Stapled peptides derived from the Ugi macrocyclization comprise a special class of cyclopeptides with an N-substituted lactam bridge cross-linking two amino acid side chains. Herein we report a comprehensive analysis of the structural factors influencing the secondary structure of these cyclic peptides in solution. Novel insights into the s-cis/s-trans isomerism and the effect of N-functionalization on the conformation are revealed.

A solid-phase approach including on-resin Ugi reactions was developed for the construction of β-hairpins. Various N-alkylated dipeptide fragments proved capable of aligning antiparallel β-sheets in a macrocyclic scaffold, thus serving as β-hairpin templates. Gramicidin S was used as the model β-hairpin to compare the Ugi-derived β-turns with the type-II′ β-turn. The results show that the multicomponent incorporation of such N-alkylated residues allows for the simultaneous stabilization and exo-cyclic functionalization of cyclic β-hairpins.

The enormous diversity of terpenes found in nature is generated by enzymes known as terpene synthases, or cyclases. Some are also known for their ability to convert a single substrate into multiple products. This review comprises monoterpene and sesquiterpene synthases that are multiproduct in nature along with the regulation factors that can alter the product specificity of multiproduct terpene synthases without genetic mutations. Variations in specific assay conditions with focus on shifts in product specificity based on change in metal cofactors, assay pH and substrate geometry are described. Alterations in these simple cellular conditions provide the organism with enhanced chemodiversity without investing into new enzymatic architecture. This versatility to modulate product diversity grants organisms, especially immobile ones like plants with access to an enhanced defensive repertoire by simply altering cofactors, pH level and substrate geometry.

A multicomponent approach enabling the installation of turn-inducing moieties that facilitate the macrocyclization of short and medium-size oligopeptides is described. The strategy comprises the Ugi ligation of peptide carboxylic acids and isocyanopeptides in the presence of aldehydes and acid or photolabile amines followed by cyclization and cleavage of the backbone N-substituents to render canonical cyclopeptides. Implementing the approach on solid phase with the use of Rink amide resins led to a new class of backbone amide linker strategy.

A multicomponent macrocyclization strategy towards cyclic lipopeptides is described. The approach relies on the utilization of the Ugi and Passerini multicomponent reactions for the cyclization of peptides and oxo-peptides, and here it is employed for the construction of a small library of analogues of the natural products mycosubtilin and surfactin A. A key feature of this method is the simultaneous incorporation of either one or two exocyclic lipid tails along with the macrocyclic ring closure, which is only possible due to the multicomponent nature of the macrocyclization step. The evaluation of the anticancer activity of the lipopeptide library showed that the installation of a second lipid moiety in the surfactin scaffold leads to a more potent cytotoxicity in cancer cells. This is a new example of the multicomponent reaction potential in rapidly producing natural product analogues for biological screening.

A new multicomponent methodology for the solution- and solid-phase macrocyclization of peptides is described. The approach comprises the utilization of the Ugi–Smiles reaction for the cyclization of 3-nitrotyrosine-containing peptides either by the N-terminus or the lysine side-chain amino groups. Both the on-resin and solution cyclizations took place with good to excellent efficiency in the presence of an aldehyde and a lipidic isocyanide, while the use of paraformaldehyde required an aminocatalysis-mediated imine formation prior to the on-resin Ugi–Smiles ring closure. The introduction of a turn motif in the peptide sequence facilitated the cyclization step, shortened the reaction time, and delivered crude products with >90% purity. This powerful method provided a variety of structurally novel N-aryl-bridged cyclic lipopeptides occurring as single atropisomers

For the first time, spin-labelled coumpounds have been obtained by isonitrile-based multi component reactions (IMCRs). The typical IMCR Ugi-protocols offer a simple experimental setup allowing structural variety by which labelled diketopiperazines (DKPs) and peptide–peptoid chimera have been synthesized. The reaction keeps the paramagnetic spin label intact and offers a simple and versatile route to a large variety of new and chemically diverse spin labels.

Increasing the diversity of peptide cyclization methods is an effective way of accessing new types of macrocyclic chemotypes featuring a wide variety of ring sizes and topologies. Multicomponent reactions (MCRs) are processes capable of generating great levels of molecular diversity and complexity at low synthetic cost. In an attempt to further exploit MCRs in the field of cyclopeptides, we describe a bidirectional multicomponent approach for the synthesis of N-alkylated macrocyclic peptides of varied sequences and cross-linking positions. The process relies on the execution of two Ugi reactions between peptide diacids and diisocyanides. Varying the amino component enabled the installation of exocyclic elements of diversity, while skeletal diversity was created through different side chain and backbone cyclizations. This procedure shows prospects for the rapid scanning of the chemical space of macrocyclic peptides for applications in chemical biology and drug discovery.

The multiproduct sesquiterpene synthase MtTPS5 from Medicago truncatula catalyzes the conversion of farnesyl diphosphate (FDP) into a complex mixture of 27 terpenoids. 3-Bromo substrate analogues of geranyl diphosphate (3-BrGDP) and farnesyl diphosphate (3-BrFDP) were evaluated as substrates of MTPS5 enzyme. Kinetic studies demonstrated that these compounds were highly potent competitive inhibitors of the MtTPS5 enzyme with fast binding and slow reversibility. Since there is a lack of knowledge about the crystal structure of multiproduct terpene synthases, these molecules might be ideal candidates for obtaining a co-crystal structure with multiproduct terpene synthases. Due to the structural and mechanistic similarity between various terpene synthases we expect these 3-bromo isoprenoids to be ideal probes for crystal structure studies.

There is a wide range of immobilisation reactions to tether substrates to a variety of surfaces for array-based analysis. Most of these immobilisation strategies are specific for a particular surface and require an additional linker to be attached to the substrate or the surface. Furthermore, the analysis of functionalised surfaces is often restricted to certain analytical techniques and therefore, different immobilisation strategies for different surfaces are desirable. Here we have tested an S-tritylated linker for non-covalent or covalent immobilisation of mannosides to polystyrene or gold surfaces. S-Tritylated mannosides with varying linkers were readily synthesised and used to add to biorepulsive maleimide-terminated preformed SAMs after in situ deprotection of the S-trityl group. In addition, S-tritylated mannosides themselves formed stable glycoarrays on polystyrene microtiter plates. The glycoarrays were successfully analysed by MALDI-ToF mass spectrometry, SPR spectroscopy, and interrogated with GFP-transfected Escherichia coli cells. This work has shown that a dual purpose linker can be used on multiple surfaces to form arrays allowing for different testing as well as analytical approaches.