Piperazines monocyclic

Compared with monocyclic piperazine scaffolds, bicyclic piperazines often provide platforms with even more points of diversity compared to monocyclic piperazines. Condensed bicyclic piperazines enlarge the chemical space of piperazine scaffolds, as well as the family of target proteins. For example, bicyclic piperazinones were prepared and evaluated in vitro and in vivo as thrombin inhibitors [49]. The cocrystal structure of a bicyclic piperazinone inhibitor 154 with thrombin was shown in Fig. 9. So far, chemists have developed many MCR methods to synthesize a variety of bicyclic piperazine scaffolds. 

Some interesting results were obtained by comparative investigation of the infrared (IR) spectra of quinuclidine, -substituted piperidines, and piperazines.27 Monocyclic compounds gave at 2700-2800 cm-1 characteristic absorption bonds attributable to interaction between the nitrogen lone-pair electrons and the neighboring axial CH bonds. Quinuclidine does not absorb in this region, probably because of the absenceof such interaction in the quinuclidine ring. There are absorption bands characteristic of quinuclidine at 2430, 2915, and 3405 cm"1.28... 

Catalytic hydrogenation of perhydropyrazino[2,3-ft]pyrazines provides monocyclic piperazines. In other ways the compound behaves as a tetramine, forming a tetrahydrochloride and reacting with four moles of acetic anhydride, phenyl isocyanate, and phenyl isothiocyanate. ... 

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