Recent Advances in the Synthesis of Peptidomimetics via Ugi Reactions

Peptidomimetics have been extensively explored in many area due to their ability to improve pharmacological qualities and interesting biological activities. Cycles could be incorporated in peptides to reduce their flexibility, often enhancing the affinity for a certain receptor. Many efforts have been made to synthesize various peptidomimetics. Among them, the Ugi reaction is a popular way for the synthesis of peptidomimetics because it provides peptide-like products. The Ugi reaction consists of the condensation of an aldehyde or ketone, a carboxylic acid, an amine, and an isocyanide usually giving a linear peptidomimetic. In order to obtain other linear, cyclic or polycyclic peptidomimetics, the acyclic products have to undergo additional transformations or cyclizations. This review covers the years from 2018-2023, regarding the synthesis of linear, cyclic and polycyclic peptidomimetics, employing Ugi reactions eventually followed by post-Ugi transformations. Organo-catalyzed reactions, base-promoted reactions, and metal-free reactions toward peptidomimetics are highlighted.

Synthesis of Luminescent Indolo[2,1-b]quinazolin-6(12H)-ones via a Sequential Ugi/Iodine-Promoted Cyclization/Staudinger/Aza-Wittig Reaction

A new efficient synthesis of indolo[2,1-b]quinazolin-6(12H)-ones via a sequential Ugi/iodine-promoted cyclization/Staudinger/aza-Wittig reaction was developed. The acid catalyzed three-component reactions of 2-azidobenzaldehydes, 2-[2-(trimethylsilyl)ethynyl]benzenamines (or o-aminoacetophenones), and isocyanides gave Ugi-3CR intermediates, which reacted subsequently with I2/DMSO and triphenylphosphine to produce indolo[2,1-b]quinazolin-6(12H)-ones in good overall yields. The obtained indolo[2,1-b]quinazolin-6(12H)-ones were all colored in bright red or orange. Their luminescent property was studied preliminarily and some of them showed high molar absorption coefficients, strong fluorescence emission intensity, and good absolute light quantum yields.

Post-Ugi Cyclizations Towards Polycyclic N-Heterocycles

The Ugi reaction has become one of the highly explored reactions for the formation of multifunctional adducts, due to the mild reaction conditions, wide scope and high variability. By carefully selecting the starting four components, Ugi-adducts could undergo different kinds of post-transformations for the synthesis of bioactive heterocycles, natural products and macrocycles. Considering the significance of polycycles, diverse post-Ugi transformations have been developed over the years for constructing structurally novel polycycles. In this account, we summarize important efforts for the synthesis of polycyclic N-heterocycles via post-Ugi cyclizations from the Van der Eycken laboratory onwards 2016. With the aid of transition metal catalysis from gold, rhodium, silver and palladium, as well as metal-free strategies, versatile polyheterocycles are prepared with high efficiency and step-economy.

Stereoselective Synthesis of 12-Tetrazolyl Substituted (E)-5H-Quinazolino[3,2-a]quinazolines via Sequential Ugi-Azide/Staudinger/aza-Wittig/Addition/Ag(I)-Catalyzed Cyclization

A new efficient and stereoselective synthesis of 12-tetrazolyl substituted (E)-5H-quinazolino[3,2-a]quinazolines via sequential Ugi-azide/Staudinger/aza-Wittig/addition/Ag(I)-catalyzed cyclization was developed. The four-component reactions of 2-azidobenzaldehyde, 2-(alkynyl)benzenamine, isocyanide, and trimethylsilyl azide gave Ugi-azide intermediates, which were subsequently treated with triphenylphosphine and isocyanate to produce 12-tetrazolyl substituted (E)-5H-quinazolino[3,2-a]quinazolines in the presence of Ag(I) catalyst and K₂CO₃.