Direct arylation of meso-formyl porphyrin.

Palladium-catalyzed direct arylation of meso-formyl Ni(II) porphyrin with aryl bromides provided ß-monoarylated meso-formyl porphyrins. In spite of the existence of the meso-formyl group, the reactions proceeded regioselectively at the ß-position adjacent to the formyl group. ß-Arylated formyl porphyrin was converted to a tetraline-fused porphyrin by reduction and subsequent acid-catalyzed cyclization and to a meso-meso vinylene-bridged diporphyrin by McMurry coupling (see scheme).

Differential (14)N/(15)N-Labeling of Peptides Using N-Terminal Charge Derivatization with a High-Proton Affinity for Straightforward de novo Peptide Sequencing.

While de novo peptide sequencing is essential in many situations, it remains a difficult task. This is because peptide fragmentation results in complicated and often incomplete product ion spectra. In a previous study, we demonstrated that N-terminal charge derivatization with 4-amidinobenzoic acid (Aba) resulted in improved peptide fragmentation under low-energy CID conditions. However, even with this derivatization, some ambiguity exists, due to difficulties in discriminating between N- and C-terminal fragments. In this study, to specifically identify b-ions from complex product ion spectra, the differential (14)N/(15)N-labeling of peptides was performed using Aba derivatization. (15)N-Labeled Aba was synthesized in the form of a succinimide ester. Peptides were derivatized individually with (14)N-Aba or (15)N-Aba and analyzed by ESI-MS/MS using a linear ion trap-Orbitrap hybrid FTMS system. The N-terminal fragments (i.e., b-ions) were then identified based on m/z differences arising from isotope labeling. By comparing the spectra between (14)N- and (15)N-Aba derivatized peptides, b-ions could be successfully identified based on the m/z shifts, which provided reliable sequencing results for all of the peptides examined in this study. The method developed in this study allows the easy and reliable de novo sequencing of peptides, which is useful in peptidomics and proteomics studies.

Improving peptide fragmentation by N-terminal derivatization with high proton affinity.

An improved method of de novo peptide sequencing based on mass spectrometry using novel N-terminal derivatization reagents with high proton affinity has been developed. The introduction of a positively charged group into the N-terminal amino group of a peptide is known to enhance the relative intensity of b-ions in product ion spectra, allowing the easy interpretation of the spectra. However, the physicochemical properties of charge derivatization reagents required for efficient fragmentation remain unclear. In this study, we prepared several derivatization reagents with high proton affinity, which are thought to be appropriate for peptide fragmentation under low-energy collision-induced dissociation (CID) conditions, and examined their usefulness in de novo peptide sequencing. Comparison of the effects on fragmentation among three derivatization reagents having a guanidino or an amidino moiety, which differ in proton affinity, clearly indicated that there was an optimal proton affinity for efficient fragmentation of peptides. Among reagents tested in this study, derivatization with 4-amidinobenzoic acid brought about the most effective fragmentation. This derivatization approach will offer a novel de novo peptide sequencing method under low-energy CID conditions.