Unusual Side Chain Research Articles

Cholestan Steroids from The Stem Bark of Aglaia angustifolia Miq and Their Cytotoxic Activity against MCF-7 Breast Cancer Cell Lines

With about 120 species, Aglaia is one of the largest genera of the plant family Meliaceae (the mahogany plants). Various Aglaia species have been investigated since the 1960s for their phytochemical constituents and biological properties. This research objective was to find secondary metabolites that have activity as anti-breast cancer compounds from endemic Indonesian Aglaia, such as Aglaia angustifolia Miq. Two cholestan type steroids, stigmast-5en-3α-acetat (1), as a new steroid with α-sterochemistry of acetyl moiety at C-3 and 23a-homostigmast-5en-3β-ol (2), with unusual side chain were isolated for the first time from the stem bark of Aglaia angustifolia Miq or known as segara tree in Kalimantan. The chemical structures of two steroids were identified with spectroscopic data, including IR, NMR (1H, 13C, DEPT 135°, HMQC, HMBC, NOESY, 1H-1H COSY) and HRTOF-MS, as well as by comparing with previously reported spectral data. These two steroids were isolated for the first time from this genus. Steroids 1 and 2 were evaluated for cytotoxic activity against MCF-7 breast cancer cells and showed weak activity with IC50 values of 829.0 and 903.0 µg/mL, respectively.

Deaminative-cleaved S. monotuberculatus fucosylated glycosaminoglycan: Structural elucidation and anticoagulant activity

Stichopus monotuberculatus is a tropical sea cucumber species and used as a folk medicine and tonic food. In this study, a fucosylated glycosaminoglycan (SmFG), the depolymerized SmFG (dSmFG) and its oligosaccharide fractions were prepared. The SmFG and its depolymerized products were comprised of a chondroitin-sulfate-E backbone, and various sulfated fucose side chains, including an unusual disaccharide side chain connected to the C-3 position of D-glucuronic acid (GlcA) or GlcA-ol. A peeling reaction occurred during the deaminative depolymerization process. The dSmFG and its fractions showed strong anticoagulant activity by selectively inhibiting intrinsic tenase complex, and had no anti-factor IIa, Xa and VIIa activity. The anticoagulant activity reduced with the decrease of molecular weight, and the unusual branch and novel reducing end may enhance the anticoagulant activity. These findings can provide significant information for development and utilization of depolymerized products from SmFG in food and pharmaceutical industries.

Serrulatane diterpenoids with unusual side chain modifications from root bark of Eremophila longifolia

The plant genus Eremophila is endemic to Australia and widespread in arid regions. Root bark extract of Eremophila longifolia (R.Br.) F.Muell. (Scrophulariaceae) was investigated by LC-PDA-HRMS, and dereplication suggested the presence of a series of diterpenoids. Using a combination of preparative- and analytical-scale HPLC separation as well as extensive 1D and 2D NMR analysis, the structures of 12 hitherto unreported serrulatane diterpenoids, eremolongine A-L, were established. These structures included serrulatanes with unusual side chain modifications to form hitherto unseen skeletons with, e.g., cyclopentane, oxepane, and bicyclic hexahydro-1H-cyclopenta[c]furan moieties. Serrulatane diterpenoids in Eremophila have recently been shown to originate from a common biosynthetic precursor with conserved stereochemical configuration, and this was used for tentative assignment of the relative and absolute configuration of the isolated compounds. Triple high-resolution α-glucosidase/α-amylase/PTP1B inhibition profiling demonstrated that several of the eremolongines had weak inhibitory activity towards targets important for management of type 2 diabetes.

Cytotoxic dammarane triterpenoids from the hydrolyzate of Gynostemma pentaphyllum

• Three undescribed triterpenoids with rare skeletons ( 1 - 3 ) were reported. • One unreported gypenoside ( 4 ) was isolated. • The absolute configurations were determined by ECD analysis. • Their antiproliferative effects were evaluated in a variety of cell lines. Three undescribed dammarane-type triterpenoids with rare carbon skeletons ( 1 - 3 ), together with one unreported gypenoside ( 4 ), were isolated from a acid hydrolysis product of Gynostemma pentaphyllum (Thunb.) Makino. Their molecular structures were elucidated via a combination of spectroscopic and spectrometric data, while the absolute configurations of compounds 1 , 2 and 4 were determined by electronic circular dichroism (ECD) analyse. Notably, compounds 1 - 3 possess a 19(10→1)abeo structural moiety in the A ring. Saponin 4 possesses an unusual cyclopentenone side chain. Compounds 1 , 2 and 4 were screened for their antiproliferative effects against HepG2, MCF-7 and DU145 cell lines.

The Discovery of Actinospene, a New Polyene Macrolide with Broad Activity against Plant Fungal Pathogens and Pathogenic Yeasts.

Phytopathogenic fungi infect crops, presenting a worldwide threat to agriculture. Polyene macrolides are one of the most effective antifungal agents applied in human therapy and crop protection. In this study, we found a cryptic polyene biosynthetic gene cluster in Actinokineospora spheciospongiae by genome mining. Then, this gene cluster was activated via varying fermentation conditions, leading to the discovery of new polyene actinospene (1), which was subsequently isolated and its structure determined through spectroscopic techniques including UV, HR-MS, and NMR. The absolute configuration was confirmed by comparing the calculated and experimental electronic circular dichroism (ECD) spectra. Unlike known polyene macrolides, actinospene (1) demonstrated more versatile post-assembling decorations including two epoxide groups and an unusual isobutenyl side chain. In bioassays, actinospene (1) showed a broad spectrum of antifungal activity against several plant fungal pathogens as well as pathogenic yeasts with minimum inhibitory concentrations ranging between 2 and 10 μg/mL.

Withanolide-Type Steroids from Physalis nicandroides Inhibit HIV Transcription.

The aim of the present study is to report the isolation, structural elucidation, and antiviral evaluation of four new withanolide-type steroids, named nicansteroidins A–D (1–4), together with nine related known compounds (5–13) isolated from the aerial parts of Physalis nicandroides. Their structures were established based on an extensive spectroscopic analysis, including 1D and 2D NMR techniques. Outstandingly, nicansteroidins A and B possess an unusual side chain with an exocyclic double bond on the δ-lactone system, whereas nicansteroidins C and D have an uncommon cycloperoxide functionality in ring A as distinct structural motifs. Their biological evaluation as inhibitors of human immunodeficiency virus type 1 replication revealed that two compounds from this series, 7 and 13, displayed strong inhibition of HIV-1 replication with IC50 values lower than 2 μM. Moreover, cellular mechanism experiments showed that the main target of these compounds in the HIV replication cycle is viral transcription. This study is the first report of withanolide-type steroids as HIV inhibitors and provides insight into their potential as candidates for further preclinical studies.

Recent Advance on Chemistry and Bioactivities of Secondary Metabolites from Viburnum Plants: An Update.

Viburnum species are a group of small trees or shrubs that are of great ornamental and medicinal values. Some of them have been used for a long time both as conventional and ethnic medicine. Viburnum fruits, eaten in fresh and processed forms, have been revealed to contain various health-promoting nutrients. With the increasing research on Viburnum plants, they are considered to be an abundant resource of bioactive natural products possessing diverse pharmacological properties and unique chemical structures, that is powerfully proved by the existence of structurally novel vibsane-type diterpenoids which only occur in Viburnum species, newly discovered lignan constituents with unusual side chains and other noteworthy natural components. This review describes 185 new and 228 known secondary metabolites from Viburnum genus between 2008 and 2020, including their chemical structures, sources and bioactivities, and highlights the corresponding structure-activity relationships.

Peptides from diatoms and grasses harness phosphate ion binding to silica to help regulate biomaterial structure

Many life forms generate intricate submicron biosilica structures with various important biological functions. The formation of such structures, from the silicic acid in the waters and in the soil, is thought to be regulated by unique proteins with high repeats of specific amino acids and unusual sidechain modifications.Some silicifying proteins are characterized by high prevalence of basic amino acids in their primary structures. Lysine-rich domains are found, for instance, in diatom silaffin proteins and in the sorghum grass siliplant1 protein. These domains exhibit catalytic activity in silica chain condensation, owing to molecular interactions of the lysine amine groups with the forming mineral. The use of amine chemistry by two very remote organisms has motivated us to seek other molecular biosilicification processes that may be common to the two life forms.In diatom silaffins, domains rich in phosphoserine residues are thought to assist the assembly of silaffin molecules into an organic supra-structure which serves as a template for the silica to precipitate on. This mold, held by salt bridges between serine phosphates and lysine amines, dictates the shape of the silica particles formed. Yet, silica synthesized with the dephosphorylated silaffin in phosphate buffer showed similar morphology to the one prepared with the native protein, suggesting that a defined spatial arrangement of serine phosphates is not required to generate silica with the desired shape. Concurrently, free phosphates enhanced the activity of siliplant1 in silica formation.It is therefore beneficial to characterize the involvement of these anions as co-factors in regulated silicification by functional peptides from the two proteins and to understand whether they play similar molecular role in the mechanism of mineralization.Here we analyze the molecular interactions of free phosphate ions with silica and the silaffin peptide PL12 and separately with silica and siliplant1 peptide SLP1 in the two biomimetic silica products generated by the two peptides. MAS NMR measurements show that the phosphate ions interact with the peptides and at the same time may be forming bonds with the silica mineral. This bridging capability may add another avenue by which the structure of the silica material is influenced. A model for the molecular/ionic interactions at the bio-inorganic interface is described, which may have bearings for the role of phosphorylated residues beyond the function as intermolecular cross linkers or free phosphate ions as co-factors in regulation of silicification. Statement of SignificanceThe manuscript addresses the question how proteins in diatoms and plants regulate the biosilica materials that are produced for various purposes in organisms. It uses preparation of silica in vitro with functional peptide derivatives from a sorghum grass protein and from a diatom silaffin protein separately to show that phosphate ions are important for the control that is achieved by these proteins on the final shape of the silica material produced. It portrays via magnetic resonance spectroscopic measurements, in atomic detail, the interface between atoms in the peptide, atoms on the surface of the silica formed and the phosphate ions that form chemical bonds with atoms on the silica as part of the mechanism of action of these peptides.

Morindolestatin, Naturally Occurring Dehydromorpholinocarbazole Alkaloid from Soil-Derived Bacterium of the Genus Streptomyces.

Novel antilipid peroxidative carbazole alkaloids, antiostatin A5 (1), antiostatin A6 (2), and (±)-morindolestatin (3), were isolated from a new soil-derived Streptomyces sp. Compound 2 possesses an unusual cyclohexene side chain. Compound 3 was a pair of enantiomers featuring an unprecedented [1,4]oxazino[2,3-c]carbazole ring system. The absolute configuration of 3 was determined by online HPLC-ECD and ECD calculation. A racemization mechanism and putative biosynthetic pathway are discussed.

Peptide Modifications: Versatile Tools in Peptide and Natural Product Syntheses

Peptide modifications via C–C bond formation have emerged as valuable tools for the preparation and alteration of non-proteinogenic amino acids and the corresponding peptides. Modification of glycine subunits in peptides allows for the incorporation of unusual side chains, often in a highly stereoselective manner, orchestrated by the chiral peptide backbone. Moreover, modifications of peptides are not limited to the peptidic backbone. Many side-chain modifications, not only by variation of existing functional groups, but also by C–H functionalization, have been developed over the past decade. This account highlights the synthetic contributions made by our group and others to the field of peptide modifications and their application in natural product syntheses.1 Introduction2 Peptide Backbone Modifications via Peptide Enolates2.1 Chelate Enolate Claisen Rearrangements2.2 Allylic Alkylations2.3 Miscellaneous Modifications3 Side-Chain Modifications3.1 C–H Activation3.1.1 Functionalization via Csp3–H Bond Activation3.2.2 Functionalization via Csp2–H Bond Activation3.2 On Peptide Tryptophan Syntheses4 Conclusion

Semi-synthesis and structural elucidation of brevicanines A–D, four new C19-diterpenoid alkaloids with rotameric phenomenon from Aconitum brevicalcaratum

Four new C19-diterpenoid alkaloids brevicanines A–D (1–4) with rotameric phenomenon were isolated from Aconitum brevicalcaratum. They all possessed an unusual axial chiral phenyl-quinazoline side chain and their structures were elucidated by extensive spectroscopic analysis and chemical methods. Meanwhile, brevicanines A and B were semi-synthesized from their parent compound scaconine to further confirm their structures. Variable-temperature NMR spectroscopy was also used to investigate the atropisomers of brevicanine A, in which two sets of signals in 1H NMR spectra were observed at room temperature and coalesced over 140 °C. It's the first time to determine the atropisomeric preference of diterpenoid alkaloids.

ID2007 In vitro selection of macrocyclic peptides against THG-1 for Esophagus Squamous Cell Carcinomas therapeutic lead compounds

Ineffective current treatments for esophagus squamous cell carcinoma (ESCC) is one of the main reasons for its low 5-year survival (20%). Transforming growth factor beta-1 stimulated clone 22 - isoform 4 (Tsc22D4/THG-1) is overexpressed in 92.6% of ESCC specimens while strictly resided in mitotically active basal layer of normal squamous epithelial tissue. Knockout of THG-1 caused reduction in cancer cells growth, invasion and tumorigenesis. Experimentally, protein-protein interactions (PPIs) were identified as THG-1 mechanism to promote cancer progression. Well-known cellular regulators', Keap1, PHD2, TBLR1 and NRBP1, functional interactions are disrupted in the present of THG-1. To develop THG-1 PPIs antagonist, Random non-standard Peptide Integrated Discovery (RaPID) system was employed. In this system, D-stereochemistry, unusual side chains and N- methylation containing macrocyclic peptides was generated and screened against THG-1. High-specificity, flat-surface binding ability, rigidity make those peptides to be more advantageous for PPIs blocking compare to small molecules and antibodies. Herein, I discuss the process to identify potential lead compounds for ESCC therapeutic by blocking THG-1 PPIs.

Topsensterols A-C, Cytotoxic Polyhydroxylated Sterol Derivatives from a Marine Sponge Topsentia sp.

Three new polyhydroxylated sterol derivatives topsensterols A–C (1–3) have been isolated from a marine sponge Topsentia sp. collected from the South China Sea. Their structures were elucidated by detailed analysis of the spectroscopic data, especially the NOESY spectra. Topsensterols A–C (l–3) possess novel 2β,3α,4β,6α-tetrahydroxy-14α-methyl Δ9(11) steroidal nuclei with unusual side chains. Compound 2 exhibited cytotoxicity against human gastric carcinoma cell line SGC-7901 with an IC50 value of 8.0 μM. Compound 3 displayed cytotoxicity against human erythroleukemia cell line K562 with an IC50 value of 6.0 μM.

ChemInform Abstract: Total Synthesis of (‐)‐Exiguolide.

A concise total synthesis of (-)-exiguolide has been completed in an overall 2.8% yield over 20 steps in the longest linear path. The key strategies involve (1) Prins cyclization/homobromination of dienyl alcohol with the B ring-substituted aldehyde, prepared by Prins cyclization/bromination, to construct the A ring with excellent cis-Z stereochemical control and (2) an unusual side chain installation/macrocyclization strategy featuring Sonogashira cross-coupling followed by a ring-closing metathesis reaction to deliver the target.

Total Synthesis of (-)-Exiguolide.

A concise total synthesis of (-)-exiguolide has been completed in an overall 2.8% yield over 20 steps in the longest linear path. The key strategies involve (1) Prins cyclization/homobromination of dienyl alcohol with the B ring-substituted aldehyde, prepared by Prins cyclization/bromination, to construct the A ring with excellent cis-Z stereochemical control and (2) an unusual side chain installation/macrocyclization strategy featuring Sonogashira cross-coupling followed by a ring-closing metathesis reaction to deliver the target.

ChemInform Abstract: Model Foldamers: Applications and Structures of Stable Macrocyclic Peptides Identified Using in vitro Selection

AbstractReview: 46 refs.

Gambierone, a Ladder-Shaped Polyether from the Dinoflagellate Gambierdiscus belizeanus.

A new natural product named gambierone (1) was isolated from the cultured dinoflagellate Gambierdiscus belizeanus. The structure of this compound features an unprecedented polyether skeleton and an unusual right-hand side chain. Its relative configuration was fully determined by interpretation of ROESY experiment and comparison between experimental and theoretical NMR data. Although the succession of cycles has no chemical similarity with ciguatoxins, 1 has a molecular formula and biological activity similar to those of CTX-3C, although much lower in intensity.

Divergolide congeners illuminate alternative reaction channels for ansamycin diversification.

Isolation and structure elucidation of six new divergolides reveal unusual ansamycin diversification reactions including formation of the unusual isobutenyl side chain from a branched polyketide synthase extender unit, azepinone ring closure, macrolide ring contraction and formation of a seco variant by a neighboring group-assisted decarboxylation.

C-17 Lactam-Bearing Limonoids from the Twigs and Leaves of Amoora tsangii

Twelve new lactam-bearing limonoids, amooramides A-L (1-12), were isolated from the twigs and leaves of Amoora tsangii, and their structures fully elucidated by spectroscopic analysis. These compounds represent the first examples of rings A,B-seco-limonoids bearing unusual lactam side chains at C-17, including a 3-substituted 1,5-dihydro-2H-pyrrol-2-one moiety in 1-7 and a 4-substituted 1,5-dihydro-2H-pyrrol-2-one unit in 8-12. Compound 9 inhibited TNFα-induced NF-κB activity by 64% at a concentration of 10 μM.

TbGT8 is a bifunctional glycosyltransferase that elaborates N-linked glycans on a protein phosphatase AcP115 and a GPI-anchor modifying glycan in Trypanosoma brucei

The procyclic form of Trypanosoma brucei expresses procyclin surface glycoproteins with unusual glycosylphosphatidylinositol-anchor side chain structures that contain branched N-acetyllactosamine and lacto-N-biose units. The glycosyltransferase TbGT8 is involved in the synthesis of the branched side chain through its UDP-GlcNAc: βGal β1-3N-acetylglucosaminyltransferase activity. Here, we explored the role of TbGT8 in the mammalian bloodstream form of the parasite with a tetracycline-inducible conditional null T. brucei mutant for TbGT8. Under non-permissive conditions, the mutant showed significantly reduced binding to tomato lectin, which recognizes poly-N-acetyllactosamine-containing glycans. Lectin pull-down assays revealed differences between the wild type and TbGT8 null-mutant T. brucei, notably the absence of a broad protein band with an approximate molecular weight of 110kDa in the mutant lysate. Proteomic analysis revealed that the band contained several glycoproteins, including the acidic ecto-protein phosphatase AcP115, a stage-specific glycoprotein in the bloodstream form of T. brucei. Western blotting with an anti-AcP115 antibody revealed that AcP115 was approximately 10kDa smaller in the mutant. Enzymatic de-N-glycosylation demonstrated that the underlying protein cores were the same, suggesting that the 10-kDa difference was due to differences in N-linked glycans. Immunofluorescence microscopy revealed the colocalization of hemagglutinin epitope-tagged TbGT8 and the Golgi-associated protein GRASP. These data suggest that TbGT8 is involved in the construction of complex poly-N-acetyllactosamine-containing type N-linked and GPI-linked glycans in the Golgi of the bloodstream and procyclic parasite forms, respectively.