Syntheses of potential spin probes for biomembranes - Tempo and proxyl nitroxides of lithocholic acid

Article abstract of DOI:10.1016/S0040-4020(01)92284-7

The synthesis of a steroidal spin label 10 containing a tempo nitroxide group in the side chain of lithocholic acid 1 is reported. This is the first report of a tempo nitroxide in a steroidal side chain. The methodology involved a Wittig condensation between the steroidal phosphonium ylide 7 and tempone 9. The synthesis of a proxyl nitroxide 16 with the proxyl group in the side chain of 1 is also described. A mild oxidation of 16 to the corresponding 3-keto spin label 17 in high yield is also achieved.