Total Synthesis of (+)-Madindoline A and (−)-Madindoline B, Potent, Selective Inhibitors of Interleukin 6. Determination of the Relative and Absolute Configurations

Biological activity of a novel nonpeptide antagonist to the interleukin-6 receptor 20S,21-epoxy-resibufogenin-3-formate

Interleukin (IL)-6 is a key mediator in the regulation and coordination of the immune response and participates in pathogenesis of cancer cachexia, autoimmune disease, and postmenopausal osteoporosis. In the course of a screening program aimed at IL-6 inhibitor from natural products, we isolated 20S,21-epoxy-resibufogenin-3-formate (ERBF) from bufadienolide and examined the effect of ERBF on activities of various cytokines. ERBF dose dependently suppressed IL-6 activity and caused a parallel rightward shift of dose-response curves to IL-6 at concentrations of 0.03 to 10 ng/ml. Analysis of data yields a pA(2) of 5.12 and a slope of 0.99. Selectivity of ERBF on activity of cytokines was examined using cytokine-dependent cell lines. ERBF did not affect IL-2-dependent growth of CTLL-2 cells, IL-3-dependent growth of Baf3 cells, or tumor necrosis factor (TNF)alpha-induced growth suppression in TNFalpha-sensitive L929 cells. ERBF also did not affect IL-4-stimulated expression of FcepsilonR II receptor (CD23) in U-937 cells, the IL-8-induced chemotaxis of human neutrophils, or nerve growth factor-stimulated neuronal differentiation in PC-12 cells. In contrast, ERBF dose dependently suppressed IL-6-induced neuronal differentiation in PC-12 cells. Furthermore, ERBF suppressed only IL-6-induced osteoclast formation without affecting osteoclast formation induced by IL-11, leukemia inhibitory factor, and 1alpha,25-dihydroxyvitamin D(3). In receptor binding assay, unbound (free) IL-6 was increased in a dose-dependent manner by pretreatment with ERBF on IL-6 receptor (IL-6R), suggesting that ERBF suppresses binding of IL-6 to IL-6R. These results clearly indicate that ERBF is a novel specific small molecule to show IL-6 receptor antagonist activity.

Synthesis of (+/-)-madindolines and chemical models. Studies of chemical reactivity

[reaction: see text] The madindolines are believed to inhibit cytokine signaling through the gp130 receptor. Model compounds of madindolines were synthesized and tested for thiol reactivity. The heterocyclic moiety of madindoline was shown to form thiol adducts via the Savige-Fontana reaction. The enedione moiety was found to be unreactive toward simple thiols unless the quaternary center was removed. Using the powerful Moore reaction, we have synthesized (+/-)-madindoline A and B in 11 steps.

Short total synthesis of (+)-madindolines A and B

[reaction: see text] A short and efficient total synthesis of (+)-madindolines A (1) and B (2), potent and selective inhibitors of interleukin 6, has been achieved. The synthesis features a key chelation-controlled 1,4-diastereoselective acylation to generate the quaternary carbon and an intramolecular acylation of allylsilane to build up the cyclopentene unit.

Synthesis of 2,3-disubstituted pyrrolidines and piperidines via one-pot oxidative decarboxylation-beta-iodination of amino acids

A new synthesis of 2,3-disubstituted pyrrolidines and piperidines is described. This mild procedure is based on the one-pot oxidative decarboxylation-beta-iodination of alpha-amino acid carbamates or amides. The iodine is introduced at the previously unfunctionalized 3-position. Different substituents can be introduced at C-2, e.g., hydroxy, alkoxy, allyl, alkyl, etc. A trans relationship between the C-2 and C-3 substituents is exclusively obtained. The influence of the solvent and the ring size of the starting amino acid are studied, as well as the nature of the protecting group on the nitrogen. The stereoselectivity of the reaction was also studied using chiral methyl (2S,4S)-4-acetyloxyproline-1-carboxylate (8). The products obtained can be manipulated to give bicyclic systems present in many natural products. By using the tandem decarboxylation-iodination-alkylation reaction, 2-substituted-3-iodopyrrolidines are formed, which are precursors of 2-substituted-2,5-dihydropyrrols.