The mechanism of photoinduced acylation of amines by N-acyl-5,7-dinitroindoline as determined by time-resolved infrared spectroscopy

[reaction: see text] The photochemistry of N-acyl-5,7-dinitroindoline (1) was studied in acetonitrile using nanosecond time-resolved infrared (TRIR) spectroscopy. Upon photolysis, two nearly but not completely overlapping sets of transient IR bands are observed that are assigned to two non-interconvertible conformers of mixed acetic nitronic anhydride 7. While syn-7 reverts rapidly to 1, anti-7 is long-lived and is able to acylate amines. Results of density functional theory calculations support conclusions based on experimental TRIR data.     

Sequentially photocleavable protecting groups in solid-phase synthesis

[reaction: see text] A sequential solid-phase peptide synthesis was developed using both photolabile linker and protecting groups. The chromatic sequential lability between a tert-butyl ketone-derived linker (sensitive to irradiation at 305 nm) and a nitroveratryloxycarbonyl (NVOC) group (sensitive at 360 nm) was exploited to prepare Leu-Enkephalin in a 55% overall yield. This new strategy allows the preparation of peptides in essentially neutral medium, by avoiding the use of common deprotection reagents such as trifluoroacetic acid or piperidine.     

Bis(o-nitrophenyl)ethanediol: A practical photolabile protecting group for ketones and aldehydes

The ketals of bis(o-nitrophenyl)ethanediol and ketones or aldehydes are smoothly deprotected in neutral conditions by irradiation with 350 nm light. The chemical stability in basic, acidic, and oxidizing media makes this form of protection orthogonal to classical protecting groups. Both racemic and enantiopure forms are readily available in two steps from inexpensive starting materials.