Suggested Reaction 1.14.16.-

Left

20-Hydroxy-3-oxopregn-4-en-21-al
+6,7-Dihydrobiopterin
+H2O

Right

(S)-20-Hydroxypregn-4-en-3-one
+2-Amino-6-(1,2-dihydroxypropyl)-5,6,7,8-tetrahydoro-4(1H)- pteridinone
+O2

[BiSSCat | GREP ]