Bioorganic & Medicinal Chemistry Letters, Vol. 4, No. 13. pp. 1581-1584. 1994 Copyright (D 1994 Elsevim Science Ltd Printed in &eat Britain. All rights reserved 0960-894x194 $7.00+0.00 0960-894x(94)00198-7 Synthesis And Study Of A Non Macrocyclic FK506 Derivative. Simon J. Teague*, Martin E. Cooper, David K. Donald and Mark Furber Fisons plc, Pharmaceutical8 Division, Bakewell Road, Loughborough, LEll ORH, U.K. Abstract: The affinity of a non macmcyclic analogue of FKSO6 for the immunophilin FKBPl2 was determined. The aftinity of this analogue/FKBPlZ complex for calcineurin was studied. FK506, a macrocyclic natural product, has received intensive investigation because of its powerful immunosuppressive properties and the insights it provides into cytoplasmic signal transductiont IX506 binds tightly to the ub4uitous cytosolic protein FKBP12? and the resulting bimolecular complex then inhibit8 the cahnodulin-dependent protein phosphatase PP2B (calcineurin). 3 This phosphatase is also inhibited by the complex formed between the structurally unrelated cyclic undecapeptide cyclosporin and cyclophilin.4 Inhibition of calcineurin results in failure to dephosphorylate the nuclear transcription factor of activated T-cells (NFAT) an< hence to disruption of IL-2 gene transcription and ultimately to down regulation of the T-cell component of the immune response. Inapreviouspaperjwe examined the affinity of the excised big domain of FK506 for the immunophilin FKBP12. This study allowed us to determine the affiity of the binding region in the absence of the constraints imposed upon it by the macrocyclic framework Thus when those part8 of the macrocycle which are not in contact with the immunophilin were removed, a SO-fold reduction in affinity was observed. In a continuation of this study we wished to de&rmine the contribution of macrocyclii constraints to the affmity of the FK506/FKBP12 complex for calcinetuin.6 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA FK-606 8. SLB606 Present understanding of the binding of the FK5O6/FKBP12 complex to calcineurin suggests that a composite surface is recognised. This surface consists of key residues of FKBPl2 (Gly 8g, Ile go and Arg 42)7 combined with lipophilic interactions contributed by the C15C23 region of FK506.8 These considerations led us to choose to cleave FKSo6 across the C23-C24 bond. It was anticipated that this would leave the key section of FK506 1581