Ugi four-multicomponent reaction based synthesis, in vitro, and in silico enzymatic evaluations of new pyrazino[1,2-a]indole-1,4-dione-indole-2-phenylacetamides as potent inhibitors against α-glucosidase and α-amylase

In this work, synthesis and evaluation of pyrazino[1,2-a]indole-1,4-dione-indole-2-phenylacetamides 6 a-k as new synthetic anti-diabetes agents were presented. These compounds were synthesized by a four-component Ugi reaction without metal catalyst. All synthesized compounds were evaluated against α-glucosidase and α-amylase as two important targets in the treatment of diabetes. Approximately, all new compounds 6 a-k were more potent than positive control acarbose against these studied enzymes. The obtained potent compounds against the target enzymes were docked in the active site of the related enzyme. Docking study showed that our new potent compounds as well interacted with key residues of the target enzyme.

Enantioselective Access to Chiral 2,5-Diketopiperazines via Stereogenic-at-Cobalt(III)-Catalyzed Ugi-4CRs/Cyclization Sequences

An asymmetric synthesis of chiral 2,5-diketopiperazines by the Ugi-4CR/cyclization is exhibited. The employment of catalytic anionic chiral Co(III) complexes delivered α-propiolyl aminoamides in high yields with excellent enantioselectivities (31 examples, up to 95% ee). The following treatment of Ugi-adducts with PPh3 leads to chiral 2,5-DKPs without significant loss of enantioselectivities (26 examples, up to 91% ee).

Concise Synthesis of 2,5-Diketopiperazines via Catalytic Hydroxy-Directed Peptide Bond Formations

2,5-Diketopiperazines (DKPs) with hydroxymethyl functional groups are essential structures found in many bioactive molecules and functional materials. We have established a simple protocol for the concise synthesis of this type of DKPs through diboronic acid anhydride-catalyzed hydroxy-directed peptide bond formations. The sequential reactions in this report, which consist of three steps, an intermolecular catalytic condensation reaction in which water is the only byproduct, a simple deprotection of the nitrogen-protecting group, and an intramolecular cyclization, enabled the synthesis of functionalized DKPs in high to excellent yields without any intermediate purification. The utility of this protocol has been demonstrated by synthesizing natural products, phomamide and Cyclo(Deala-l-Leu).

A C-H Activation Approach to the Tricyclic Core of Glionitrin A and B

Synthesis of diketopiperazines has been of long-standing interest in both natural product synthesis and medicinal chemistry. Here, we present an operationally convenient and efficient approach to the fused indoline-diketopiperazine tricyclic core of glionitrin A/B and related structures using a Pd-catalyzed C-H activation reaction to form the indoline five-membered ring. Exploratory work aimed at elaborating the tricyclic structures into the corresponding natural products is discussed.

Camphorsulfonic Acid-Mediated One-Pot Tandem Consecutive via the Ugi Four-Component Reaction for the Synthesis of Functionalized Indole and 2-Quinolone Derivatives by Switching Solvents

A camphorsulfonic acid-mediated one-pot tandem consecutive approach was developed to synthesize functionalized indole and 2-quinolone derivatives from the Ugi four-component reaction by switching solvents. A reaction of the Ugi adduct in an aprotic solvent undergoes 5-exo-trig cyclization to form an indole ring. In a protic solvent, however, the Ugi adduct undergoes an alkyne-carbonyl metathesis reaction to form a 2-quinolone ring.