Synthesis of [3‐ 13 C]‐, [4‐ 13 C]‐ and [11‐ 13 C]‐porphobilinogen

[4‐ 13 C]‐porphobilinogen 1a, [3‐ 13 C]‐porphobilinogen 1b and [11‐ 13 C]‐porphobilinogen 1c are prepared from [1‐ 13 C]‐3‐(tetrahydropyran‐2′‐yloxy)‐propionaldehyde 2a, methyl [4‐ 13 C]‐4‐nitrobutyrate 3b and [1‐ 13 C]‐isocyanoacetonitrile 5c, respectively. The building blocks 2, 3 and 5 can be prepared efficiently in any isotopomeric form. Via base‐catalyzed condensation of these building blocks porphobilinogen can be enriched with 13 C and 15 N stable isotopes at any position and combination of positions. Copyright © 2009 John Wiley & Sons, Ltd.