Synthesis, conformation, and immunosuppressive activities of three analogs of cyclosporin A modified in the 1-position

Abstract

The syntheses of three new cyclosporin A (CsA) analogues that contain novel MeBmt derivatives in the 1-position are described. The MeBmt analogue that contains an additional methyl group on C4, (2S,3R,6E)-4,4-dimethyl-3-hydroxy-2-(N-methylamino)-6-octenoic acid (MeBm2t), was synthesized in four steps beginning with the reaction of Pmz-Sar-OtBu with (4E)-2,2-dimethyl-4-hexenal. The C4 desmethyl analogue of MeBmt, (2S,3R,6E)-3-hydroxy-2-(N-methylamino)-6-octenoic acid (MeBth), was synthesized in nine steps by a route based on the Sharpless chiral epoxidation procedure. The alkynyl derivative of MeBmt, (2S,3R,4R)-4-methyl-3-hydroxy-2-(N-methylamino)-6-octynoic acid (MeByt), was synthesized by a modification of the procedure described by Tung et al. for the synthesis of MeBmt. Each MeBmt analogue was protected as the N,O-acetonide and coupled with the hexapeptide Abu-Sar-MeLeu-Val-MeLeu-Ala-OBzl. The resulting heptapeptide was deprotected and coupled with Fmoc-D-Ala-MeLeu-MeLeu-MeVal-OH. The resulting undecapeptides were deprotected and cyclized to give the corresponding CsA analogues. Conformational analysis by 1D and 2D NMR methods was carried out for each analogue in chloroform, and the results are compared with the corresponding solution conformations of CsA and dihydrocyclosporin. The immunosuppressive activities of each analogue, determined in concanavalin A stimulated thymocytes, are lower than obtained for CsA. The results establish the important effect the methyl group and the double bond in MeBmt have on the solution conformation of the 1-position residue in CsA and on immunosuppressive activity.

Macrocyclic N-Methylated Cyclic Peptides and Depsipeptides

“…From this investigation, it was clearly shown that immunosuppressive activity was influenced by a large part of the overall Cs molecule and only a few variations could be installed to increase the activity. A study regarding the CsA 51 conformation in solution has been performed [47]. It was found that the insertion of a polar group always caused the activity to be diminished [46].…”

Crystal structures of cyclophilin A complexed with cyclosporin A and N-methyl-4-[(E)-2-butenyl]-4,4-dimethylthreonine cyclosporin A

“…CsA was kindly provided by Sandoz Pharma LTD, Switzerland. MeBm 2 tl-CsA was synthesized as described [49]. Co-crystals of the CyPA-CsA complex were grown by a two-step procedure: (1) mixing the 16mgml-1 CyPA protein solution from the purification with 10 mM CsA/ethanol in a molecular ratio of 1:2 overnight and (2) crystallizing 13mgml-1 of the complex by dialysis against a buffer containing 20mM Tris-base, 2mM…”

Calcineurin inhibitors: status quo and perspectives

“…Unfortunately, in cells both compounds inhibit the PPIase activity of cyclophilins at the nanomolar concentration range and are therefore unsuitable as a monospecific calcineurin inhibitor. Moreover, modifications of residues in the cyclophilin binding region (e.g., MeBmt at position 1) by substitution or elongation of the side chain alter only the cyclophilin inhibition, but impair the immunosuppressive potency only marginally, as observed for wMeBm 2 t 1 x-CsA, wMeBth 1 x-CsA, wMeByt 1 x-CsA and voclosporin (ISA247) (53,54). A completely new regulation mechanism of CsA inhibitory potency was realized with a CsA derivative containing a biotin moiety connected by an azobenzene tether (55).…”