Poly-cis carotene pathway in the Scenedesmus mutant C-6D

The mutation of Scenedesmus obliquus strain C-6D is expressed in the dark only. Under these conditions, this strain synthesizes acyclic poly-cis carotenes. Cyclic carotenoids like -carotene or xanthophylls are absent. In the light the normal cyclic carotenes and xanthophylls are synthesized in the all-trans configuration. The poly-cis carotencs present in dark cultures have been analysed and quantitated. It could be shown that these poly-cis carotenes are identical with the poly-cis carotenes synthesized by the tomato mutant Lycopersicon esculentum var. Tangella. The poly-cis pathways, however, are different regulated in the two organisms. The tomato mutant accumulates prolycopene as the major carotene, whereas the mutant C-6D accumulates mainly pro--carotene. Furthermore, the mutation in Tangella is constitutive in light in contrast to Scenedesmus C-6D. Besides that, Scenedesmus C-6D synthesizes a further cis-carotene isomer of phytofluene as well as of -carotene. The configuration of these carotenes still have to be elucidated. The occurrence of this poly-cis carotene biosynthetic pathway by a mutation of only one enzyme, the phytoene desaturase which, however, is only expressed in darkness under heterotrophic conditions, is discussed.     

Incomplete cerebral ischemia in the rat provokes increase of tissue and plasma malondialdehyde

Short-term incomplete cerebral ischemia was induced in the rat by bilaterally clamping for 5 min the common carotid arteries; subsequent reperfusion of 10 min was obtained by removing carotid occlusion. At the end of ischemia or reperfusion, animals were sacrificed by decapitation. A control group was represented by sham-operated rats. Peripheral venous blood samples were withdrawn from the femoral vein from rats subjected to cerebral reperfusion 5 min before ischemia, at the end of ischemia, and 10 min after reperfusion. A highly sensitive HPLC method for the direct determination of malondialdehyde, oxypurines, and nucleosides was used on 200 μL of brain tissue and plasma extracts. Incomplete cerebral ischemia induced the, appearance of a significant amout of tissue malondialdehyde (undetectable in control animals) and a decrease of ascorbic acid. A further 6.6-fold increase of malondialdehyde and a 18.5% decrease of ascorbic acid occurred after 10 min of reperfusion. Plasma malondialdehyde, which was present in minimal amount before ischemia, significantly increased after 5 min of ischemia, being strikingly augmented after 10 min of reperfusion. A similar trend was observed for oxypurines and nucleosides. From these data, it can be affirmed that tissue concentrations of malondialdehyde and ascorbic acid, and plasma levels of malondialdehyde, oxypurines, and nucleosides, reflect both the oxygen radical-mediated tissue injury and the depression of energy metabolism thus representing early biochemical markers of short-term incomplete brain ischemia, and reperfusion in the rat.     

Fast atom bombardment combined with tandem mass spectrometry for the determination of nucleosides

The positive and negative ion fast atom bombardment (FAB) mass spectra and fast atom bombardment collisionally activated decomposition (CAD) spectra of a series of nucleosides and two dinucleotides are reported. The nucleosides studied are substituted forms of guanosine, adenosine, nebularine, tubercidin, uridine, and related pyrimidines. The FAB and CAD data both contain similar information. The CAD spectra are found to provide some structural information not found in the FAB mass spectra. Tandem mass spectrometry also allows emphasis to be put on weak fragments which are either not observed in the FAB mass spectrum or are lost in the matrix ion signals.     

Template-directed reactions of aminonucleosides

Summary We have studied the reactions between adenosine 5-phosphorimidazolide and 9-(2-amino-2-deoxyxylofuranosyl) adenine (I) or 3-methylamino-3-deoxyadenosine (II), both with and without a poly (U) template. We find that both amino compounds react much more rapidly than does adenosine, in the absence of a template. The rate of reaction is greatly enhanced by a poly (U) template in the case of I, but the enhancement is slight in the case of II.Abbreviations A adenosine - xylo A_NH2 9-(2-amino-2-deoxy--D-xylofuranosyl) adenine - A_NHMe 3-methylamino-3-deoxyadenosine - ImpA adenosine 5-phosphorimidazolide - A³ pA adenylyl-[35]-adenosine - A² pA adenylyl-[25]-adenosine - U_NPA adenylyl-[52]-2-amino-2-deoxyuridine - xylo A_NPA 9-[adenylyl-(52)-2-amino-2-deoxy--D-xylofuranosyl]adenine - A_(NMe)pA adenylyl-[53]-3-methylamino-3-deoxyadenosine - pA adenosine 5phosphate - AppA P₁, P₂-diadenosine 5pyrophosphate - (pA)_n n = 2, 3 [2-5]-linked oligomers of pA - A² pA² pA [2-5]-linked trinucleoside diphosphate of A - poly (U) polyuridylic acid     

5-alkylvinyl-1,2,4-triazole nucleosides: Synthesis and biological evaluation

Abstract

Some 5-substituted ribavirin analogues have a high antiviral and anticancer activity, but their mechanisms of action are obviously not the same as their parent compound. The SAR studies performed on 3 (5)-substituted 1,2,4-triazole nucleosides have shown a high dependency between the structure of the 3 (5)-substituent and the level of antiviral/anticancer activity. The most active substances of the row contain coplanar with the 1,2,4-triazole ring aromatic substituent which is connected by a rigid ethynyl bond. However, the compounds with the trans-vinyl linker also had antiviral activity. We decided to study the antitumor activity of ribavirin analogues with alkyl/aryl vinyl substituents in the 5th position of the 1,2,4-triazole ring. Protected nucleoside analogues with various 5-alkylvinyl substituents were obtained by Horner-Wadsworth-Emmons reaction from the common precursor and converted to the nucleosides. Arylvinyl nucleosides were synthesised according the reported procedures. All compounds did not show significant antiproliferative activity on several tumour cell lines. Coplanar aromatic motif in the 5-substituent for the anticancer activity manifestation was confirmed.     

Highly Efficient and Facile Synthesis of 5-Azido-2′-Deoxyuridine

Previously reported syntheses of the photoaffinity label 5-azido-2′-deoxyuridine are rather inefficient and involve the tedious preparation of a 5-nitro intermediate. To overcome these inconveniences, we have developed a new approach from the commercially available 5-bromo-2′-deoxyuridine nucleoside. Our synthetic route makes use of a benzylamination reduction sequence. Using this strategy, the 5-azido-2′-deoxyuridine photolabel is prepared in three steps and quantitative yields.     

Synthesis of D‐Altritol Nucleosides with a 3′‐O‐Tert‐Butyldimethylsilyl Protecting Group

Four D‐altritol nucleosides with a 3′‐O‐tert‐butyldimethylsilyl protecting group are synthesized (base moieties are adenine, guanine, thymine and 5‐methylcytosine). The nucleosides are obtained by ring opening reaction of 1,5:2,3‐dianhydro‐4,6‐O‐benzylidene‐D‐allitol. Optimal reaction circumstances (NaH, LiH, DBU, phase transfer, microwave irridation) for the introduction of the heterocycles are base‐specific. For the introduction of the 3′‐O‐silyl protecting group, long reaction times and several equivalents of tert‐butyldimethylsilyl chloride are needed.     

Chemo-enzymatic Synthesis of 3-Deoxy-β-D-ribofuranosyl Purines and Study of Their Biological Properties

Abstract

9-(3-Deoxy-β-d-erythro-pentofuranosyl)-2,6-diaminopurine (2) was synthesized by an enzymatic transglycosylation of 2,6-diaminopurine using 3′-deoxycytidine (1) as a donor of the sugar moiety. Nucleoside 2 was transformed to 3′-deoxy guanosine (3), 9-(3-deoxy-β-d-erythro-pentofuranosyl)-2-amino-6-oxopurine (3′-deoxyisoguanosine; 4), and 9-(3-deoxy-β-d-erythro-pentofuranosyl)-2-fluoroadenine (5). Compounds 2–5 were evaluated for their anti-HIV activity.     

Synthesis of Cyclobutane Nucleosides

2-(6-Chloropurinyl)-3-benzoyloxymethylcyclobutanone can be prepared by reaction of 6-chloropurine with 3-benzoyloxymethyl-2-bromocyclobutanone. The N-alkylation gave both N-9 and N-7 regioisomers. Both regioisomers upon hydride reduction followed by aminolysis gave the corresponding adenine nucleoside analogues. However, the N-7 series led to the hypoxanthine analogues as byproducts.     

Synthesis of (−)‐DAPD

A new synthesis of (?)‐DAPD, suitable for large scale development, is described.