(1R,12S,13R,14S,17S,18E,21R,24R,25S,27R)-12-[(E)-1-[(1R,3R,4S)-4-chloro-3-methoxycyclohexyl]prop-1-en-2-yl]-17-ethyl-1,14-dihydroxy-23,25-dimethoxy-13,19,21,27-tetramethyl-11,28-dioxa-4-azatricyclo[22.3.1.04,9]octacos-18-ene-2,3,10,16-tetrone
Pimecrolimus is a 33-epi-chloro-derivative of the ascomycin macrolactam with immunosuppressant property. Pimecrolimus binds to the receptor macrophilin-12 (FKBP-12) forming a complex that blocks the calcium-dependent signal transduction cascade mediated by calcineurin. Via dephosphorylation, calcineurin is the enzyme responsible for activating nuclear factor of activated T-cells (NF-AT), a T cell transcriptional regulatory factor. As a consequence, the synthesis and release of Th1- (T helper 1) and Th2- (T helper 2) type cytokines, and other inflammatory mediators from T-cells and mast cells are blocked and the expression of signals essential for the activation of inflammatory T-lymphocytes is inhibited. However, pimecrolimus mode of action is cell-selective and does not affect Langerhans' cells/dendritic cells and primary fibroblasts.