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 S 2 excited state. The concentration of HOCO quickly approached a steady state due to secondary photodissociation of HOCO to produce CO 2 + H or CO + OH. On the other hand, no photoproducts were detected by S 1 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.
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 N
α-protecting groups and free -COOH are well-tolerated.
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