Synthesis and characterization of all‐E (12,12′‐¹³C₂)‐, (13,13′‐¹³C₂)‐, (14,14′‐¹³C₂)‐, (15,15′‐¹³C₂)‐ and (20,20′‐¹³C₂)astaxanthin

Abstract

Abstract The all‐ E isomers of (12,12′‐ 13 C 2 )‐, (13,13′‐ 13 C 2 )‐, (14,14′‐ 13 C 2 )‐, (15,15′‐ 13 C 2 )‐ and (20,20′‐ 13 C 2 )astaxanthin were prepared by total synthesis starting from commercially available 99% 13 C‐enriched acetonitrile, acetic acid and methyl iodide. The astaxanthins were obtained in high purity and with high isotope incorporation (> 99% for every position). For this synthesis, the C 15 + C 10 + C 15 strategy was used. The central C 10 ‐synthon, 2,7‐dimethylocta‐2,4,6‐triene‐1,8‐dial, was symmetrically dilabelled at any position using two new synthetic schemes. The 13 C 2 ‐enriched C 10 ‐dialdehydes were then converted in one step to the 13 C 2 ‐enriched astaxanthins.