Development of a temporary marker for peptidesElectronic supplementary information (ESI) available: IR, UV, 1H NMR and 13C NMR spectra of compounds 2a–i, 3b–h, 4b–h, 5, 6c and h, 7h, 8–12, 13c and h, and 14. See http://www.rsc.org/suppdata/ob/b2/b212470j/