Analysis of chemical constituents from Polygonatum cyrtonema after “Nine-Steam-Nine-Bask” processing

Seven new compounds, known as polygonatine N₁‒N₇ (1‒7), and a known compound (8) were isolated from the ‘Nine-Steam-Nine-Bask’ processing product of Polygonatum cyrtonema Hua. The compounds’ structures were determined by spectroscopic analysis. All compounds were tested for dipeptidyl peptidase-4 (DPP-4) inhibition, glucose transport, and anti-inflammatory activities. Compound 8 suppressed NO production with an IC₅₀ of 35.4 μM.     

6-Gingerol and Semisynthetic 6-Gingerdione Counteract Oxidative Stress Induced by ROS in Zebrafish

6-Gingerol ( 1 ) is one of the major components in ginger and developing new synthetic methodologies could bring semisynthetic analogs with improved therapeutic properties. Towards this, multigram scale isolation of 6-gingerol with excellent purity was optimized using a simple and robust extraction, followed by column purification. Synthesis of 6-gingerdione, 7 from 6-gingerol was then achieved through selective –OTBDMS protection, DMP oxidation and deprotection reaction sequence for the first time. Compounds 1 , 7 and 8 (dehydrozingerone) exhibited excellent cell-free antioxidant properties in DPPH, ABTS, superoxide radical scavenging assay and H₂O₂ assay at 10–50 μM concentrations. The hemolytic study suggests that up to 50 μM, all three compounds did not exhibit toxicity to human erythrocytes. When H₂O₂ treated zebrafish larvae groups (96hpf) were exposed to compounds 1 , 7 and 8 , it increases the SOD (19, 19.1 and 18.7 U/mg protein), CAT (18.1, 16.5, and 15.8 μmol/mg levels and decreases the lipid peroxidation level (13, 15 and 18 nmol/mg protein), respectively. In vivo ROS levels and degree of cell death were studied using DCFDA and Acridine orange assays. Compounds 1 , 7 and 8 decreases the ROS and cell death level significantly. Taken together, compounds 1 , 7 and 8 exhibit excellent antioxidant properties, counteract H₂O₂ induced oxidative stress, reduces cell death in zebrafish larvae.     

Antiprotozoal activities of marine polyether triterpenoids

Chagas disease and leishmaniasis are tropical neglected diseases caused by kinetoplastids protozoan parasites of Trypanosoma and Leishmania genera, and a public health burden with high morbidity and mortality rates in developing countries. Among difficulties with their epidemiological control, a major problem is their limited and toxic treatments to attend the affected populations; therefore, new therapies are needed in order to find new active molecules. In this work, sixteen Laurencia oxasqualenoid metabolites, natural compounds 1–11 and semisynthetic derivatives 12–16, were tested against Leishmania amazonensis, Leishmania donovani and Trypanosoma cruzi. The results obtained point out that eight substances possess potent activities, with IC₅₀ values in the range of 5.40–46.45 µM. The antikinetoplastid action mode of the main metabolite dehydrothyrsiferol (1) was developed, also supported by AFM images.The semi-synthetic active compound 28-iodosaiyacenol B (15) showed an IC₅₀ 5.40 µM against Leishmania amazonensis, turned to be non-toxic against the murine macrophage cell line J774A.1 (CC₅₀ > 100). These values are comparable with the reference compound miltefosine IC₅₀ 6.48 ± 0.24 and CC₅₀ 72.19 ± 3.06 μM, suggesting that this substance could be scaffold for development of new antikinetoplastid drugs.     

Chemical transformation and biological studies of marine sesquiterpene (S)-(+)-curcuphenol and its analogs

Chemical transformation studies of the marine sesquiterpene phenol (S)-(+)-curcuphenol (1), isolated from the Jamaican sponges Myrmekioderma styx, were accomplished. In order to optimize the activity and better understand the SAR of (S)-(+)-curcuphenol, nineteen semisynthetic analogs were prepared and evaluated for activity against infectious diseases. A number of analogs showed significant activity against Mtb and Leishmania donovani, while showed good to moderate activities in antibacterial and antifungal assays as well as against Plasmodium falciparium (D6 clone) and (W2 clone). The analogs a, c, h, and r exhibited Mtb activity with MICs of 24.6, 41.2, 6.90, and 50.5 μM, respectively. Analog f showed enhanced activity against L. donovani with an IC₅₀ of 0.6 μM and IC₉₀ of 40 μM respectively.     

Antiproliferative homoscalarane sesterterpenes from two Madagascan sponges

Dereplication of the antiproliferative ethyl acetate fraction of the Madagascan sponge Carteriospongia sp. led to the detection and isolation of the two known homoscalarane-type sesterterpenes 1 and 2. Investigation of a similar sponge containing closely related compounds afforded the four new antiproliferative homoscalarane sesterterpenes (3 and 5?7). The structures of all isolated compounds were elucidated by spectroscopic methods, including UV, IR and 1D and 2D NMR. Compounds 1, 3 and 5 displayed submicromolar antiproliferative activity against the A2780 ovarian cell line with IC₅₀ values of 0.65, 0.26 and 0.28 μM, respectively, while compounds 6 and 7 showed moderate activity (4.5 and 8.7 μM, respectively). Compounds 3 and 5 also displayed anti-proliferative activity against the H522-T1 non-small cell lung and A2058 human melanoma cancer cell lines.     

Evaluation of single and joint effect of metabolites isolated from marine sponges,Fasciospongia cavernosa and Axinella donnani on antimicrobial properties

The biochemical mechanisms that marine sponges have developed as a chemical defense to protect themselves against micro and subsequent macrobiofouling process might comprise a potential alternative for the preventing attack of biofilm forming bacteria. The present study investigated the antimicrobial activity of a series of major secondary metabolites isolated from the sponges Fasciospongia cavernosa and Axinella donnani against fouling bacteria. Secomanoalide (1), dehydromanoalide (2) and cavernosine (3) have been isolated from F. cavernosa. Their structures were determined by MS, ¹H NMR spectra analyses and by comparison with those reported in the literature. The most promising activity was exhibited by the metabolites from A. donnani, that is, cerebroside (5) against three strains Aeromonas hydrophila subsp. salmonicida A449 and Erythrobacter litoralis. Our investigation revealed that combined metabolites 1, 2 and 3 retained strong activity but individual metabolite had moderate activity indicating that activity probably results from synergistic interactions between multiple compounds. The antibacterial screening of compounds 3, 5 and synergistic effect of 1–3 against fouling bacteria has been studied for the first time. Further, isolation of manoalide related compounds and their synergistic screening can be accelerated for the development of new biofilm inhibitors.     

Discovery of new A- and B-type laxaphycins with synergistic anticancer activity

Two new cyclic lipopeptides termed laxaphycins B4 (1) and A2 (2) were discovered from a collection of the marine cyanobacterium Hormothamnion enteromorphoides, along with the known compound laxaphycin A. The planar structures were solved based on a combined interpretation of 1D and 2D NMR data and mass spectral data. The absolute configurations of the subunits were determined by chiral LC-MS analysis of the hydrolysates, advanced Marfey’s analysis and 1D and 2D ROESY experiments. Consistent with similar findings on other laxaphycin A- and B-type peptides, laxaphycin B4 (1) showed antiproliferative effects against human colon cancer HCT116 cells with IC₅₀ of 1.7?µM, while laxaphycins A and A2 (2) exhibited weak activities. The two major compounds isolated from the sample, laxaphycins A and B4, were shown to act synergistically to inhibit the growth of HCT116 colorectal cancer cells.     

Three New Cytotoxic Acylspermidines from the Soft Coral,Sinularia sp.

Three new acylated spermidines and two known related compounds were isolated from the Okinawan soft coral, Sinularia sp. These compounds were N′,N″,N″-trimethylspermidines that are acylated by a methyl-branched unsaturated fatty acid. These acylspermidines showed potent cytotoxicity against human tumor cell lines at an IC₅₀ value of 17 ng/ml and the induction of apoptotic phenomena.     

Semi-synthesis of oxygenated dolabellane diterpenes with highly in vitro anti-HIV-1 activity

Research on dolabellane diterpenes of brown algae Dictyota spp. has shown that these diterpenoids have strong anti-HIV-1 activity, but there are not data about antiviral activity of dolabellane diterpenes isolated from octocorals, which are antipodes of those isolated from the brown algae. Dolabellanes 13-keto-1(R),11(S)-dolabella-3(E),7(E),12(18)-triene (1) and β-Araneosene (2) were isolated from the Caribbean octocoral Eunicea laciniata, and both showed low anti-HIV-1 activity and low toxicity. Since it was shown that oxygenated dolabellanes from algae have better anti-HIV-1 activity, in this work some derivatives of the main dolabellane of E. laciniata 1 were obtained by epoxidation (3), epoxide opening (4), and allylic oxidation (5). The derivatives showed significant improvement in the anti-HIV-1potency (100-fold), being compounds 3 and 5 the most active ones. Their high antiviral activities, along with their low cytotoxicity, make them promissory antiviral compounds; and it is worth noting that the absolute configuration at the ring junction in the dolabellane skeleton does not seem to be determinant in the antiviral potency of these diterpeneoids.     

Mini-review: Marine natural products and their synthetic analogs as antifouling compounds: 2009–2014

This review covers 214 marine natural compounds and 23 of their synthetic analogs, which were discovered and/or synthesized from mid-2009 to August 2014. The antifouling (AF) compounds reported have medium to high bioactivity (with a threshold of EC₅₀ < 15.0 mg ml^?1). Among these compounds, 82 natural compounds were identified as new structures. All the compounds are marine-derived, demonstrating that marine organisms are prolific and promising sources of natural products that may be developed as environmentally friendly antifoulants. However, this mini-review excludes more than 200 compounds that were also reported as AF compounds but with rather weak bioactivity during the same period. Also excluded are terrestrial-derived AF compounds reported during the last five years. A brief discussion on current challenges in AF compound research is also provided to reflect the authors’ own views in terms of future research directions.     

Synthesis and paroxonase activities of novel bromophenols

Three novel bromophenols 10–12 were synthesized. Acylation of veratrole (4) with 2,3-dimethoxy benzoic acid (5) gave a kown diarylmethanone 6. Bromination of 6 with different equivalents of molecular bromine afforded new di and tribrominated compounds 7–9 which were converted to their corresponding bromophenols 10–12 via O-demethylation with BBr₃. Paraoxonase-1 (PON1) was purified from human serum with approximately 42% and 3584?U × mg^?1 specific activity. The synthesized compounds 6–12 showed inhibitory effects on paraoxonase-1 (PON1) which is an organophosphate (OP) hydrolyser and an antioxidant bioscavenger enzyme. IC₅₀ values were determined in the range of 0.123–1.212?mM.

Graphical abstract

     

Nature-inspired pyrrolo[2,3-d]pyrimidines targeting the histamine H3 receptor

Inspired by marine compounds the derivatization of the natural pyrrolo[2,3-d]pyrimidine lead scaffold led to a series of novel compounds targeting the histamine H₃ receptor. The focus was set on improved binding towards the receptor and to establish an initial structure-activity relationship for this compound class based on the lead structure (compound V, K_i value of 126 nM). As highest binding affinities were found with 1,4-bipiperidines as basic part of the ligands, further optimization was focused on 4-([1,4′-bipiperidin]-1′-yl)-pyrrolo[2,3-d]pyrimidines. Related pyrrolo[2,3-d]pyrimidines that were isolated from marine sponges like 4-amino-5-bromopyrrolo[2,3-d]pyrimidine (compound III), showed variations in halogenation pattern, though in a next step the impact of halogenation at 2-position was evaluated. The chloro variations did not improve the affinity compared to the dehalogenated compounds. However, the simultaneous introduction of lipophilic cores with electron-withdrawing substitution patterns in 7-position and dehalogenation at 2-position (11b, 12b) resulted in compounds with significantly higher binding affinities (K_i values of 7 nM and 6 nM, respectively) than the initial lead structure compound V. The presented structures allow for a reasonable structure-activity relationship of pyrrolo[2,3-d]pyrimidines as histamine H₃ receptor ligands and yielded novel lead structures within the natural compound library against this target.     

Comparative sequence analysis of bacterial symbionts from the marine sponges Geodia cydonium and Ircinia muscarum

Marine sponges (Porifera) live in a symbiotic relationship with microorganisms, primarily bacteria. Recently, several studies indicated that sponges are the most prolific source of biologically-active compounds produced by symbiotic microorganisms rather than by the sponges themselves. In the present study we characterized the bacterial symbionts from two Demospongiae, Ircinia muscarum and Geodia cydonium. We amplified 16S rRNA by PCR, using specific bacterial-primers. The phylogenetic analysis revealed the presence of nine bacterial clones from I. muscarum and ten from G. cydonium. In particular, I. muscarum resulted enriched in Bacillus species and G. cydonium in Proteobacterium species. Since these bacteria were able to produce secondary metabolites with potential biotechnological and biopharmaceutical applications, we hypothesized that I. muscarum and G. cydonium could be a considered as a “gold mine” of natural products.     

Natural urease inhibitors from Aloe vera resin and Lycium shawii and their structural-activity relationship and molecular docking study

Bio-assay guided fractionation of the methanolic extract of Aloe vera resin and Lycium shawii stem successively afforded twenty three compounds; fourteen (1–14) from A. vera and nine (15–23) from L. shawii. All these compounds were characterized by 1D and 2D NMR spectroscopic techniques viz., ¹H, ¹³C, DEPT, HSQC, HMBC, and COSY, and NEOSY, ESI-MS and compared with the reported literature. These compounds were assessed for their potential as urease inhibitors targeted in peptic ulcer. Among crude extracts and fractions of A. vera resin, n-butanol fraction (23.5 ± 1.7 μg·mL⁻¹) showed the most potent urease inhibition followed by methanol (30.9 ± 0.3 μg/mL) and ethyl acetate (31.7 ± 0.5 μg·mL⁻¹). In case of L. shawii, ethyl acetate fraction exhibited the highest urease activity (41.0 ± 1.4 μg/mL) trailed by dichloromethane (55.2 ± 1.5 μg/mL) fraction. Among the isolates, compounds 7, 11 and 23 were found to be excellent urease inhibitors with IC₅₀ values of 14.5 ± 0.90 µM, (16.7 ± 0.16 µM) and 14.0 ± 0.8 µM, respectively. To the best of our knowledge, this is the first report on the urease enzyme inhibitory activity of the said compounds excluding compound 18. In addition, the urease activity of different fractions of L. shawii stem was also reported for the first time. The molecular docking studies showed that all the active compounds well accommodate in the active site of the urease enzyme by interacting with key amino acids.     

Stepwise Frontal Analysis Coupled with Affinity Chromatography: A Fast and Reliable Method for Potential Ligand Isolation and Evaluation from Mahuang-Fuzi-Xixin Decoction

Mahuang-Fuzi-Xixin Decoction (MFXD) is widely used in the treatment of asthma, however, the functional components in the decoction targeting beta2-adrenoceptor (β₂-AR) remain unclear. Herein, we immobilized the haloalkane dehalogenase (Halo)-tagged β₂-AR on the 6-chlorocaproic acid-modified microspheres. Using the affinity stationary phase, the interactions of four ligands with the receptor were analyzed by stepwise frontal analysis. The association constants were (4.75±0.28)×10⁴ M⁻¹ for salbutamol, (2.93±0.15)×10⁴ M⁻¹ for terbutaline, (1.23±0.03)×10⁴ M⁻¹ for methoxyphenamine, (5.67±0.38)×10⁴ M⁻¹ for clorprenaline at high-affinity binding site, and (2.73±0.05)×10³ M⁻¹ at low-affinity binding site. These association constants showed the same rank order as the radioligand binding assay, demonstrating that immobilized β₂-AR had capacity to screen bioactive compounds binding to the receptor while stepwise frontal analysis could predict their binding affinities. Application of the immobilized receptor in analysis of MFXD by chromatographic method revealed that ephedrine, aconifine, karakoline, and chasmanine were the bioactive compounds targeting β₂-AR. Among them, ephedrine and chasmanine exhibited association constants of (2.94±0.02)×10⁴ M^-1and (4.60±0.15)×10⁴ M⁻¹ to the receptor by stepwise frontal analysis. Molecular docking analysis demonstrated that ephedrine, chasmanine, and the other two compounds interact with β₂-AR through the same pocket involving the key amino acids such as Asn312, Asp113, Phe289, Trp286, Tyr316, and Val114. As such, we reasoned that the four compounds dominate the therapeutic effect of MFXD against asthma through β₂-AR mediating pathway. This work shed light on the potential of immobilized β₂-AR for drug discovery and provided a valuable methodology for rapid screening.     

Profiling Auspicious Butyrylcholinesterase Inhibitory Activity of Two Herbal Molecules: Hyperforin and Hyuganin C

Cholinergic therapy based on cholinesterase (ChE) inhibitory drugs is the mainstay for the treatment of Alzheimer's disease. Therefore, an extensive research has been continuing for the discovery of drug candidates as inhibitors of acetyl‐ and butyrylcholinesterase. In this study, two natural molecules, e. g. hyperforin and hyuganin C were tested in vitro for their AChE and BChE inhibitory activity. Both of the compounds were ineffective against AChE, whereas hyperforin (IC₅₀=141.60±3.39 μm ) and hyuganin C (IC₅₀=38.86±1.69 μm ) were found to be the highly active inhibitors of BChE as compared to galantamine (IC₅₀=46.58±0.91 μm ) which was used as the reference. Then, these molecules were further proceeded to molecular docking experiments in order to establish their interactions at the active site of BChE. The molecular docking results indicated that both of them are able to block the access to key residues in the catalytic triad of the enzyme, while they complement some of the hydrophobic residues of the cavity, what is consistent with our in vitro data. While both compounds were predicted as mutagenic, only hyuganin C showed hepatotoxicity in in silico analysis. According to whole outcomes that we obtained, particularly hyuganin C besides hyperforin are the promising BChE inhibitors, which can be the promising compounds for AD therapy.     

Polyoxygenated ent-kauranes and water-soluble conjugates in seed of Phaseolus coccineus

C-α and C-β, previously isolated from seed of Phaseolus coccineus, are shown respectively to be the bis-O-isopropylidene and the 16,17-mono-O-isopropylidene derivatives of ent-6α,7α,16β,17-tetrahydroxykauranoic acid. By GC-MS characterization of the products of acidic, basic and enzymatic hydrolysis, water soluble conjugates of the following compounds have been shown to occur in P. coccineus seed: GA₈, GA₁₇, GA₂₀, GA₂₈, ent-6α,7α,13-trihydroxykaurenoic acid, ent-6α,7α,17-trihydroxy-16β-kauranoic acid, ent-6α,7α,16β,17-tetrahydroxykauranoic acid, 7β,13-dihydroxykaurenolide and abscisic acid.     

One-step partial synthesis of (±)-asperteretone B and related hPTP1B1–400 inhibitors from butyrolactone I

Protein tyrosine phosphatase 1B (PTP1B) is a validated target for developing antiobesity, antidiabetic and anticancer drugs. Over the past years, several inhibitors of PTP1B have been discovered; however, none has been approved by the drug regulatory agencies. Interestingly, the research programs focused on discovering PTP1B inhibitors typically use truncated structures of the protein (PTP1B_1-300, 1–300 amino acids), leading to the loss of valuable information about the inhibition and selectivity of ligands and repeatedly misleading the optimization of putative drug leads. Up to date, only six inhibitors of the full-length protein (hPTP1B_1-400), with affinity constants ranging from 1.3 × 10⁴ to 3.3 × 10⁶ M⁻¹, have been reported. Towards the discovery of new ligands of the full-length human PTP1B (hPTP1B_1-400) from natural sources, herein we describe the isolation of a γ-lactone (1, butyrolactone I) from the fungus Aspergillus terreus, as well as the semisynthesis, inhibitory properties (in vitro and in silico), and the structure-activity relationship of a set of butyrolactone derivatives (1 and 2, and 6–12) as hPTP1B_1-400 inhibitors, as well as the affinity constant (k_a = 2.2 × 10⁵ M⁻¹) of the 1-hPTP1B₁–₄₀₀ complex, which was determined by fluorescence quenching experiments, after the inner filter effect correction.     

LC-NMR: a new tool to expedite the dereplication and identification of natural products

The rapid identification of known or undesirable compounds from natural products extracts — “dereplication” — is an important step in an efficiently run natural products discovery program. Dereplication strategies use analytical techniques and database searching to determine the identity of an active compound at the earliest possible stage in the discovery process. In the past few years, advances in technology have allowed the development of tandem analytical techniques such as liquid chromatography mass spectrometry (LC-MS), LC-MS-MS, liquid chromatography nuclear magnetic resonance (LC-NMR), and LC-NMR-MS. LC-NMR, despite its lower sensitivity as compared to LC-MS, provides a powerful tool for rapid identification of known compounds and identification of structure classes of novel compounds. LC-NMR is especially useful in instances where the data from LC-MS are incomplete or do not allow confident identification of the active component of a sample. LC-NMR has been used to identify the marine alkaloid aaptamine as the active component in an extract of the sponge Aaptos sp. This extract had been identified as an enzyme inhibitor by a high throughput screening (HTS) effort. Isolated aaptamine exhibited an IC₅₀=120 μM against this enzyme. Strategies for the identification of aaptamine and for the use of LC-NMR in a natural products HTS program are discussed. Journal of Industrial Microbiology & Biotechnology (2000) 25, 342–345. Received 30 March 2000/ Accepted in revised form 03 July 2000     

Flavonoids from chemotypes of the goldback fern, Pityrogramma triangularis

More than 20 flavonoid aglycones were identified from the frond exudate of various collections of Pityrogramma triangularis. Ten of them are novel natural products; most of the others are rare flavonoids. They are substituted at C-8; many are C-methylated. They mostly occur only as trace constituents in var. triangularis. Two compounds come from var. viscosa. One population of P. triangularis var. triangularis exhibits a unique flavonoid pattern not encountered before in any other chemotype studied.