A highly selective fluorescent probe for the intracellular measurement of magnesium ion.

Magnesium ion (Mg+2) plays an important role in various biological processes. All the commercial indicators available share a common drawback, i.e., they have a higher affinity towards calcium ions (Ca+2) than Mg+2. In this study, we reported a new robust green fluorescent indicator, Mag-520, for detection of Mg+2 in live cells. Our results showed that Mag-520 has 10 fold higher affinity towards Mg+2 than Ca+2, while mag-fluo-4 has less than 0.5 fold affinity to Mg+2 than Ca+2 under the same conditions using flow cytometry and fluorescence microscopy. The results demonstrated that Mag-520 provides a better tool to measure Mg+2 with less interference from Ca+2.

Studies toward the Total Synthesis of Nogalamycin: Construction of the Complete ABCDEF-Ring System via a Convergent Hauser Annulation.

The convergent synthesis of the complete ABCDEF-ring system within nogalamycin, an anthracycline natural product, was studied. The pivotal Hauser annulation for the anthraquinone core construction was achieved by the fusion of two highly functionalized segments: a cyanophthalide (the AB-ring segment) and a tricyclic quinone monoketal (the DEF-ring segment). Key transformations toward the AB-ring segment include an enantioselective enolate α-hydroxylation, a diastereoselective hydroboration-oxidation, and a directed aromatic lithiation-formylation. To prepare the DEF-ring segment for annulation, a mild dearomatization of the F-ring phenol group by (diacetoxyiodo)benzene (PIDA) was employed.

Construction of the DEF-Benzoxocin Ring System of Nogalamycin and Menogaril via a Reductive Heck Cyclization.

Construction of the DEF-ring system of nogalamycin and menogaril has been achieved with a novel reductive Heck cyclization approach. Our strategy exploited the stereoelectronic preferences dictated by the anomeric effect for introduction of an O-glycosidic bond in order to direct the introduction of a bridging C-glycosidic bond with the desired stereochemistry. Our strategy relied upon a stereoselective O-aryl glycosylation reaction and a highly efficient selenoxide elimination to provide the key substrate for study of the reductive Heck cyclization reaction. The cyclization proceeded smoothly under the optimized conditions, in a yield comparable to that achieved in our previously reported model study.

Fluorescent real-time quantitative measurements of intracellular peroxynitrite generation and inhibition.

Peroxynitrite (ONOO-), a strong oxidant species, is produced by the reaction of nitric oxide (NO) and superoxide (O2.-) radicals. It plays an important role as a biological regulator in numbers of physiological and pathological processes. In this study, we developed fluorescence-based real-time quantitative measurements to detect intracellular ONOO-. The probe DAX-J2 PON Green showed high selectivity toward ONOO- over other competing species, and has been successfully applied in microplate reader and flow cytometer to quantitatively measure endogenous ONOO- production. Moreover, the results demonstrated the inhibitory effects of curcumin on intracellular ONOO- generation.

A novel Ca2+ indicator for long-term tracking of intracellular calcium flux.

The major drawback of using Fluo-4 AM is that it requires an organic anion transporter inhibitor, such as probenecid, to prevent leakage. This can hinder the studies that require extended monitoring time and longer cellular retention. To address the issue, a novel Ca2+ indicator, Calbryte 520 AM, was developed. We compared the performance of Fluo-4 AM and Calbryte 520 AM following prolonged incubation periods after cell loading. Cells loaded with Calbryte 520 AM retained the dye for up to 24 h while exhibiting significant fluorescence brightness and superior Fmax/F0 ratios (Fmax: fluorescence intensity upon stimulation; F0: intensity before stimulation). It demonstrated that the longer retention of Calbryte 520 AM can be exploited to accommodate for the extended time required when monitoring calcium dynamics.

Selective dendritic fluorescent sensors for Zn(II).

A series of dendritic 8-hydroxyquinoline (8-HQ) and 5-dialkyl(aryl)aminomethyl-8-HQ derivatives were synthesized and their fluoroionophoric properties toward representative alkali, alkaline earth, group IIIA and transition metal ions were investigated. Among the selected ions, Zn(II) enhanced the fluorescence of N-di-(methoxycarbonylethyl)aminoethyl-3-[4-(8-hydroxyquinolin-5-ylmethyl)piperazin-1-yl]-propanoic amide] (7) by 31-fold, while Al(III) caused enhancement to some extent. The absence of any significant fluorescence enhancement by the other ions examined renders 7a highly useful Zn(II)-selective fluorescent sensor.

Synthesis of 5-dialkyl(aryl)aminomethyl-8-hydroxyquinoline dansylates as selective fluorescent sensors for Fe3+.

A series of 5-dialkyl(aryl)aminomethyl-8-hydroxyquinoline dansylates were synthesized and their fluoroionophoric properties toward representative alkali ions, alkaline earth ions and transition metal ions were investigated. Among the selected ions, Fe3+ caused considerable quenching of the fluorescence, while Cr3+ caused quenching to some extent. The absence of any significant fluorescence quenching effects of the other ions examined, especially Fe2+, renders these compounds highly useful Fe3+-selective fluorescent sensors.

A model study for constructing the DEF-benzoxocin ring system of menogaril and nogalamycin via a reductive Heck cyclization.

A novel reductive Heck cyclization approach was developed in order to construct a model DEF-benzoxocin ring system that is present in nogalamycin, menogaril, and related anthracycline antitumor antibiotics.