Several 7-peptide-substituted pterins were synthesized and tested as competitive active-site inhibitors of Ricin Toxin A (RTA). Focus began on dipeptide conjugates, and these results further guided the construction of several tripeptide conjugates. The binding of these compounds to RTA was studied via a luminescence-based kinetic assay, as well as through X-ray crystallography. Despite the relatively polar, solvent exposed active site, several hydrophobic interactions, most commonly π-interactions, not predicted by modeling programs, were identified in all of the best-performing inhibitors. Nearly all of these compounds provide IC50’s in the low μM range.

The optimization of a series of pterin amides for use as Ricin Toxin A (RTA) inhibitors is reported. Based upon crystallographic data of a previous furan-linked pterin, various expanded furans were synthesized, linked to the pterin and tested for inhibition. Concurrently, hetero-analogs of furan were explored, leading to the discovery of more potent triazol-linked pterins. Additionally, we discuss a dramatic improvement in the synthesis of these pterin amides via a dual role by diazabicycloundecene (DBU). This synthetic enhancement facilitates rapid diversification of the previously challenging pterin heterocycle, potentially aiding future medicinal research involving this structure.

Herein, we present the crystal structure, NMR J analysis, and conformational and natural bond order analyses of tricyclic oxocane (1), resulting in the discovery of a long-range Perlin effect at C4 and C5. The normal Perlin effect (NPE) of Δ(1)JC-H = 18.38 Hz at C5 is the largest to date for a nonanomeric methylene due to an unprecedented through-space n → σ* stabilizing interaction. The NPE at C4 where Δ(1)JC-H = 6.91 Hz is nearly double those found in cyclohexanone.

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