Syntheses and evaluation of the bioluminescent activity of (S)-Cypridina luciferin and its analogs

Cypridina luciferin is the substrate in the bioluminescence of a luminous ostracod Cypridina (Vargula) hilgendorfii. Cypridina luciferin contains a chiral center in the sec-butyl moiety. Here, we report a convenient method for the preparation of (S)-Cypridina luciferin by the condensation of (S)-1,1-diethoxy-3-methylpentan-2-one with ethioluciferin. The light yield of the synthesized (S)-luciferin in the presence of Cypridina luciferase was about 1.7 times as active as that of racemic form. Furthermore, several luciferin analogs prepared by the same condensation with different α-ketoacetal derivatives showed moderate light yield with Cypridina luciferase. These readily available Cypridina luciferin and analogs are applicable to the bioluminescent detection of Cypridina luciferase.