Synthesis of natural product hybrids by the Ugi reaction in complex media containing plant extracts

Ammonium carboxylates in the ammonia-Ugi reaction: one-pot synthesis of α,α-disubstituted amino acid derivatives including unnatural dipeptides

Despite the remarkable developments of the Ugi reaction and its variants, the use of ammonia in the Ugi reaction has long been recognized as impractical and unsuccessful. Indeed, the ammonia-Ugi reaction often requires harsh reaction conditions, such as heating and microwave irradiation, and competes with the Passerini reaction, thereby resulting in low yields. This study describes a robust and practical ammonia-Ugi reaction protocol. Using originally prepared ammonium carboxylates in trifluoroethanol, the ammonia-Ugi reaction proceeded at room temperature in high yields and showed a broad substrate scope, thus synthesizing a variety of α,α-disubstituted amino acid derivatives, including unnatural dipeptides. The reaction required no condensing agents and proceeded without racemization of the chiral stereocenter of α-amino acids. Furthermore, using this protocol, we quickly synthesized a novel dipeptide, D-Leu-Aic-NH-CH2Ph(p-F), which exhibited a potent inhibitory activity against α-chymotrypsin with a Ki value of 0.091 μM.

Derivatization of Abietane Acids by Peptide-like Substituents Leads to Submicromolar Cytotoxicity at NCI-60 Panel

Natural compounds, including diterpenoids, play a critical role in various biological processes and are recognized as valuable components in cancer treatment. Isocyanides multicomponent reactions (IsMCRs) are one of the effective methods to obtain adducts at the carboxyl group with a peptide-like substituent. In this study, dehydroabietic acid and levopimaric acid diene adducts as the starting scaffolds were modified by the multicomponent Passerini (P-3CR) and Ugi (U-4CR) reactions to afford α-acyloxycarboxamides and α-acylaminocarboxamides. A group of twenty novel diterpene hybrids was subjected to NCI in vitro assessment, and a consistent structure-activity relationship was established. Eleven of the synthesized derivatives inhibited the growth of cancer cells of 4 to 39 cell lines in one dose assay, and the most active were derivatives 3d, 9d, and 10d holding a fragment of 1a,4a-dehydroquinopimaric acid. They were selected for a five-dose analysis and demonstrated a significant antiproliferative effect towards human cancer cell lines. The outstanding cytotoxic activity was observed for the P-3CR product 3d with growth inhibitory at submicromolar and micromolar concentrations (GI50 = 0.42-3 μM) against the most sensitive cell lines. The U-4CR products 9d and 10d showed selective activity against all leukemia cell lines with GI50 in the range of 1-17 µM and selectivity indexes of 5.49 and 4.72, respectively. Matrix COMPARE analysis using the GI50 vector showed a moderate positive correlation of compound 3d with standard anticancer agents that can influence kinase receptors and epidermal growth factor receptors (EGFRs). The ADMET analysis acknowledges the favorable prognosis using compounds as potential anticancer agents. The obtained results indicate that these new hybrids could be useful for the further development of anticancer drugs, and 1a,4a-dehydroquinopimaric acid derivatives could be recommended for in-depth studies and the synthesis of new antitumor analogs on their basis.

Chemically engineered essential oils prepared through thiocyanation under solvent-free conditions: chemical and bioactivity alteration

The generation of chemically engineered essential oils (CEEOs) prepared from bi-heteroatomic reactions using ammonium thiocyanate as a source of bioactive compounds is described. The impact of the reaction on the chemical composition of the mixtures was qualitatively demonstrated through GC-MS, utilizing univariate and multivariate analysis. The reaction transformed most of the components in the natural mixtures, thereby expanding the chemical diversity of the mixtures. Changes in inhibition properties between natural and CEEOs were demonstrated through acetylcholinesterase TLC autography, resulting in a threefold increase in the number of positive events due to the modification process. The chemically engineered Origanum vulgare L. essential oil was subjected to bioguided fractionation, leading to the discovery of four new active compounds with similar or higher potency than eserine against the enzyme. The results suggest that the directed chemical transformation of essential oils can be a valuable strategy for discovering new acetylcholinesterase (AChE) inhibitors.

Expanding Chemical Frontiers: Approaches for Generating Diverse and Bioactive Natural Product-Like Compounds Libraries from Extracts

The realms of natural products and synthetic compounds exhibit distinct chemical spaces that not only differ but also complement each other. While the convergence of these two domains has been explored through semisynthesis and conventional pharmacomodulation endeavours applied to natural frameworks, a recent and innovative approach has emerged that involves the combinatorial generation of libraries of 'natural product-like compounds' (NPLCs) through the direct synthetic derivatization of natural extracts. This has led to the production of numerous NPLCs that incorporate structural elements from both their natural (multiple saturated rings, oxygen content, chiral centres) and synthetic (aromatic rings, nitrogen and halogen content, drug-like properties) precursors. Through careful selection of extracts and reagents, specific bioactivities have been achieved, and this strategy has been deployed in various ways, showing great promise without reaching its full potential to date. This review seeks to provide an overview of reported examples involving the chemical engineering of extracts, showcasing a spectrum of natural product alterations spanning from simple substitutions to complete scaffold remodelling. It also includes an analysis of the accomplishments, perspectives and technical challenges within this field.

Relevant Developments in the Use of Three-Component Reactions for the Total Synthesis of Natural Products. The last 15 Years

Multicomponent reactions (MCRs) offer a highly useful and valuable strategy that can fulfill an important role in synthesizing complex polysubstituted compounds, by simplifying otherwise long sequences and increasing their efficiency. The total synthesis of selected natural products employing three-component reactions as their common strategic MCR approach, is reviewed on a case-by-case basis with selected targets conquered during the last 15 years. The revision includes detailed descriptions of the selected successful sequences; relevant information on the isolation, and bioactivity of the different natural targets is also briefly provided.

Recent developments in the total synthesis of natural products using the Ugi multicomponent reactions as the key strategy

The total syntheses of selected natural products using different versions of the Ugi multicomponent reaction is reviewed on a case-by-case basis. The revision covers the period 2008-2023 and includes detailed descriptions of the synthetic sequences, the use of state-of-the-art chemical reagents and strategies, as well as the advantages and limitations of the transformation and some remedial solutions. Relevant data on the isolation and bioactivity of the different natural targets are also briefly provided. The examples clearly evidence the strategic importance of this transformation and its key role in the modern natural products synthetic chemistry toolbox. This methodology proved to be a valuable means for easily building molecular complexity and efficiently delivering step-economic syntheses even of intricate structures, with a promising future.

Molecular Hybridization of Alkaloids Using 1,2,3-Triazole-Based Click Chemistry

Alkaloids found in multiple species, known as 'driver species', are more likely to be included in early-stage drug development due to their high biodiversity compared to rare alkaloids. Many synthetic approaches have been employed to hybridize the natural alkaloids in drug development. Click chemistry is a highly efficient and versatile reaction targeting specific areas, making it a valuable tool for creating complex natural products and diverse molecular structures. It has been used to create hybrid alkaloids that address their limitations and serve as potential drugs that mimic natural products. In this review, we highlight the recent advancements made in modifying alkaloids using click chemistry and their potential medicinal applications. We discuss the significance, current trends, and prospects of click chemistry in natural product-based medicine. Furthermore, we have employed computational methods to evaluate the ADMET properties and drug-like qualities of hybrid molecules.

Ugi Four-Component Reactions Using Alternative Reactants

The Ugi four-component reaction (Ugi-4CR) undoubtedly is the most prominent multicomponent reaction (MCRs) that has sparked organic chemists' interest in the field. It has been widely used in the synthesis of diverse heterocycle molecules such as potential drugs, natural product analogs, pseudo peptides, macrocycles, and functional materials. The Ugi-4CRs involve the use of an amine, an aldehyde or ketone, an isocyanide, and a carboxylic acid to produce an α-acetamido carboxamide derivative, which has significantly advanced the field of isocyanide-based MCRs. The so-called intermediate nitrilium ion could be trapped by a nucleophile such as azide, N-hydroxyphthalimide, thiol, saccharin, phenol, water, and hydrogen sulfide instead of the original carboxylic acid to allow for a wide variety of Ugi-type reactions to occur.β In addition to isocyanide, there are alternative reagents for the other three components: amine, isocyanide, and aldehyde or ketone. All these alternative components render the Ugi reaction an aptly diversity-oriented synthesis of a myriad of biologically active molecules and complex scaffolds. Consequently, this review will delve deeper into alternative components used in the Ugi MCRs, particularly over the past ten years.

Ugi Adducts as Novel Anti-austerity Agents against PANC-1 Human Pancreatic Cancer Cell Line: A Rapid Synthetic Approach

Pancreatic cancer cells have an inherent tolerance to withstand nutrition starvation, allowing them to survive in hypovascular tumor microenvironments that lack of sufficient nutrients and oxygen. Developing anti-cancer agents that target this tolerance to nutritional starvation is a promising anti-austerity strategy for eradicating pancreatic cancer cells in their microenvironment. In this study, we employed a chemical biology approach using the Ugi reaction to rapidly synthesize new anti-austerity agents and evaluate their structure-activity relationships. Out of seventeen Ugi adducts tested, Ugi adduct 11 exhibited the strongest anti-austerity activity, showing preferential cytotoxicity against PANC-1 pancreatic cancer cells with a PC50 value of 0.5 µM. Further biological investigation of Ugi adduct 11 revealed a dramatic alteration of cellular morphology, leading to PANC-1 cell death within 24 h under nutrient-deprived conditions. Furthermore, the R absolute configuration of 11 was found to significantly contribute to the preferential anti-austerity ability toward PANC-1, with a PC50 value of 0.2 µM. Mechanistically, Ugi adduct (R)-11 was found to inhibit the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling pathway preferentially under nutrition starvation conditions. Consequently, Ugi-adduct (R)-11 could be a promising candidate for drug development targeting pancreatic cancer based on the anti-austerity strategy. Our study also demonstrated that the Ugi reaction-based chemical engineering of natural product extracts can be used as a rapid method for discovering novel anti-austerity agents for combating pancreatic cancer.