Synthesis of Selectively 13C‐Labelled Bilin Compounds

Abstract

AbstractA series of open‐chain tetrapyrroles, each carrying one or more 13C‐labels in its three ring‐bridging methine groups, were synthesized. These compounds – [5‐, [10‐, and [15‐13C]‐phycocyanobilins (PCB), [10‐13C]‐phytochromobilin, and [10,15‐13C2]‐PCB – were each obtained by a convergent route, starting with the four pyrrole building blocks, with the initial formation of the left and the right halves of the tetrapyrrole separately, followed by a final condensation of the two dipyrrole units to yield the target bilin compound. The 13C‐labels were all inserted as C1‐ or C2‐units prior to the appropriate condensation. The substitution pattern of these bilins on ring A (ethylidene substituent at position 3) allows covalent attachment to the apoprotein of the plant photoreceptor phytochrome. The isotope shift produced by insertion of a 13C‐isotope is demonstrated in the FT‐IR spectra of phytochrome‐incorporated [10‐13C]‐phytochromobilin. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)