Abstract:The role of vitamin A and its metabolites in the life processes starting with the historical background and its up to date information is discussed in the introduction. Also the role of 11Z-retinal in vision and retinoic acid in the biological processes is elucidated. The essential role of isotopically enriched systems in the progress of vision research, nutrition research etc. is discussed. In part B industrial commercial syntheses of vitamin A by the two leading companies Hoffmann-La Roche (now DSM) and BASF are discussed. The knowledge obtained via these pioneering syntheses has been essential for the further synthetic efforts in vitamin A field by other scientific groups. The rest of the paper is devoted to the synthetic efforts of the Leiden group that gives an access to the preparation of site directed high level isotope enrichment in retinals. First the synthesis of the retinals with deuterium incorporation in the conjugated side chain is reviewed. Then, 13 C-labeled retinals are discussed. This is followed by the discussion of a convergent synthetic scheme that allows a rational access to prepare any isotopomer of retinals. The schemes that provide access to prepare any possible isotope enriched chemically modified systems are discussed. Finally, nor-retinals and bridged retinals that give access to a whole (as yet incomplete) library of possible isotopomers are reviewed.

3‐Cyano‐4‐methyl‐1H‐pyrrole (1) was prepared by a new Wittig procedure from simple, commercially available starting materials in four steps with an overall yield of 39 %. Similarly, [1‐15N]‐3‐cyano‐4‐methyl‐1H‐pyrrole (1a) was prepared starting from [15N]‐phthalimide. In this synthesis, Wittig coupling was used to form the central C–C bond of intermediate 6, which has nitrile and methyl substituents. Upon deprotection and cyclization pyrrole 1 is obtained directly in one pot. This scheme also allows stable isotope incorporation at any position or a combination of positions. 3‐Cyano‐4‐methyl‐1H‐pyrrole was converted into the novel 1‐benzyl‐3‐cyano‐4‐methylpyrrole and the novel 4‐methyl‐1H‐pyrrole‐3‐aldehyde. It is clear that this novel Wittig procedure has a wide scope that will allow the easy preparation of many new pyrrole systems.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Proteins and peptides play a preeminent role in the processes of living cells. The only way to study structure-function relationships of a protein at the atomic level without any perturbation is by using non-invasive isotope sensitive techniques with site-directed stable isotope incorporation at a predetermined amino acid residue in the protein chain. The method can be extended to study the protein chain tagged with stable isotope enriched amino acid residues at any position or combinations of positions in the system. In order to access these studies synthetic methods to prepare any possible isotopologue and isotopomer of the 22 genetically encoded amino acids have to be available. In this paper the synthetic schemes and the stable isotope enriched building blocks that are available via commercially available stable isotope enriched starting materials are described.

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Ammonium acetate / acetic acid‐catalyzed Knoevenagel reactions are studied.