Characterization of adducts formed in the reaction of glutaraldehyde with 2'-deoxyadenosine

Glutaraldehyde (1,5-pentanedial) is a widely used industrial chemical that has been found to be mutagenic in bacteria and mammalian cells. In this study, we examined the reaction of glutaraldehyde with 2'-deoxyadenosine and calf thymus DNA in aqueous buffered solutions. The 2'-deoxyadenosine adducts were isolated by reversed phase HPLC and characterized by their UV absorbance and 1H and 13C NMR spectroscopic and mass spectrometric features. The reaction produced three major adducts. The adduct dA567 was derived from two 2'-deoxyadenosine units bound together with a piperidine unit, and its yield was 10.4%. The carbons of the piperidine ring originated from glutaraldehyde, whereas the nitrogen of the ring originated from the exocyclic amino group of one of the 2'-deoxyadenosine units. The adduct dA451d (yield 0.6%) was similar in structure to dA567, but one of the deoxyribose moieties from 2'-deoxyadenosine was missing. The third adduct, dA334, consisted of a hydroxy-tetrahydropyridine moiety derived from glutaraldehyde and N6 of 2'-deoxyadenosine (yield 4.0%). Furthermore, LC-ESI-MS/MS analysis of the reaction mixture revealed the formation of compounds with ion peaks of m/z = 352. None of these compounds were sufficiently stable for preparative isolation. They were tentatively identified as a pair of diastereomers of 2,6-dihydroxypiperidine derivatives, which are likely precursors to dA334. Plausible mechanisms for the formation of the adducts are presented. In the reaction of glutaraldehyde with single and double stranded calf thymus DNA, the dA334 adduct was formed.     

Investigation of the adducts formed by reaction of malondialdehyde with adenosine

Malondialdehyde (MDA) forms oligomeric adducts with DNA bases. It has been proposed that the 2:1 MDA-guanosine (M2G) and 3:1 MDA-adenosine (M3A) adducts result from sequential addition of MDA molecules to the nucleoside base. Reaction of 1:1 MDA-guanosine (M1G) and 1:1 MDA-adenosine (M1A) adducts with MDA does not produce the multimeric adducts. This suggests they arise by reaction of the nucleoside bases with oligomers of MDA. If so, the proposed structure for M3A is inconsistent with the addition of an MDA trimer to adenosine. Therefore, we investigated the structure of this molecule. Two-dimensional double quantum filtered COSY and hetero-COSY NMR experiments were performed, and a series of insensitive nuclei assignment by polarization transfer (INAPT) NMR spectra were also recorded. The results of these experiments revealed the presence of a propano group and two alpha,beta-unsaturated aldehydes. The UV spectrum of M3A displayed a maximum at 326 nm, similar to that of N6-[3-oxo-1(E)-propenyl]adenosine (M1A). The adducts were reduced with sodium borohydride for comparison of the UV and NMR spectra. On the basis of our results, a new structure for M3A is proposed which is tentatively named 6(5*,7*-diformyl-2*H-3*,6*-dihydro-2*,6*-methano-1*,3*-oxazocin -3*-yl)-9-beta-D-ribofuranosylpurine.     

Characterization of adducts formed in the reaction of 2-chloro-4-methylthiobutanoic acid with 2'-deoxyguanosine

2-chloro-4-methylthiobutanoic acid (CMBA) is a direct-acting mutagen found in salt-nitrite-treated Sanma fish or similarly treated methionine solution. In this study, CMBA was reacted with 2'-deoxyguanosine (dG) in phosphate buffer (pH 7.4) at 37 degrees C. The HPLC-UV analysis showed that two products were mainly formed during the reaction. These were isolated, purified by semipreparative HPLC, and characterized as N7-guanine adducts: N7-(3-carboxy-3-methylthiopropyl)guanine (A1) and N7-(1-carboxy-3-methylthiopropyl)guanine (A2). Furthermore, liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) analysis was employed to investigate the possible formation of minor products during the time-course of the reaction of CMBA with dG. It was found that N7-dG adducts, the precursors of A1 and A2, were formed early in the reaction and that subsequently the spontaneous depurination occurred to yield stable N7-guanine adducts A1 and A2. Stability studies in phosphate buffer (pH 7.4) at 37 degrees C showed that the amount of each N7-dG adduct decreased rapidly with a half-life of 6 h and 4 h to yield A1/A2, respectively. A regioisomer of N7-dG adducts was also observed in the LC/ESI-MS/MS analysis, but it was not characterized in detail because it was present only in trace amounts. On the basis of structural features, A1 and A2 seemed to be formed from the reaction of dG with 1-methyl-2-thietaniumcarboxylic acid, an intermediate resulting from the cyclization of CMBA. However, A2 might also have formed from the direct reaction of dG and CMBA. N7-Alkylation of the guanine residue and subsequent depurination are known to produce apurinic sites in DNA that induce point mutations and may be responsible for the observed CMBA-induced mutagenesis.     

Synthetic studies of the bioactive natural products by using the thermal electrocyclic reaction of 6 pi electron systems

We are developing the synthesis of biologically interesting condensed-heteroaromatic compounds, including natural products by the thermal electrocyclic reaction of 6 pi electron system incorporating the double bond of the principal aromatic or heteroaromatic ring. In this report, we describe three types of electrocyclic reactions as follows; 1) the synthesis of highly-substituted carbazole alkaloids based on the allene-mediated electrocyclic reaction involving an indole 2,3-bond, 2) the synthesis of beta-carboline alkaloids and isoquinoline-5,8-quinone alkaloids based on the thermal electrocyclic reaction of an 1-azahexatriene system involving an indole 2,3-bond or benzene 1,2-bond, and 3) the synthesis of new tetracyclic pyrido[2,3-b]indole, grossularines, based on the thermal electrocyclic of an 2-azahexatriene system including the indole 2,3-bond.     

治疗老年性痴呆病的天然药物成分

随着人类社会年龄结构趋向老龄化 ,老年性痴呆症发病率日趋上升。寻找治疗老年痴呆症的有效药物已经成为刻不容缓的问题。近年来国内外学者在应用天然药物有效成分治疗老年性痴呆症做了大量的工作 ,有望从中开发出治病治疗老年性痴呆的新药     

Characterization of 1,2,3,4-diepoxybutane-2'-deoxyguanosine cross-linking products formed at physiological and nonphysiological conditions

1,2,3,4-Diepoxybutane (DEB), an in vivo metabolite of 1,3-butadiene (BD), is a carcinogen and mutagen. The strong carcinogenicity/mutagenicity of DEB has been attributed to its high DNA reactivity and cross-linking ability. Recently, we have demonstrated that under in vitro physiological conditions (pH 7.4, 37 degrees C), the reaction of DEB with 2'-deoxyguanosine (dG) produced two diastereomeric pairs of the major nucleoside adducts resulting from alkylation at the N1- and N7-positions of dG, that is, 2'-deoxy-1-(2-hydroxy-2-oxiranylethyl)guanosine and 2'-deoxy-7-(2-hydroxy-2-oxiranylethyl)guanosine, respectively [Zhang, X.-Y., and Elfarra, A. A. (2005) Chem. Res. Toxicol. 18, 1316]. As each of these adducts contains an oxirane ring, the abilities of these adducts to form cross-linking products with dG under physiological conditions were investigated. Incubation of the N7 nucleoside adducts and their corresponding guanine product with dG led to formation of 7,7'-(2,3-dihydroxy-1,4-butanediyl)bis[2-amino-1,7-dihydro-6H-purin-6-one] (bis-N7G-BD), a known DEB cross-linking product. Incubation of the N1 nucleoside adducts with dG led to formation of a pair of diastereomers of 2'-deoxy-1-[4-(2-amino-1,7-dihydro-6H-purin-6-on-7-yl)-2,3-dihydroxybutyl]-guanosine (N7G-N1dG-BD), which are novel cross-linking products. Interestingly, the reaction of DEB with dG in glacial acetic acid at 60 degrees C yielded different cross-linking products, which were characterized as 2-amino-9-hydroxymethyl-4-{4-[2-amino-9- or 7-(4-acetyloxy-2,3-dihydroxybutyl)-1,7-dihydro-6H-purin-6-on-7- or 9-yl]-2,3-dihydroxybutyl}-8,9-dihydro-7H-[1,4]oxazepino[4,3,2-gh]purin-8-ol (PA2) and 9,9'-bis(4-acetyloxy-2,3-dihydroxybutyl)-7,7'-(2,3-dihydroxy-1,4-butanediyl)bis[2-amino-1,7-dihydro-6H-purin-6-one] (PA4). Collectively, these results increase our understanding of the chemical reactivity and cross-linking ability of DEB under both physiological and nonphysiological conditions.     

黏球菌产生的活性天然产物

从化学结构、生物学活性、生物合成、应用开发等角度,综述了已有文献报道的黏球菌活性天然产物,重点介绍了作用于肌动蛋白的大环内酯类化合物rhizopodin、作用于呼吸链的肽类化合物myxothiazol和多烯类化合物myxalamid、作用于核酸的芳香类化合物myxopyronin和saframycin Mx1,以及作用于细胞壁的大环类化合物myxovirescin,阐明了黏球菌次级代谢产物的化学结构多样性和生物活性多样性,为进一步开发黏球菌活性天然产物提供线索。     

Modulation of k-Ras signaling by natural products

Ras proteins regulate diverse cellular pathways that are important in the growth and spread of malignancies, including cell proliferation, cell cycle regulation, cell survival, angiogenesis and cell migration. These proteins lack the conventional transmembrane or hydrophobic domain typical of membrane associated proteins. Being small and hydrophilic in nature, these proteins undergo four-stage post-translational lipid modifications viz. prenylation, AAX proteolysis, carboxymethylation and palmitoylation for membrane localization which is important for their function. Therefore, enzymes involved in these modifications viz. farnesyl transferase (FTase), geranylgeranyl transferase-I (GGTase-I), geranylgeranyl transferase-II (GGTase-II), Ras converting enzyme-1 (Rce-1) and isoprenyl cysteine methyl transferase (ICMT) are emerging as potential therapeutic targets for the discovery of newer anticancer therapeutics. Several natural products have shown modulation of these post-translational enzymes. In the present review, natural products isolated from terrestrial as well as marine sources showing ability to modulate these k-Ras post-translational targets and their promise as potential anticancer agents have been discussed. A total of 157 natural products with 141 corresponding references have been covered.     

肠道细菌对天然药物代谢的研究进展Ⅰ

目的：介绍肠道细菌对天然药物代谢的最新研究进展。方法：综述近年来国内外相关文献,对黄酮、皂甙、木脂素、环烯醚萜苷类等天然产物在肠道细菌作用下的代谢情况进行总结归纳。结果：天然产物经肠道细菌代谢后,转化为具有病理或毒理活性的新化合物。结论：许多天然药物以前药形式存在,肠道细菌在其代谢中发挥着至关重要的作用。     

Modulating TNF-alpha signaling with natural products

Natural products have been, and continue to be, a major source of pharmacologically active substances from which drugs can be developed. Currently, tumor necrosis factor-alpha (TNF-alpha) inhibitors from natural origins are being advanced for the treatment of inflammatory disorders. Elevated TNF-alpha synthesis has been associated with the development of diabetes, septic shock, tumorigenesis, rheumatoid arthritis, psoriatic arthritis and inflammatory bowel disease. Currently, only protein-based drugs are available for the clinical inhibition of TNF-alpha activity. Small-molecule drugs that can regulate TNF-alpha levels or activity might provide a cost-effective alternative to protein-based therapeutics. This review briefly highlights the physiological and pathological roles of TNF-alpha, and covers those natural compounds capable of interfering with TNF-alpha activity.     

与微管作用的抗肿瘤天然产物的研究进展

自从紫杉醇广泛应用于临床治疗以来,与微管作用的抗肿瘤天然产物的发现、化学修饰和机制研究已经成为学术和临床研究的热点。介绍了与微管作用的抗肿瘤天然产物的研究情况,包括紫杉醇、埃博霉素、disco-dermolid、考布他汀、软海绵素、海兔毒素、那可丁等,简要探讨了目前存在的问题和未来的发展方向。     

Fluorinated natural products with clinical significance

The modification of natural products in an effort to alter their biochemical capacity is a common technique utilized by synthetic and medicinal chemists. Fluorine substitution imparts unique and advantageous physiochemical properties that can be shrewdly employed to constructively alter pharmacological agents. The adornment of natural products with fluorine has proven beneficial in several examples. This overview discusses several of the most relevant fluorinated natural products under current examination.     

Identification of products formed by reaction of 3',5'-di-O-acetyl-2'-deoxyguanosine with hypochlorous acid or a myeloperoxidase-H2O2-Cl- system

Hypochlorous acid (HOCl), generated by myeloperoxidase from H(2)O(2) and Cl(-), plays an important role in host defense and inflammatory tissue injury. We have studied the reaction of 3',5'-di-O-acetyl-2'-deoxyguanosine with reagent HOCl and with a human myeloperoxidase-H(2)O(2)-Cl(-) system in order to characterize polar reaction products. When 100 microM 3',5'-di-O-acetyl-2'-deoxyguanosine was reacted with 100 microM HOCl at pH 7.4 and 37 degrees C and the reaction was terminated by N-acetylcysteine, 3',5'-di-O-acetyl derivatives of previously reported products, such as diastereomers of spiroiminodihydantoin nucleoside, a diimino-imidazole nucleoside, an amino-imidazolone nucleoside, and 8-chloro-2'-deoxyguanosine were formed. In addition, we report the formation of 3',5'-di-O-acetyl derivatives of a guanidinohydantoin nucleoside, an iminoallantoin nucleoside, and a diamino-oxazolone nucleoside in this system. The identification of the products was based on their identical ESI-MS and UV spectra and HPLC retention times with authentic compounds synthesized with other oxidation systems. All of these products were also formed in the reaction of 3',5'-di-O-acetyl-2'-deoxyguanosine with the myeloperoxidase-H(2)O(2)-Cl(-) system under mildly acidic conditions. The yields of the products were greatly affected by the pH of the reaction mixture. The total yields of these products formed by HOCl at pH 7.4 and by the myeloperoxidase-H(2)O(2)-Cl(-) system at pH 4.5 were 72 and 43% of the consumed 3',5'-di-O-acetyl-2'-deoxyguanosine, respectively, indicating that nearly half of the consumption of 3',5'-di-O-acetyl-2'-deoxyguanosine by HOCl and the myeloperoxidase-H(2)O(2)-Cl(-) system can be accounted for by the formation of these products.     

Cancer chemotherapy with novel bioactive natural products

Cancer is the primary cause of death on a global scale. Every year, 8.8 million people die because lung, prostate gland, colorectal, and hepatic cancers are more common in men. In contrast, mammary glands, large intestine, bronchi, cervix, and abdomen cancers are more common in women. The Food and Drug Administration of the United States of America has approved plant-based medications for cancer treatment. Examples include taxanes, such as paclitaxel, and vinca alkaloids, such as vincristine and...     

Targeting cancer stem cells with natural products

The cancer stem cell (CSC) hypothesis presents a fundamentally different paradigm for cancer treatment. CSCs reflect a small fraction of tumor initiating cells capable of sustained self-renewal and differentiation to form the heterogeneous tumor bulk. In order to cure cancer, it is necessary to eliminate cancer stem cells in addition to differentiated cancer cells to decrease metastasis, reduce recurrence, and improve patient survival. In this article, we review cancer stem cell signaling pathways, including Wnt, Hedgehog, and Notch, as well as interactions of CSCs with the tumor microenvironment. We also review methods to isolate CSCs and demonstrate therapeutic efficacy of natural products to modulate these signaling pathways for eliminating CSCs.     

Synthesis of marine natural products with antimalarial activity

The role played by synthetic organic chemistry of marine metabolites as potential leads for drug discovery of antimalarial agents is discussed. Syntheses of the most promising molecules are summarized, with emphasis on structure-activity relationship (SAR) studies and their mechanism of action.     

N-Nitroso products from the reaction of indoles with Angeli's salt

While nitroxyl (HNO) has been shown to engage in oxidation and hydroxylation reactions, little is known about its nitrosating potential. We therefore sought to investigate the kinetics of formation and identity of the reaction products of the classical nitroxyl donor Angeli's salt (AS) with three representative tryptophan derivates (melatonin, indol-3-acetic acid, and N-acetyl-l-tryptophan) in vitro. In the presence of oxygen and at physiological pH, we find that the major products generated are the corresponding N-nitrosoindoles with negligible formation of oxidation and nitration products. A direct comparison of the effects of AS, nitrite, peroxynitrite, aqueous NO* solution, and the NO-donor DEA/NO toward melatonin revealed that nitrite does not participate in the reaction and that peroxynitrite is not an intermediate. Rather, N-nitrosoindole formation appears to proceed via a mechanism that involves electrophilic attack of HNO on the indole nitrogen, followed by a reaction of the intermediary hydroxylamine derivative with oxygen. Further in vivo experiments demonstrated that AS exhibits a unique nitrosation signature which differs from that of DEA/NO inasmuch as substantial amounts of a mercury-resistant nitroso species are generated in the heart, whereas S-nitrosothiols are the major reaction products in plasma. These data are consistent with the notion that the generation of nitroxyl in vivo gives rise to formation of nitrosative post-translational protein modifications in the form of either S- or N-nitroso products, depending on the redox environment. It is intriguing to speculate that the particular efficiency of nitroxyl to form N-nitroso species in the heart may account for the positive inotropic effects observed with AS earlier.