Dihydrochalcones from lindera umbellata

Two dihydrochalcones, 2′,6′-dihydroxy-4′-methoxydihydrochalcone and 2,4′,6′-trihydroxydihydrochalcone have been isolated from leaves of Lindera umbellata.     

Six 2′-hydroxyflavonols from Gutierrezia microcephala

Six 2′-hydroxyflavonols were isolated from Gutierrezia microcephala, including four new compounds, 5,7,2′-trihydroxy-3,6,4′,5′-tetramethoxyflavone, 5,7,2′-trihydroxy-3,6,8,4′,5′-pentamethoxyflavone, 5,2′-dihydroxy-3,6,7,8,4′,5′-hexamethoxyflavone and 5,7,2′,4′-tetrahydroxy-3,8,5′-trimethxoyflavone and two known compounds, 5,7,2′,5′-tetrahydroxy-3,6,8,4′-tetramethoxyflavone and 5,7,2′,4′-tetrahydroxy-3,6,8,5′-tetramethoxyflavone.     

Octasubstituted flavones from Ageratum houstonianum

Two new highly oxygenated flavones, were isolated from aerial parts of Ageratum houstonianum. Their structures were established as 3′-hydroxy-5,6,7,8,2′,4′,5′-heptamethoxyflavone and 5,3′-dihydroxy-6,7,8,2′,4′,5′-hexamethoxyflavone on the basis of spectral data and chemical degradation. The structure of the latter compound was confirmed by X-ray analysis.     

Flavonoids of Gardenia cramerii and G. fosbergii bud exudates

From the bud exudates of Gardenia cramerii and G. fosbergii, two species endemic to Sri Lanka, a new flavonoid with an unusual B-ring oxidation pattern, 5,5′-dihydroxy-6,7,2′,3′-tetramethoxyflavone, was characterized. Two other rare flavonoids, 5,3′,5′-trihydroxy-3,6,7,4′-tetramethoxyflavone and 5-hydroxy-6,7,3′,4′,5′-pentamethoxyflavone were also isolated from both Gardenia species.     

Two new C-methylated flavonoids from Myrica gale

From the leaves of Myrica gale 2′,4′-dihydroxy-6′-methoxy-3′,5′-dimethylchalcone has been isolated. The fruits yielded 2′-hydroxy-4′,6′-dimethoxy-3′-methyldihydrochalcone. The constitutions were deduced from spectroscopic data and confirmed by synthesis.     

Methoxyspheroidene and methoxyspheroidenone,two carotenoids from Rhodopseudomonas spheroides

Two new carotenoids isolated from Rhodopseudomonas spheroides (Rhodospirillaceae) have been identified as methoxyspheroidene (1,1′-dimethoxy-3,4-didehydro-1,2,1′,2′,7$\text{,}\text{?}$8′-hexahydro-ψ,ψ-carotene) obtained from anaerobic cultures and methoxyspheroidenone (1,1′-dimethoxy-3,4-didehydro-1,2,1′,2′,7′,8′-hexahydro-ψ,ψ-caroten-2-one) recovered from aerobic cultures.     

Chalcone glycosides of Antirrhinum majus

Three chalcones have been found in yellow flowers of A. majus, two of which have been identified as chalcononaringenin 4′-glucoside and 3,4,2′,4′,6′-pentahydroxychalcone 4′-glucoside.     

Interaction between flavins and alcohols

The effect of alcohols on the spectral properties of riboflavin derivatives in non-polar solvent was studied by various spectroscopic methods in order to support the view point that alcohol may directly interact with the isoalloxazine moiety of FAD and enhance the catalytic activity of D-amino acid oxidase (DAAO). The most likely association complex between alcohol and riboflavin is 1 : 1 stoichiometric complex through the 3-N imino and the 2-C carbonyl groups of the isoalloxazine ring and the hydroxyl group of alcohols. It appears that methanol has a larger association constant than any other alcohols, and the association constant decreases with the increase in carbon number and with the steric requirement of the alkyl group of alcohols.     

In vivo binding of 2,3,6,2′,3′,6′-hexachlorobiphenyl and 2,4,5,2′,4′,5′-hexachlorobiphenyl to mouse liver macromolecules

The role of metabolic activation in the binding of polychlorinated biphenyls (PCBs) to cellular macromolecules was investigated in vivo by comparing the relative binding of 2,4,5,2′,4′,5′-[U-¹⁴C]hexachlorobiphenyl (2,4,5), a slowly metabolized PCB, with that of 2,3,6,2′,3′,6′-[U-¹⁴C]hexachlorobiphenyl (2,3,6), a rapidly metabolized PCB, and the appropriate controls. Each hexachlorobiphenyl was administered to mice, orally for 5 days (7.28 mg/kg/day). Following the dosing schedule, animals were killed at 1, 5 and 8 days. The concentration of each PCB was determined in liver, muscle and kidney and in purified macromolecules isolated from those tissues. The concentration of 2,4,5 was consistently higher than the concentration of 2,3,6 in all tissues studied. However, the amount of 2,3,6 bound to the purified macromolecules was consistently at least one order of magnitude greater than that of 2,4,5. The greatest binding was observed in RNA followed by protein and DNA, respectively. The purity of the macromolecules and the presence of PCB-derived radioactivity at the monomer level were confirmed. This is the first report of ¹⁴C-labeled PCB being bound to purified RNA, DNA, and proteins isolated from the tissues of animals treated in vivo. The binding is thought to be covalent and to be the result of metabolic activation.     

Flavones from Eupatorium leucolepis

Chloroform extraction of Eupatorium leucolepis gave the new flavones 3′-hydroxy-5,6,7,8,4′,5′-hexamethoxyflavone, 4′-hydroxy-5,6,7,8,3′,5     

Flavans from Zephyranthes flava

A new optically active flavan aglucone, 7-hydroxy-3′,4′-methylenedioxyflavan, and its 7-glucoside have been isolated from the bulbs of Zephyranthes flava, collected at flowering. Additionally, two known flavans, 7,4′-dihydroxy-3′-methoxyflavan and 7-methoxy-2′-hydroxy-4′,5′-methylenedioxyflavan, have been isolated for the first time from this species. The structures of these flavans have been established by comprehensive analyses (UV, IR, ¹H NMR, ¹³C NMR, mass spectrometry, [α]_D) of the compounds and their acetates, and also by chemical correlation.     

Inhibition of thymidylate synthase by 2′,2′-difluoro-2′-deoxycytidine (Gemcitabine) and its metabolite 2′,2′-difluoro-2′-deoxyuridine

2′,2′-Difluoro-2′-deoxycytidine (dFdC, gemcitabine) is a cytidine analogue active against several solid tumor types, such as ovarian, pancreatic and non-small cell lung cancer. The compound has a complex mechanism of action. Because of the structural similarity of one metabolite of dFdC, dFdUMP, with the natural substrate for thymidylate synthase (TS) dUMP, we investigated whether dFdC and its deamination product 2′,2′-difluoro-2′-deoxyuridine (dFdU) would inhibit TS. This study was performed using two solid tumor cell lines: the human ovarian carcinoma cell line A2780 and its dFdC-resistant variant AG6000. The specific TS inhibitor Raltitrexed (RTX) was included as a positive control. Using the in situ TS activity assay measuring the intracellular conversion of [5-³H]-2′-deoxyuridine or [5-³H]-2′-deoxycytidine to dTMP and tritiated water, it was observed that dFdC and dFdU inhibited TS. In A2780 cells after a 4 h exposure to 1 μM dFdC tritium release was inhibited by 50% but did not increase after 24 h, Inhibition was also observed following dFdU at 100 μM. No effect was observed in the dFdC-resistant cell line AG6000; in this cell line only RTX had an inhibitory effect on TS activity. In the A2780 cell line RTX inhibited TS in a time dependent manner. In addition, DNA specific compounds such as 2′-C-cyano-2′-deoxy-1-beta-D-arabino-pentafuranosylcytosine and aphidicoline were utilized to exclude DNA inhibition mediated down regulation of the thymidine kinase.Inhibition of the enzyme resulted in a relative increase of mis-incorporation of [5-³H]-2′-deoxyuridine into DNA. In an attempt to elucidate the mechanism of in situ TS inhibition the ternary complex formation and possible inhibition in cellular extracts of A2780 cells, before and after exposure to dFdC, were determined. With the applied methods no proof for formation of a stable complex was found. In simultaneously performed experiments with 5FU such a complex formation could be demonstrated. However, using purified TS it was demonstrated that dFdUMP and not dFdCMP competitively inhibited TS with a Ki of 130 μM, without ternary complex formation. In conclusion, in this paper we reveal a new target of dFdC: thymidylate synthase.     

RNA double-helical fragments at atomic resolution: II. The crystal structure of sodium guanylyl-3′,5′-cytidine nonahydrate

The crystal structure of sodium guanylyl-3′,5′-cytidine (GpC) nonahydrate has been determined by X-ray diffraction procedures and refined to an R value of 0.054. GpC crystallizes with four molecules per monoclinic unit cell, space group C2, with cell dimensions: $\text{a = 21.460, b = 16.297, c = 9.332}\text{A}\text{?}\text{and}\text{β = 90.54 °}$. Two molecules of GpC related by the 2-fold axis of the crystal form a small segment of right-handed, anti-parallel double-helical RNA in the crystal. Guanine is paired to cytosine through three hydrogen bonds of lengths 2.91, 2.95 and 2.86 Å. The bases along each strand are heavily stacked at a distance of about 3.4 Å. The fragments form skewed flattened rods within the lattice by the inter-molecular stacking of guanines with each other and the stacking of cytosine with the guanosine Ol′atom. The sodium cations are bound only to the ionized phosphate groups in this structure and exhibit face-sharing octahedral co-ordination. The sodium cations serve to bridge the rods of GpC fragments and organize them into sheets within the crystal. There are 18 water molecules per double-helical fragment which are all part of the first co-ordination shell of nitrogen, oxygen or sodium atoms.     

Ordered transcription of RNA tumor virus genomes.

The crystal structure of sodium adenylyl-3′,5′-uridine (ApU) hexahydrate has been determined by X-ray diffraction procedures and refined to an R factor of 0.057. ApU crystallizes with two molecules per asymmetric unit in a monoclinic unit cell, space group P2₁, with cell dimensions: $\text{a = 18.025, b = 17.501, c = 9.677}\text{A}\text{?}\text{and}\text{β = 99.45 °}$. The two independent molecules of ApU form a small segment of right-handed antiparallel double-helical RNA in the crystal, with Watson-Crick base-pairing between adenine and uracil. This is the first time that this Watson-Crick base-pair has been seen unambiguously at atomic resolution and it is also the first time that a nucleic acid fragment with double-helical symmetry has been seen at atomic resolution. The distance between the C1′ atoma of the adenine-uracil base-pair is slightly shorter than the analogous distance seen in guanine-cytosine base-pairs. The bases in each strand are heavily stacked. One sodium cation binds to the phosphates, as expected; however, the other sodium cation binds on the dyad axis in the minor groove of the double helix. It is co-ordinated directly to the two uracil carbonyl groups which protrude into the minor groove and is shielded from the nearest phosphates by a shell of water. This binding appears to be sequence-specific for ApU. One of the adenines also forms a pair of hydrogen bonds to a nearby ribose, utilizing N6 and N7. The 12 water molecules per double-helical fragment are all part of the first co-ordination shell. The ions and the symmetry of the double-helical fragment are the major organizing elements of the solvent region.     

Two methylated flavones from Artemisia frigida

Two new highly oxygenated flavones were isolated from Artemisia frigida. Their structures were determined by spectroscopic methods as 5,7,4′-trihydroxy-6,3′,5′-trimethoxyflavone and 5,7,3′-trihydroxy-6,4′,5′-trimethoxyflavone.