Moshe Portnoy

A Unique Paradigm for a Turn-ON Near-Infrared Cyanine-Based Probe: Noninvasive Intravital Optical Imaging of Hydrogen Peroxide

The development of highly sensitive fluorescent probes in combination with innovative optical techniques is a promising strategy for intravital noninvasive quantitative imaging. Cyanine fluorochromes belong to a superfamily of dyes that have attracted substantial attention in probe design for molecular imaging. We have developed a novel paradigm to introduce a Turn-ON mechanism in cyanine molecules, based on a distinctive change in their π-electrons system. Our new cyanine fluorochrome is synthesized through a simple two-step procedure and has an unprecedented high fluorescence quantum yield of 16% and large extinction coefficient of 52,000 M(-1)cm(-1). The synthetic strategy allows one to prepare probes for various analytes by introducing a specific triggering group on the probe molecule. The probe was equipped with a corresponding trigger and demonstrated efficient imaging of endogenous hydrogen peroxide, produced in an acute lipopolysaccharide-induced inflammation model in mice. This approach provides, for the first time, an available methodology to prepare modular molecular Turn-ON probes that can release an active cyanine fluorophore upon reaction with specific analyte.

Reductive dechlorination of aryl chlorides catalyzed by palladium complexes containing basic, chelating phosphines

Abstract Aryl chlorides undergo efficient, homogeneously catalyzed reductive dechlorination to the corresponding arenes using Pd(dippp) 2 as catalyst [dippp=1,3-bis(diisopropylphosphino) propane], which may be generated in situ from Pd(OAc) 2 and two equivalents of dippp. Two reducing systems are described: (a) sodium hydroxide in methanol; (b) sodium formate in alcohol or DMF. Base-sensitive functional groups (CHO, CN) do not survive the conditions of system (a), but remain unaffected during dechlorination with sodium formate. Various functional groups are tolerated, and high yields are obtained. The reaction rate is retarded by electron-donating substituents, indicating a rate-determining oxidative addition step. Reaction of the model complex (dippp)Pd(Ph)Cl with sodium formate in the presence of dippp leads to the formation of Pd(dippp) 2 and benzene. Dippp homologues are also effective ligands in the catalytic reaction, the reactivity order being dippp > dippb > dippe. Iso-Pr 3 P is only marginally effective. A mechanistic interpretation of these observations is given.

Formylation of aryl chlorides catalysed by a palladium complex

The complex (dippp)2Pd [dippp = 1,3-bis(di-isopropylphosphino)propane] is an efficient, unique catalyst for direct formylation of aryl chlorides to aldehydes with CO and sodium formate.