Dehydrophenylalanine (ΔPhe) was incorporated into an antibiotic peptide gramicidin S (GS) in place of D‐Phe4,4′ to prepare an unsaturated analog. Conformational analysis with 1H‐NMR indicated that the unsaturated analog has much the same backbone conformation as that of natural gramicidin S as shown by NOE experiments. Studies on temperature dependences and on the chemical shift differences showed that the hydrogen bonds between Val‐NH and Leu‐CO in the unsaturated analog are strengthened by the incorporation of ΔPhe4,4′. This resulted in the reinforcement of the β‐sheet structure which is the most important structural element for GS bioactivity. [ΔPhe4,4′]gramicidin S exhibited indeed very strong antimicrobial activities against Gram‐positive bacteria as well as the natural peptide.

The intramolecular neighboring group participation of the amino group of 7-aminocoumarin moiety to phenylboronic acid gave fluorescence intensity and spectral changes upon saccharide binding which could be used in fluorescence mapping of saccharides in biological cells.

Unsaturated gramicidin S analog, [ΔPhe4,4′]gramicidin S, was synthesized by conventional solution method in order to evaluate the role of the dehydrophenylalanine residues replacing d‐phenylalanine4,4′ in stabilizing the bioactive β‐shect conformation. The dehydrophenylalanine (ΔPhe) moiety was introduced by dehydroazlactonization of the β‐phenylserine residue. The [ΔPhe4,4′]gramicidin S prepared by this method showed very strong antimicrobial activities against Gram‐positive bacteria, but not against Gram‐negative ones. Several lines of spectroscopic evidence indicated that [ΔPhe4,4′] gramicidin S has a reinforced β‐sheet backbone conformation necessary for a full biological activity of gramicidin S. These results suggested that :α,β‐dehydrogenation of the amino acid residue in a cyclic peptide can stabilize the turn structure.

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Dye-sensitized photooxidations of allyltrimethylsilanes yield cis ene products predominantly in contrast to the highly stereoselective formation of trans ene products from carbon standards.