Solid-phase synthesis of a pepticinnamin E library

Discovery and optimization of 4-(imidazo[1,2-a]pyrimidin-3-yl)thiazol-2-amine derivatives as novel phosphodiesterase 4 inhibitors

Phosphodiesterases (PDEs) are important intracellular enzymes that hydrolyze the second messengers cAMP and/or cGMP. Now several studies have shown that PDE4 received particular attention due to which it represents the most prominent cAMP-metabolizing enzyme involved in many diseases. In this study, we performed prescreening of our internal compound library and discovered the compound (PTC-209) with moderate PDE4 inhibitory activity (IC50 of 4.78 ± 0.08 μM). And a series of 4-(imidazo[1,2-a]pyrimidin-3-yl)thiazol-2-amine derivatives as novel PDE4 inhibitors starting from PTC-209 were successfully designed and synthesized using a structure-based discovery strategy. L19, the most potent inhibitor, exhibited good inhibitory activity (IC50 of 0.48 ± 0.02 μM) and remarkable metabolic stability in rat liver microsomes. Our study presents an example of discovery novel PDE4 inhibitors, which would be helpful for design and optimization of novel inhibitors in future.

Pepticinnamins N, O, and P, Nonribosomal Peptides from the Soil-Derived Streptomyces mirabilis P8-A2

Cinnamoyl moiety containing nonribosomal peptides represented by pepticinnamin E are a growing family of natural products isolated from different Streptomyces species and possess diverse bioactivities. The soil bacterium Streptomyces mirabilis P8-A2 harbors a cryptic pepticinnamin biosynthetic gene cluster, producing azodyrecins as major products. Inactivation of the azodyrecin biosynthetic gene cluster by CRISPR-BEST base editing led to the activation and production of pepticinnamin E (1) and its analogues, pepticinnamins N, O, and P (2-4), the structures of which were determined by detailed NMR spectroscopy, HRMS data, and Marfey's reactions. These new compounds did not show a growth inhibitory effect against the LNCaP and C4-2B prostate cancer lines, respectively.

An overview on natural farnesyltransferase inhibitors for efficient cancer therapy

As one of the world's five terminally ills, tumours can cause important genetic dysfunction. However, some current medicines for tumours usually have strong toxic side effects and are prone to drug resistance. Studies have found that farnesyltransferase inhibitors (FTIs) extracted from natural materials have a good inhibiting ability on tumours with fewer side effects. This article describes several FTIs extracted from natural materials and clarifies the current research progress, which provides a new choice for the treatment of tumours.

Discovery and Biosynthesis of Pepticinnamins G-M Featuring Three Enzymes-Catalyzed Nonproteinogenic Amino Acid Formation

Since pepticinnamin E was discovered almost 30 years ago, no other pepticinnamin family of natural products has been reported to date. Here, we report the discovery of pepticinnamins G-I (1-3) from a marine Streptomyces sp. PKU-MA01144 and pepticinnamins J-M (4-7) from several mutants, and these new compounds contain different N-methyl-l-alanine and l-tyrosine residues compared to pepticinnamin E. Genome sequencing, heterologous expression, gene deletion, and reconstitution of enzymatic reaction in vitro identified the biosynthetic gene cluster of 1-7 and first experimentally established the biosynthesis of the nonproteinogenic 2-chloro-3-hydroxy-4-methoxy-l-phenylalanine residue by a biopterin-dependent hydroxylase Pep10, an O-methyltransferase Pep9, and a flavin-dependent halogenase Pep1. The biosynthetic research and heterologous expression system in this study set the stage for pathway engineering for more pepticinnamins generation in the future.

Targeted Rediscovery and Biosynthesis of the Farnesyl-Transferase Inhibitor Pepticinnamin E

The natural product pepticinnamin E potently inhibits protein farnesyl transferases and has potential applications in treating cancer and malaria. Pepticinnamin E contains a rare N-terminal cinnamoyl moiety as well as several nonproteinogenic amino acids, including the unusual 2-chloro-3-hydroxy-4-methoxy-N-methyl-L-phenylalanine. The biosynthesis of pepticinnamin E has remained uncharacterized because its original producing strain is no longer available. Here we identified a gene cluster (pcm) for this natural product in a new producer, Actinobacteria bacterium OK006, by means of a targeted rediscovery strategy. We demonstrated that the pcm cluster is responsible for the biosynthesis of pepticinnamin E, a nonribosomal peptide/polyketide hybrid. We also characterized a key O-methyltransferase that modifies 3,4-dihydroxy-l-phenylalanine. Our work has identified the gene cluster for pepticinnamins for the first time and sets the stage for elucidating the unique chemistry required for biosynthesis.

Total Solid-Phase Synthesis of Dehydroxy Fengycin Derivatives

A rapid and efficient solid-phase strategy for the synthesis of dehydroxy fengycins derivatives is described. This synthetic approach involved the linkage of a Tyr to a Wang resin via a Mitsunobu reaction and the elongation of the peptide sequence followed by subsequent acylation of the N-terminus of the resulting linear peptidyl resin, esterification of the phenol group of a Tyr with an Ile, and final macrolactamization. The amino acid composition as well as the presence of the N-terminal acyl group significantly influenced the stability of the macrolactone. Cyclic lipodepsipeptides with a l-Tyr³/d-Tyr⁹ configuration were more stable than those containing the Tyr residues with an opposite configuration. This work constitutes the first approach on the total solid-phase synthesis of dehydroxy fengycin derivatives.

Solid-Phase Synthesis of Cyclic Depsipeptides Containing a Tyrosine Phenyl Ester Bond

The first solid-phase strategy for the synthesis of cyclic depsipeptides containing a phenyl ester linkage in their structure is described. The key steps of the synthesis were the formation of the phenyl ester bond and the on-resin head-to-side-chain cyclization. The amino acid configuration significantly influenced the formation and the stability of the cyclic depsipeptides. The presence of a l-Tyr(1) and a d-Tyr(7) led to the most stable sequences.

Natural Product-Derived Modulators of Cell Cycle Progression and Viral Entry by Enantioselective Oxa Diels-Alder Reactions on the Solid Phase

The underlying frameworks of natural product classes with multiple biological activities can be regarded as biologically selected and prevalidated starting points in vast chemical structure space in the development of compound collections for chemical biology and medicinal chemistry research. For the synthesis of natural product-derived and -inspired compound collections, the development of enantioselective transformations in a format amenable to library synthesis, e.g., on the solid support, is a major and largely unexplored goal. We report on the enantioselective solid-phase synthesis of a natural product-inspired alpha,beta-unsaturated delta-lactone collection and its investigation in cell-based screens monitoring cell cycle progression and viral entry into cells. The screens identified modulators of both biological processes at a high hit rate. The screen for inhibition of viral entry opens up avenues of research for the identification of compounds with antiviral activity.

Identification of mono- and bisubstrate inhibitors of protein farnesyltransferase and inducers of apoptosis from a pepticinnamin E library

A library of 51 analogues of the naturally occurring protein farnesyltransferase inhibitor pepticinnamin E was investigated biologically. Several compounds with pronounced inhibitory activity were discovered with the lowest IC(50) value reaching 1 microM. The library contains inhibitors which are competitive to either farnesylpyrophosphate or the peptide substrate and a bisubstrate inhibitor. This activity is supported and rationalized by molecular modelling experiments and different binding modes of the inhibitors deduced from them. Several compounds induced apoptosis in a Ras-transformed tumour cell line, and in one case this correlated with farnesyltransferase-inhibiting activity.