Selective C-Terminal Conjugation of Protease-Derived Native Peptides for Proteomic Measurements.

Bottom-up proteomic experiments often require selective conjugation or labeling of the N- and/or C-termini of peptides resulting from proteolytic digestion. For example, techniques based on surface fluorescence imaging are emerging as a promising route to high-throughput protein sequencing but require the generation of peptide surface arrays immobilized through single C-terminal point attachment while leaving the N-terminus free. While several robust approaches are available for selective N-terminal conjugation, it has proven to be much more challenging to implement methods for selective labeling or conjugation of the C-termini that can discriminate between the C-terminal carboxyl group and other carboxyl groups on aspartate and glutamate residues.

Synthesis of Semicrystalline Polyolefin Materials: Precision Methyl Branching via Stereoretentive Chain Walking.

We report the discovery of C-symmetric nickel catalysts capable of the regio- and isoselective polymerization of 1-butene to produce isotactic 4,2-poly(1-butene), a new semi-crystalline polyolefin. The catalyst exhibits enantioface selectivities as high as 84% and the resulting polymers display melting temperatures up to 86 °C. This system marks a rare example of preserving stereochemistry through a chain walking polymerization process.

Regiodivergent addition of phenols to allylic oxides.

The regiodivergent addition of substituted phenols to allylic oxides has been demonstrated using C2-symmetric palladium complexes. Complex phenol donors tyrosine, estradiol, and griseofulvin follow the predictive model.

Regiodivergent addition of phenols to allylic oxides: control of 1,2- and 1,4-additions for cyclitol synthesis.

Control of 1,2- and 1,4-addition of substituted phenols to allylic oxides is achieved by intercepting palladium π-allyl complexes. The interconversion of palladium complexes results in the total synthesis of MK 7607, cyathiformine B type, streptol, and a new cyclitol.

A Regioselective Synthesis of the Dephospho DIthiolene Protected Molybdopterin.

The molybdopterin (MPT) is a complex molecule, made out of three distinctly different components. A retrosynthetic analysis provides a possible route for its synthesis that utilizes the coupling of a diamine with an osone analog. A regioselective condensation of the diamine with an osone affords the dephospho MPT, which has been characterized by NMR and IR spectroscopies, as well as high-resolution mass spectrometry.