Cationic oligonucleotide-peptide conjugates with aggregating properties enter efficiently into cells while maintaining hybridization properties and enzymatic recognition

Oligonucleotide delivery is a crucial issue for therapeutical purposes and is often addressed by conjugation to short cationic peptides although with controversial results. To further examine this mechanism, a 15-mer anionic oligonucleotide was conjugated to a cationic peptide in order to obtain a diblock compound with an overall positive charge with aggregation properties. These microaggregates were efficiently internalized in cells via the expeditious pathway used by commercial gene delivery systems. Moreover, stability of the duplex formed with the complementary sequence increased without inhibiting oligonucleotide enzyme recognition as shown by the properties of the conjugate to prime chain elongation by Taq DNA polymerase in a linear amplification/sequencing process.     

Modular Oxime Formation by a trans-AT Polyketide Synthase

Modular trans-acyltransferase polyketide synthases (trans-AT PKSs) are enzymatic assembly lines that biosynthesize complex polyketide natural products. Relative to their better studied cis-AT counterparts, the trans-AT PKSs introduce remarkable chemical diversity into their polyketide products. A notable example is the lobatamide A PKS, which incorporates a methylated oxime. Here we demonstrate biochemically that this functionality is installed on-line by an unusual oxygenase-containing bimodule. Furthermore, analysis of the oxygenase crystal structure coupled with site-directed mutagenesis allows us to propose a model for catalysis, as well as identifying key protein-protein interactions that support this chemistry. Overall, our work adds oxime-forming machinery to the biomolecular toolbox available for trans-AT PKS engineering, opening the way to introducing such masked aldehyde functionalities into diverse polyketides.     

Denitration of nitroaromatic compounds by arylnitrile radical cations

Substituted nitrobenzenes react with substituted benzonitrile radical cations in an ion trap mass spectrometer by a novel ion/molecule reaction involving NO2 elimination. Formation of an arylated nitrile, Ar1+N identical to CAr2 (where Ar1, Ar2 = aryl), is indicated by collision induced dissociation and comparison with the behavior of the authentic ion. Ab initio calculations (MP2/6-31G*/ /HF/6-31G*) show the reaction of the unsubstituted compounds (Ar1, Ar2 = phenyl) to be exothermic by 48 kcal/mol, consistent with the experimental observation that the reaction rate decreases as the collision energy is increased. Electron withdrawing and donating substituents on either the ionic or the neutral reagent have little effect on the relative amount of product observed, pointing to a radical mechanism. Related denitration reactions were found to occur, between nitrobenzene and its radical cation and between phenylisonitrile and ionized nitrobenzene. These reactions are suggested to yield Ar1+N(= O)OAr2 and Ar2+N identical to CAr1, respectively. The denitration reaction was applied to trinitrotoluene (TNT) as a possible diagnostic reaction for the presence of nitroaromatic explosives.