Synthesis of pentafluorosulfanyl (SF5) containing aromatic amino acids.

Herein, a series of aromatic pentafluorosulfanyl (SF5) containing amino acids are reported. A Negishi cross-coupling strategy utilising a catalyst system of Pd(dba)2 and SPhos afforded the aforementioned SF5 amino acids in yields between 32% and 42%. Two dipeptides utilising both the amine and carboxylic functionalities of the synthesised SF5 containing amino acids were prepared, demonstrating their compatibility with common amide/peptide coupling reagents and strategies.

Excited state dynamics of the isolated green fluorescent protein chromophore anion following UV excitation.

A combined frequency-, angle-, and time-resolved photoelectron spectroscopy study is used to unravel the excited state dynamics following UV excitation of the isolated anionic chromophore of the green fluorescent protein (GFP). The optically bright S3 state, which is populated for hv > 3.7 eV, is shown to decay predominantly by internal conversion to the S2 state that in turn autodetaches to the neutral ground state. For hv > 4.1 eV, a new and favorable autodetachment channel from the S2 state becomes available, which leads to the formation of the neutral in an excited state. The results indicate that the UV excited state dynamics of the GFP chromophore involve a number of strongly coupled excited states.

A direct method for the synthesis of orthogonally protected furyl- and thienyl- amino acids.

The synthesis of unnatural amino acids plays a key part in expanding the potential application of peptide-based drugs and in the total synthesis of peptide natural products. Herein, we report a direct method for the synthesis of orthogonally protected 5-membered heteroaromatic amino acids.

Novel fluorinated lipopeptides from Bacillus sp. CS93 via precursor-directed biosynthesis.

While attempting to improve production of fluoro-iturin A in Bacillus sp. CS93 new mono- and di-fluorinated fengycins were detected in culture supernatants by (19)F NMR and tandem mass spectrometry, after incubation of the bacterium with 3-fluoro-L-tyrosine. The fluorinated amino acid was presumably incorporated in place of one or both of the tyrosyl residues in fengycin. Investigations to generate additional new fluorinated derivatives were undertaken using commercially available fluorinated phenylalanines and 2-fluoro- and 2,3-difluoro-tyrosine that were synthesised by Negishi cross-coupling of iodoalanine and fluorinated bromo-phenols. The anti-fungal activity of the fluorinated lipopeptides was assayed against Trichophyton rubrum and found to be similar to that of the non-fluorinated metabolites.

Communication: Autodetachment versus internal conversion from the S1 state of the isolated GFP chromophore anion.

The anionic form of p-hydroxybenzylidene-2,3-dimethylimidazolinone (HBDI) has been extensively employed as a model of the chromophore of the green fluorescence protein. The bright S1 excited state HBDI(-) has a measured lifetime of 1.4 ps in the gas-phase and is dominated by two non-radiative decay mechanisms: internal conversion and autodetachment into the neutral continuum. Here, time-resolved photoelectron spectroscopy has been used to determine the yields of these two channels from which the lifetime for autodetachment was found to be ∼30 ps.