Synthetic Chemistry with N-Acyliminium Ions derived from Piperazine-2,5-diones and Related Compounds

The ubiquity of the piperazine-2,5-dione core (2,5-diketopiperazine, DKP) in natural products and the preponderance of this heterocyclic framework in many bioactive compounds have encouraged the development of methods for the selective functionalization of readily available piperazine-2,5-dione substrates. C-functionalization using DKPs as electrophilic glycine templates is generally mediated by N-acyliminium ions. These intermediates show highly versatile reactivities, which are reflected in an impressive number of synthetic applications. However, even in some highly comprehensive treatments of Nacyliminium ions, references to the construction of these species on piperazine-2,5-dione frameworks are scarce. The present review aims at filling this gap, placing emphasis upon the construction of endocyclic and exocyclic acyliminium ions derived from piperazine-2,5- diones and their synthetic applications. More complex structures that include this framework as a structural fragment, such as pyrazino[1,2-b]isoquinoline-1,4-diones or pyrazino[2,1- b]quinazoline-3,6-diones, are also overviewed.

Keywords: Piperazine-2, 5-dione, 2, 5-diketopiperazine, DKP, N-acyliminium ions, privileged structures, dipeptide dimer, electrophilic glycine templates, protein β-turn mimics, natural products, pyrazino[2, 1-b]quinazoline-3, 6-diones, 1, 5-imino-3-benzazocins, N-acetylardeemin, bicyclomycin, dragmacidin B, phthalascidin analogs, antitumor tetrahydroisoquinoline alkaloids, trabectedin, saframycins A and B, quinocarcin, meta- and para-2, 6- diazacyclophanes, fumiquinazoline C, alantrypinone.