Tritium labelling of RAD001—a new rapamycin derivative

RAD0012, a new immunosuppressant, was labelled in its hydroxyethyl side chain as well as in the rapamycin skeleton using carrier-free lithium triethylborotritide and tributyltin tritide (TBTT), respectively. The tritium labelling of the rapamycin moiety followed Curran's strategy of intramolecular hydrogen transfer. Our studies demonstrated that base-free TBTT is essential for a successful reaction. Copyright © 2000 John Wiley & Sons, Ltd.