Hydrocarboxyl Radical as a Product of α-Alanine Ultraviolet Photolysis.

UV photodissociation of α-alanine was studied by parahydrogen matrix isolation infrared spectroscopy. The temporal behavior of Fourier transform infrared spectra revealed that UV irradiation at 213 nm yielded the HOCO radical as a direct photoproduct from the S2 excited state. The concentration of HOCO quickly approached a steady state due to secondary photodissociation of HOCO to produce CO2 + H or CO + OH. On the other hand, no photoproducts were detected by S1 excitation at 266 nm. Irradiation of fully deuterated α-alanine at 213 nm yielded ∼2 times more cis-DOCO radicals than the lower energy isomer trans-DOCO, indicating that the conformation of the hydroxyl group is fairly well-preserved upon photodissociation of α-alanine. The present study suggests that HOCO may be a good tracer species in the search for amino acids in interstellar space.

Synthesis and Activation of Bench-Stable 3a-Fluoropyrroloindolines as Latent Electrophiles for the Synthesis of C-2-Thiol-Substituted Tryptophans and C-3a-Substituted Pyrroloindolines.

Indole dearomatization of tryptophan represents a key approach in the synthesis of indole containing alkaloids. Although the reactivity of C-3a-bromo-, 3a-iodo-, and 3a-chloropyrroloindolines has been explored, the utility and reactivity of C-3a-fluoropyrroloindolines has remained untapped. Here we induce the C-F bond to undergo a Sn1-like reaction. We demonstrate the utility of 3a-fluoropyrroloindoline to access C-2-thiol-substituted tryptophans and C-3a-substituted pyrroloindolines under mild conditions in high yield. A range of Nα-protecting groups and free -COOH are well-tolerated.