Sanglifehrin−Cyclophilin Interaction:  Degradation Work, Synthetic Macrocyclic Analogues, X-ray Crystal Structure, and Binding Data

Abstract

Sanglifehrin A (SFA) is a novel immunosuppressive natural product isolated from Streptomyces sp. A92-308110. SFA has a very strong affinity for cyclophilin A (IC(50) = 6.9 +/- 0.9 nM) but is structurally different from cyclosporin A (CsA) and exerts its immunosuppressive activity via a novel mechanism. SFA has a complex molecular structure consisting of a 22-membered macrocycle, bearing in position 23 a nine-carbon tether terminated by a highly substituted spirobicyclic moiety. Selective oxidative cleavage of the C(26)=C(27) exocyclic double bond affords the spirolactam containing fragment 1 and macrolide 2. The affinity of 2 for cyclophilin (IC(50) = 29 +/- 2.1 nM) is essentially identical to SFA, which indicates that the interaction between SFA and cyclophilin A is mediated exclusively by the macrocyclic portion of the molecule. This observation was confirmed by the X-ray crystal structure resolved at 2.1 A of cyclophilin A complexed to macrolide 16, a close analogue of 2. The X-ray crystal structure showed that macrolide 16 binds to the same deep hydrophobic pocket of cyclophilin A as CsA. Additional valuable details of the structure-activity relationship were obtained by two different chemical approaches: (1) degradation work on macrolide 2 or (2) synthesis of a library of macrolide analogues using the ring-closing metathesis reaction as the key step. Altogether, it appears that the complex macrocyclic fragment of SFA is a highly optimized combination of multiple functionalities including an (E,E)-diene, a short polypropionate fragment, and an unusual tripeptide unit, which together provide an extremely strong affinity for cyclophilin A.

Primary Identification, Biochemical Characterization, and Immunologic Properties of the Allergenic Pollen Cyclophilin Cat r 1

“…Protein Data Bank revealed that the overall fold is most closely related to the human (1NMK) and the Plasmodium (1QNH) Cyp structures (47)(48)(49). The biggest difference from the human structure is the presence of additional residues that are found in the plant and parasite species after the first ␣-helix (Fig.…”

Preclinical Characterization of Naturally Occurring Polyketide Cyclophilin Inhibitors from the Sanglifehrin Family

“…The crystal structures of SfA and a semisynthetic derivative bound to CypA have been published (26) and reveal that they both bind to the same active site as CsA. SfA analogues devoid of immunosuppressive properties have been synthesized (44), indicating an opportunity for the design of nonimmunosuppressive Cyp inhibitors for potential use in HCV therapy.…”

Discovery of Novel Small Molecule Anti-HCV Agents via the CypA Inhibitory Mechanism Using O-Acylation-Directed Lead Optimization

“…Except for the functions mentioned above, CypA also plays a critical part in the replication of various kinds of viruses, such as human immunodeficiency virus type 1 (HIV-1), influenza virus, HCV, vesicular stomatitis virus (VSV), vaccinia virus and human papilloma virus (HPV) [10,11]. On account of the importance of CypA in the regulation of numerous biological processes, significant efforts have been made in the discovery of CypA inhibitors in the past decade [12][13][14][15][16][17].…”