Covering: 2012 to 2018
The principles and applicability of optical rotation, and electronic and vibrational circular dichroism aided by quantum chemical calculations are presented to determine ...absolute configuration and conformation through examples of stereochemical analysis of natural products with emphasis on the possibility of combined analysis and pitfalls for natural product chemists.
OR, ECD and VCD are powerful methods to determine the absolute configuration of natural products either applied independently or in combination.
Four new cladosporol derivatives, cladosporols F–I (1–4), the known cladosporol C (5), and its new epimer, cladosporol J (6), were isolated and identified from the marine algal-derived endophytic ...fungus Cladosporium cladosporioides EN-399. Their structures were determined by detailed interpretation of NMR and MS data, and the absolute configurations were established on the basis of TDDFT-ECD and OR calculations. The configurational assignment of cladosporols F (1) and G (2) showed that the previously reported absolute configuration of cladosporol A and all the related cladosporols need to be revised from (4′R) to (4′S). Compounds 1–6 showed antibacterial activity against Escherichia coli, Micrococcus luteus, and Vibrio harveyi with MIC values ranging from 4 to 128 μg/mL. Compound 3 showed significant cytotoxicity against A549, Huh7, and LM3 cell lines with IC50 values of 5.0, 1.0, and 4.1 μM, respectively, and compound 5 showed activity against H446 cell line with IC50 value of 4.0 μM.
The absolute configuration of psammaplysin A (1) has been assigned as (6R,7R) using experimental and calculated electronic circular dichroism (ECD) data and NMR analysis of MPA esters prepared from ...the acetamide derivative of 1. Detailed conformational analyses of a truncated model compound of 1 with an in vacuo method and with the PCM solvent model for MeOH have identified the major conformers and factors governing the ECD spectrum of 1. The correlation of the ECD data with the stereochemistry of 1 allows configurational assignment of related psammaplysin analogues on the basis of their ECD spectra.
LC–MS-oriented fractionation of the sponge Aaptos suberitoides resulted in the isolation of four heptacyclic alkaloids, aaptodines A–D (1–4), which contain ...9,10-dihydrofuro2,3-f1,3oxazolo5,4-hquinolone and 7,8-dihydrocyclopentade1,6naphthyridine subunits with a spiro carbon atom. The structures were determined on the basis of NMR spectroscopic and single-crystal X-ray diffraction data analysis aided by electronic circular dichroism calculations and Mosher’s method. A biosynthetic pathway for the formation of aaptodines A–D is postulated. Aaptodine D exhibits potent inhibition against osteoclast formation.
Three novel heterodimeric laurane-type sesquiterpenoids, laurokamurols A–C (1–3), along with eight known related monomeric ones (4–11) were isolated from the East China Sea red alga Laurencia ...okamurai Yamada. The absolute configurations of the new bis-sesquitepenoids, especially their axial chirality, were determined by extensive spectroscopic analyses and TDDFT-ECD method. All of the new compounds showed promising PTP1B inhibitory activities with IC50 values comparable to the positive control, indicating them as potential food additives or pharmaceutical drug leads toward obesity or diabetes.
Four new diketopiperazines including spirobrocazines A–C (1–3) and brocazine G (4) were characterized from the mangrove-derived Penicillium brocae MA-231. Compounds 1 and 2 had a 6/5/6/5/6 cyclic ...system with a rare spirocyclic center at C-2. Their structures and absolute configurations were determined by spectroscopic analysis, TDDFT-ECD calculations, and X-ray diffraction. Compound 4 exhibited potent cytotoxicity against both sensitive and cisplatin-resistant human ovarian cancer cells and strong antimicrobial activity against pathogenic Staphylococcus aureus.
Alternarin A (1), a rearranged drimane meroterpenoid characterized by a thioglycerate moiety, was isolated together with two known analogues from the coral-associated fungi Alternaria sp. ZH-15. Its ...structure was determined based on spectroscopic analysis, modified Mosher’s method, and TDDFT/ECD calculations. In a primary cultured cortical neuronal network, compound 1 effectively inhibited the activity of spontaneous synchronous Ca2+ oscillations and 4-aminopyridine induced epileptic discharges in the low micromolar concentration range.
Fourteen new natural products, namely, 2-(Z)-styryl-5-geranylresorcin-1-carboxylic acid (1), amorfrutin D (2), 4-O-demethylamorfrutin D (3), 8-geranyl-3,5,7-trihydroxyflavanone (4), ...8-geranyl-5,7,3′-trihydroxy-4′-methoxyisoflavone (5), 6-geranyl-5,7,3′-trihydroxy-4′-methoxyisoflavone (6), 8-geranyl-7,3′-dihydroxy-4′-methoxyisoflavone (7), 3-O-demethyldalbinol (8), 6a,12a-dehydro-3-O-demethylamorphigenin (9), (6aR,12aR,5′R)-amorphigenin (10), amorphispironones B and C (11 and 12), resokaempferol 3-O-β-d-glucopyranosyl-(1→2)-β-d-glucopyranoside-7-O-α-l-rhamnopyranoside (13), and daidzein 7-O-β-d-glucopyranosyl-(1→2)-β-d-glucopyranoside (14), together with 40 known compounds, were isolated from the fruits of Amorpha fruticosa. The structures of the new compounds were elucidated by 1D and 2D NMR spectroscopic analysis as well as from the mass spectrometry data. ECD calculations were performed to determine the absolute configurations of 11 and 15. Compounds 1, 4–6, and 16–23 showed potent to moderate antibacterial activities against several Gram-positive bacteria with MIC values ranging from 3.1 to 100 μM. In addition, compounds 11 and 24–33 were significantly cytotoxic against the L5178Y mouse lymphoma cell line and exhibited IC50 values from 0.2 to 10.2 μM.
Dendrodolides A–M (1–13), 13 new 12-membered macrolides, were isolated from Dendrodochium sp., a fungus associated with the sea cucumber Holothuria nobilis Selenka, which was collected from the South ...China Sea. The structures of the dendrodolides were elucidated by means of detailed spectroscopic analysis and X-ray single-crystal diffraction. The absolute configurations were assigned using the modified Mosher method, exciton-coupled circular dichroism (ECCD), electronic solution and solid-state circular dichroism (ECD) supported by time-dependent density functional theory (TDDFT) ECD calculations, and X-ray analysis. A detailed conformational analysis of the 13 derivatives indicated that the conformation of the flexible macrolide ring plays a decisive role in their chiroptical properties. Thus, it is highly recommended to apply advanced levels of theory and to avoid simple comparison of ECD spectra to determine the absolute configurations of these derivatives. In an in vitro bioassay, compounds 1–5, 7–9, 11, and 12 exhibited different levels of growth inhibitory activity against SMMC-7721 and HCT116 cells. This is the first report of 12-membered macrolides from the fungus of the genus Dendrodochium. The coisolation of four pairs of epimers is extremely interesting and indicates the complexity of β-ketoreductase stereospecificity in the biosynthesis of enigmatic iterative fungal polyketides.
Four tetrahydroxanthone dimers (1–4) and four biogenetically related monomers (5–8), including the new derivatives 4–6, were isolated from the endophyte Phomopsis longicolla. The absolute ...configurations of 2–4 were established for the first time by TDDFT electronic circular dichroism calculations, and that of phomoxanthone A (1) was revised by X-ray crystallography. Phomoxanthone A (1) showed the strongest pro-apoptotic activity when tested against a panel of human cancer cell lines, including cisplatin-resistant cells, whereas it was up to 100-fold less active against healthy blood cells. It was also the most potent activator of murine T lymphocytes, NK cells, and macrophages, suggesting an activation of the immune system in parallel to its pro-apoptotic activity. This dual effect in combating cancer cells could help in fighting resistance during chemotherapy. Preliminary structure–activity studies of isolated compounds and derivatives obtained by semisynthesis (9a–11) hinted at the location of the biaryl axis and the presence of acetyl groups as important structural elements for the biological activity of the studied tetrahydroxanthones.
