Diamine derivatives containing imidazolidinylidene propanedinitrile as a new class of histamine H3 receptor antagonists. Part I

Ring Enlargement of Three‐Membered Heterocycles by Treatment with In Situ Formed Tricyanomethane

Although the chemistry of elusive tricyanomethane (cyanoform) has been studied during a period of more than 150 years, this compound has very rarely been utilized in the synthesis or modification of heterocycles. Three‐membered heterocycles, such as epoxides, thiirane, aziridines, or 2H‐azirines, are now treated with tricyanomethane, which is generated in situ by heating azidomethylidene‐malonodinitrile in tetrahydrofuran at 45 °C or by adding sulfuric acid to potassium tricyanomethanide. This leads to ring expansion with formation of 2‐(dicyanomethylidene)oxazolidine derivatives or creation of the corresponding thiazolidine, imidazolidine, or imidazoline compounds and opens up a new access to these push–pull‐substituted olefinic products. The regio‐ and stereochemistry of the ring‐enlargement processes are discussed, and the proposed reaction mechanisms were confirmed by using ¹⁵N‐labeled substrates. It turns out that different mechanisms are operating; however, tricyanomethanide is always acting as a nitrogen‐centered nucleophile, which is quite unusual if compared to other reactions of this species.

Kojic acid derivatives as histamine H(3) receptor ligands

The histamine H(3) receptor (H(3)R) is a promising target in the development of new compounds for the treatment of mainly centrally occurring diseases. However, emerging novel therapeutic concepts have been introduced and some indications in the H(3)R field, e.g. migraine, pain or allergic rhinitis, might take advantage of peripherally acting ligands. In this work, kojic acid-derived structural elements were inserted into a well established H(3)R antagonist/inverse agonist scaffold to investigate the bioisosteric potential of γ-pyranones with respect to the different moieties of the H(3)R pharmacophore. The most affine compounds showed receptor binding in the low nanomolar concentration range. Evaluation and comparison of kojic acid-containing ligands and their corresponding phenyl analogues (3-7) revealed that the newly integrated scaffold greatly influences chemical properties (S Log P, topological polar surface area (tPSA)) and hence, potentially modifies the pharmacokinetic profile of the different derivatives. Benzyl-1-(4-(3-(piperidin-1-yl)propoxy)phenyl)methanamine ligands 3 and 4 belong to the centrally acting diamine-based class of H(3)R antagonist/inverse agonist, whereas kojic acid analogues 6 and 7 might act peripherally. The latter compounds state promising lead structures in the development of H(3)R ligands with a modified profile of action.