One-Step Synthesis of 2,5-Diaminoimidazoles and Total Synthesis of Methylglyoxal-Derived Imidazolium Crosslink (MODIC)

Pentosinane, a Post-Translational Modification of Human Proteins with Underappreciated Stability

Pentosinane is a structurally complex nonenzymatic post-translational modification of proteins believed to be present in all living things. It falls into the category of advanced glycation end products (AGEs) and is structurally related to the other AGEs pentosidine and glucosepane. Although pentosidine and glucosepane have been widely studied for their role in wide-ranging conditions (e.g., diabetes mellitus, Alzheimer's disease, and human aging), relatively little is known about pentosinane. Interestingly, previous reports have suggested that pentosidine may derive from pentosinane. The (patho)physiological significance of pentosinane in humans is largely unexplored. As a first step to address this knowledge gap, we report herein the first total synthesis of pentosinane. Our synthesis is high yielding (1.7% over seven steps), concise, and enantioselective, and it leverages a strategy for synthesizing 2,5-diaminoimidazoles previously developed by our lab. Access to synthetic pentosinane has allowed us to perform additional studies showing that its oxidation to pentosidine is both pH and oxygen dependent and is substantially slower under physiological conditions than previously believed. Additionally, pentosinane rapidly decomposes under harshly acidic conditions typically employed for pentosidine isolation. Taken together, these results suggest that pentosinane is likely to be more abundant in vivo than previously appreciated. We believe these results represent a critical step toward illuminating the role(s) of pentosinane in human biology.

Oxoammonium Salt-Promoted Multifunctionalization of Saturated Cyclic Amines Based On β-Oxo Cyclic Iminium Ion Intermediates

Herein we describe a convenient method for multiple C(sp³)-H bond functionalization of saturated cyclic amines through oxoammonium salt-promoted oxidation to afford a β-oxo cyclic iminium ion as a key intermediate, followed by cascade addition with thiocyanate and diverse N-, O-, and S-containing nucleophiles in the green solvent and EtOH. Notably, chiral spiro azapolyheterocycles were prepared enantioselectively (>20:1 dr, up to 99% ee) when cysteine or serine esters were used as substrates. Moreover, the concise late-stage modification of several natural product derivatives was accomplished using this method.

One-Step Synthesis of 2,5-Diaminoimidazoles and Total Synthesis of Methylglyoxal-Derived Imidazolium Crosslink (MODIC)

Here we describe a general method for the synthesis of 2,5-diaminoimidazoles, which involves a thermal reaction between α-aminoketones and substituted guanylhydrazines without the need for additives. As one of the few known ways to access the 2,5-diaminoimidazole motif, our method greatly expands the number of reported diaminoimidazoles and further supports our previous observations that these compounds spontaneously adopt the non-aromatic 4(H) tautomer. The reaction works successfully on both cyclic and acyclic amino ketone starting materials, as well as a range of substituted guanylhydrazines. Following optimization, the method was applied to the efficient synthesis of the advanced glycation end product (AGE) methylglyoxal-derived imidazolium crosslink (MODIC). We expect that this method will enable rapid access to a variety of biologically important 2,5-diaminoimidazole-containing products.