A series of structurally amphiphilic biscationic norbornanes have been synthesised as rigidified, low molecular weight peptidomimetics of cationic antimicrobial peptides. A variety of charged hydrophilic functionalities were attached to the norbornane scaffold including aminium, guanidinium, imidazolium and pyridinium moieties. Additionally, a range of hydrophobic groups of differing sizes were incorporated through an acetal linkage. The compounds were evaluated for antibacterial activity against both Gram-negative and Gram-positive bacteria. Activity was observed across the series; the most potent of which exhibited an MIC's ≤ 1 μg mL(-1) against Streptococcus pneumoniae, Enterococcus faecalis and several strains of Staphylococcus aureus, including multi-resistant methicillin resistant (mMRSA), glycopeptide-intermediate (GISA) and vancomycin-intermediate (VISA) S. aureus.

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This short report describes an improved, reliable, and high-yielding (>90%) synthesis of 2-[2,3-bis(tert-butoxycarbonyl)guanidino]ethylamine. The method is scalable (>5 g), and the product obtained directly from the reaction mixture requires no further purification. In addition, this methodology can be successfully applied to other diamine substrates (1,3-propyl and 1,4-butyl; 70% and 61% yield, respectively).