence imaging is also examined
in this study.
A new approach to carbasugars in enantiomerically pure form is reported. The key step involves ringclosing metathesis of dienols 6 derived from a (R)-(+)-glyceraldehyde derivative 4 to form the substituted cyclopentenol 9 and cyclohexenol 34a. Stereocontrolled addition of hydroxyl groups followed by conversion of the ketal unit to hydroxymethyl group in these intermediates led to carbapentoses and -hexoses. Stereoselectivity during introduction of hydroxyl groups arises through the steric hindrance posed by the allylic substituents. A remarkable feature of the present approach is the accessibility of both D-and L-series of carbapentoses as illustrated by the synthesis of β-D-and β-L-carbaribofuranoses 17 and 20, respectively. Carba-R-D-ribofuranose 25, the biosynthetic intermediate to the antibiotic aristeromycin, has also been synthesized from the same cyclopentenol 9. Functional group manipulation in the cyclopentenol 9a also enabled access to carbaarabinofuranose 32. The present synthetic strategy can be extended for the synthesis of carbahexopyranose, as illustrated by the synthesis of carba-β-Lgulopyranose 40b.
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