Stereospecific syntheses of 3'-deuterated pyrimidine nucleosides and their site-specific incorporation into DNA

[reaction: see text] 2'-Deoxy-3'-deutero pyrimidines have been synthesized in high yields and incorporated into deoxyoligonucleotides using standard phosphoramidite chemistry. A key synthetic step is a stereospecific reduction of 3'-keto nucleosides using sodium triacetoxyborodeuteride to give 3'-deuterated thymidine and 2'-deoxy uridine nucleosides. Conversion of the corresponding phorphoramidites 7a and 7b to 4-triazolo derivatives has, for the first time, enabled incorporation of 2'-deoxy-3'-deutero cytidine and 2'-deoxy-3'-deutero-5-methyl cytidine into oligonucleotides.     

Synthesis of novel exocyclic amino nucleosides by parallel solid-phase combinatorial strategy

A versatile parallel solid-phase combinatorial strategy was developed for the synthesis of large nucleoside libraries. Twelve libraries L1-12 of 1152 novel exocyclic triazinylamino nucleosides and one library L13 of 82 new substituted clitocine derivatives were synthesized in high quality as natural product mimic nucleosides on the semi-automated synthesizer. The polystyrene MMT-Cl resin was selected and utilized. The key intermediate resins 5 and 9 loaded with the corresponding scaffolds were prepared and validated with various amines before parallel synthesis. After a variety of amino building blocks were validated, 56 primary amines in 12 groups (building block set A) and 24 secondary amines in 3 groups (building block set B) were selected and utilized to combinatorialize the first and the second reactive sites on scaffold 5 for the synthesis of libraries L1-12. Eighty-two amines (building block set C) were utilized for the synthesis of clitocine library L13. Thirteen libraries of 1234 novel exocyclic amino nucleosides were all analyzed and characterized by high throughput LC-MS. 81.3-100% of the library members in 13 libraries show more than 60% purity, and 65.7-92.7% of the library members in these libraries show 80-100% purity. The strategy can be widely used for the synthesis of other diverse nucleoside libraries.     

Novel bicyclic nucleoside analogue (1S,5S,6S)-6- hydroxy-5-hydroxymethyl-1-(uracil-1-yl)-3,8-dioxabicyclo[3.2.1]octane: synthesis and incorporation into oligodeoxynucleotides

The novel bicyclic nucleoside (1S,5S,6S)-6-hydroxy-5-hydroxymethyl-1-(uracil-1-yl)-3,8-dioxabicyclo[3.2.1]octane [2'-deoxy-1'-C,4'-C-(2-oxapropano)uridine] (15), expected to be restricted into an O4'-endo furanose conformation, was synthesized from the known 1-(3'-deoxy-beta-D-psicofuranosyl)uracil 5. The phosphoramidite derivative of 15 was successfully incorporated into oligodeoxynucleotides using standard methods, and thermal denaturation studies showed moderate decreases in duplex stabilities of -2.1 and -1.5 degrees C per modification toward complementary DNA and RNA, respectively.     

New scaffolds for combinatorial synthesis. 1. 5-sulfamoylisatins and their reactions with 1,2-diamines

3,3-Dichloro-5-(4-methylpiperidinosulfonyl)-2-indolinone (3) and 5-sulfamoylisatins 4 have been synthesized from 5-chlorosulfonyl-3,3-dichloro-2-indolinone (1). Compounds 4 are promising scaffolds for the solid- and liquid-phase syntheses of new combinatorial libraries of various heterocycles. Thus, the reactions of 4 with 1,2-diamines, such as o-phenylenediamine (5) and aminoguanidine hydrochloride (6), 1,2-diaminoimidazoles (9), and thiosemicarbazide led, respectively, to new heterocycles 7 and 8 and new combinatorial libraries of triazinoindoles 10 and 15. Chemsets 4, 10, and 15 were isolated as crystalline solids that were purified by recrystallization from a suitable solvent and characterized by spectroscopic methods.     

Synthesis of pyrimidine 2'-deoxy ribonucleosides branched at the 2'-position via radical atom-transfer cyclization reaction with a vinylsilyl group as a radical-acceptor tether

Recently, we developed a regio- and stereoselective method for introducing a vinyl group at the position beta to a hydroxyl group in halohydrins or alpha-phenylselenoalkanols via a radical atom-transfer cyclization reaction with a vinylsilyl group as a temporary connecting radical-acceptor tether. The synthesis of 2'-deoxy-2'-C-vinyl- and 2'-deoxy-2'-C-hydroxymethyluridines (7 and 8, respectively) and the corresponding 2'-deoxycytidine congeners (10 and 11, respectively), which were designed as potential antitumor and/or antiviral agents, was achieved using this radical atom-transfer cyclization as the key step. When the 2'-deoxy-2'-iodo-5'-O-monomethoxytrityl (MMTr) uridine derivative 19a, bearing a vinylsilyl group at the 3'-hydroxyl group, was heated with (Me(3)Sn)(2) and AIBN in benzene, the corresponding radical atom-transfer product was generated, which in turn was successively treated with tetrabutylammonium fluoride and TBSCl/imidazole to give the desired 2'-deoxy-5'-O-MMTr-3'-O-TBS-2'-C-vinyluridine (25). Compound 25 was successfully converted into the target 2'-deoxy-2'-branched pyrimidine ribonucleosides 7, 8, 10, and 11.     

Adsorption characteristics of as(III) and as(V) with titanium dioxide loaded Amberlite XAD-7 resin.

The adsorption characteristics of As(V) and As(III) on titanium dioxide loaded Amberlite XAD-7 resin have been studied. The resin was prepared by impregnation of Ti(OC2H5)4 followed by hydrolysis with ammonium hydroxide. Batch adsorption experiments were carried out as a function of the pH, shaking time and the concentration of As(V) and As(III) ions. The resin showed a strong adsorption for As(V) from pH 1 to 5 and for As(III) from pH 5 to 10. The adsorption isotherm data for As(V) at pH 4 fitted well to a Langmuir equation with a binding constant of 59 dm3 mol(-1) and a capacity constant of 0.063 mmol g(-1). The data for As(III) at pH 7 also fitted well to a Langmuir equation with a binding constant of 5.4 dm3 mol(-1) and a capacity constant of 0.13 mmol g(-1). The effect of diverse ions on the adsorption of arsenic was also studied. Column adsorption experiments showed that the adsorption of As(III) is more favorable compared to As(V), due to both the faster adsorption and larger capacity for As(III) than As(V).     

Synthesis of 2'-C-alpha-(hydroxyalkyl) and 2'-C-alpha-alkylcytidine phosphoramidites: analogues for probing solvent interactions with RNA

Nucleoside analogues bearing 2'-C-alpha-(hydroxyalkyl) and 2'-C-alpha-alkyl substitutes have numerous applications in RNA chemistry and biology. In particular, they provide a strategy to probe the interaction between the 2'-hydroxyl group of RNA and water. To incorporate these nucleoside analogues into oligonucleotides for studies of the group II intron (Gordon, P. M.; Fong, R.; Deb, S.; Li, N.-S.; Schwans, J. P.; Ye, J.-D.; Piccirilli, J. A. Chem. Biol. 2004, 11, 237), we synthesized six new phosphoramidite derivatives of 2'-deoxy-2'-C-alpha-(hydroxyalkyl)cytidine (36: R = -(CH2)2OH; 38: R = -(CH2)3OH; 40: R = -(CH2)4OH) and 2'-deoxy-2'-C-alpha-alkylcytidine (37: R = -CH2CH3; 39: R = -(CH2)2CH3; 41: R = -(CH2)3CH3) from cytidine or uridine via 2'-C-alpha-allylation, followed by alkene and alcohol transformations. Phosphoramidites 36 and 37 were prepared from cytidine in overall yields of 14% (10 steps) and 7% (11 steps), respectively. Phosphoramidites 38 and 39 were prepared from uridine in overall yields of 30% (10 steps) and 13% (11 steps), respectively. Phosphoramidites 40 and 41 were synthesized from uridine in overall yields of 21% (13 steps) and 25% (14 steps), respectively.     

Synthesis of Rhenium‐Centric Reverse Turn Mimics

Molecular scaffolds have been shown to facilitate and stabilise secondary structural turn elements, with a central core‐arranging functionality in a defined three‐dimensional orientation. In a peptide‐based molecular imaging probe, this approach is of particular value as it would essentially “hide” a metal radioisotope within the ligand framework, making the labelling element a critical component of the receptor‐bound structure. Starting from a 1,2‐diaminoethane loaded 2‐chlorotrityl resin, a versatile set of triamine ligand systems were synthesised by using solid‐phase Fmoc‐based peptide chemistry. The resultant resin‐bound peptides then underwent amide reduction by treatment with borane‐THF at 65 °C. This provided complete conversion to the corresponding polyamine entities in high purity for the majority of the amino acids utilised. The triamines were then coordinated on solid support by using [NEt₄]₂[Re(CO)₃(Br)₃] followed by resin cleavage and HPLC purification, to give the desired rhenium coordinated species. We have shown that amino acid sequences can be assembled, reduced and coordinated on‐resin, resulting in a versatile set of metal–ligand constructs. These studies could be expanded to generate libraries of turn‐based peptidomimetics containing Re/Tc^I organometallic scaffolds, with the intention of developing an improved approach for finding new diagnostic and therapeutic radiopharmaceutical entities.     

Synthesis and mass spectrometry studies of branched oxime ether libraries. Mapping the substitution motif via linker stability and fragmentation pattern.

The oxime ether chemistry has recently been used as a convenient approach to preparing potentially highly diverse combinatorial libraries. The synthetically easiest way to form the libraries is convergent, i.e., via reaction of a branched scaffold containing two or more aminooxy linker groups, with a variety of carbonyl substituents. We show here that such reactions between aldehydes and ketones of different structure with the scaffolds containing different types of aminooxy groups can lead to the formation of virtually all expected components in the model mixtures 1-3 formed from three scaffolds (7-9) and eight substituents (R(1)-R(8)). One important problem with the branched libraries is that the libraries formed from the more complex scaffolds, such as 11, contain multiple regioisomers. The results of extensive analysis of a variety of library components by mass spectrometry presented here show that the differences in the MS-MS fragmentation energies for different linkers yield regiochemical information essential for identification of individual library components.     

Lithiation at the 6-position of uridine with lithium hexamethyldisilazide: crucial role of temporary silylation

Lithium hexamethyldisilazide (LiHMDS) can mediate silylation at the 6-position of uridine, although LiHMDS alone is not able to generate the C-6-lithiated uridine. Experimental results showed that temporary silylation of O-4 (or N-3) of the uracil ring triggers the C-6 lithiation with LiHMDS. This finding allowed us to develop an efficient intramolecular alkylation of 5'-deoxy-5'-iodouridine to furnish 6,5'-C-cyclouridine. [reaction--see text]     

从尿核苷合成异胞苷衍生物的简便有效方法

本文报道从5'-O-磺酰基-2',3'-O-异亚丙基尿核苷通过一步法合成N-烷基2',3'-O-异亚丙基异胞苷和从5'-O-对甲苯磺酰基尿核苷合成5'-脱氧-5'-异丙氨基尿核苷。并对以上产物形成的机制作了探讨。     

Optimisation of polystyrene resin-supported Pt catalysts in room temperature, solvent-less, oct-l-ene hydrosilylation using methyldichlorosilane

Six precursor resins with systematic variation of porous parameters were prepared by suspension polymerisation using specific compositions of divinylbenzene, styrene vinylbenzyl chloride (VBC) and 2-ethylhexan-l-ol (a porogen). Surface areas from N(2) sorption and BET analysis were approximately 2-170 m(2)g-(1). The VBC content in each case was 38 mol% and these groups were aminated using the sodium salt of trimethylethylene diamine. Pt was introduced onto each resin at three different loadings (approximately 0.03, approximately 0.2 and approximately 0.4 mmol g-(1)) by appropriate manipulation of K(2)PtCl(6). The matrix of 18 resin-supported Pt complexes was then assessed for catalytic activity in the room temperature, solvent-less, hydrosilylation of oct-l-ene using methyldichlorosilane such that alkene: silane: Pt ratio was fixed at 2:1:1x10(-3). Though all the catalysts showed activity lower than that of homogeneous Speier s catalyst, most were sufficiently active to be potentially valuable heterogeneous catalysts in the laboratory, and indeed the plant. The most lightly loaded resins proved to be the least active. The remainder were recycled 5 times, and the best performers, the most highly loaded species, a further 5 times making 10 consecutive uses in all. A strong dependence on the porous structure of the resins was demonstrated with the activity rising systemically with the surface area. The two highest surface area highest loaded species displayed good activity even when used for the tenth time. The level of concurrent alkene isomerisation observed was very low throughout (<1%) making these heterogeneous species very selective as well as highly active. Overall the derived catalysts are excellent candidates for use in the research laboratory, and with further development could also be valuable in continuous processes.     

5′-脱氧-5′-氟-5-氟尿核苷的合成和性质

很多含氟核苷具有生理活性,因此,合成类似物引起人们的兴趣。5-氟尿核苷和5′-脱氧-5′-氟尿核苷的合成巳见报道。但是,5′-脱氧-5′-氟-5-氟尿核苷的合成及由于     

Synthesis of 3'-deoxynucleosides with 2-oxabicyclo[3.1.0]hexane sugar moieties: addition of difluorocarbene to a 3',4'-unsaturated uridine derivative and 1,2-dihydrofurans derived from D- and L-xylose1

Syntheses of 3'-deoxy analogues of adenosine, cytidine, and uridine with a 2,2-difluorocyclopropane ring fused at C3'-C4' are described. Treatment of a 2',5'-protected-3',4'-unsaturated derivative of uridine with difluorocarbene [generated from (CF3)2Hg and NaI] gave a diastereomeric mixture of the 3',4'-difluoromethylene compounds (alpha-L-arabino/beta-D-ribo, approximately 5:4). The limited stereoselectivity for addition at the beta face results from competitive steric hindrance by an allylic 4-methoxybenzyloxy group at C2' on the alpha face and a homoallylic nucleobase at C1' on the beta face. Protected uracil derivatives were converted into their cytosine counterparts via 4-(1,2,4-triazol-1-yl) intermediates. Treatment of 1,2-dihydrofurans derived from D- and L-xylose with difluorocarbene resulted in stereospecific addition at the beta face (anti to the 1,2-O-isopropylidene group on the alpha face). Glycosylations with activated enantiomeric sugar derivatives with the fused difluorocyclopropane ring on the beta face gave protected adenine nucleosides, whereas attempted glycosylation with an alpha-fused derivative gave multiple products. Removal of base- and sugar-protecting groups gave new difluoromethylene-bridged nucleoside analogues.     

Solid-phase parallel synthesis of 17alpha-substituted estradiol sulfamate and phenol libraries using the multidetachable sulfamate linker

We report an application of the multidetachable sulfamate linker in the synthesis of two model libraries of N-derivatized 17alpha-piperazinomethyl estradiols (phenols and sulfamates) by solid-phase parallel chemistry. The solid-phase precursor, a 3-sulfamoyl-17alpha-(N-trifluoroacetyl-piperazinomethyl) estradiol, was synthesized in solution from estrone and loaded efficiently onto trityl chloride resin as polymeric support. After cleavage of the trifluoroacetyl protecting group, sequential acylation reactions with five Fmoc-protected amino acids and five carboxylic acids were performed to introduce two levels of molecular diversity. Finally, the resins were split into two parts, and acidic (5% trifluoroacetic acid in dichloromethane) and nucleophilic (piperazine in tetrahydrofuran) cleavages were used to generate libraries A (5 x 5 sulfamates) and B (5 x 5 phenols) members in overall yields of 18-66% and high HPLC purities (87-96%) without purification steps. A preliminary screening test for inhibition of steroid sulfatase showed that the phenols were clearly weaker inhibitors, as compared to their sulfamate analogues. The most potent inhibitors were those with suitable hydrophobic amino acid and carboxylic acid substituents. Thus, compounds with a phenylalanine residue as the first element of diversity inhibited over 90% of steroid sulfatase activity at a concentration of 1 nM in homogenates of HEK-293 transfected cells, being as potent as the leading inhibitor 17alpha-tert-butylbenzyl estradiol 3-O-sulfamate previously reported. These results suggest that the steroid sulfatase inhibitory potency of estradiol derivatives, sulfamoylated or not, can be increased by the hydrophobic effect of a suitable substituent introduced in the proximity of the D ring of the steroid. The present work also demonstrated the efficiency and the cleavage versatility of the sulfamate linker to generate libraries of compounds with relevant biological importance, phenols and sulfamates.     

Intrastrand locks increase duplex stability and base pairing selectivity

Oligodeoxynucleotide probes with disulfide locks between neighboring nucleobases show increases in melting point for duplexes with RNA target strands of up to 7.6 °C. The weakly pairing TT dimers are replaced with locked 2'-deoxy-5-(thioalkynyl)uridine residues via automated synthesis.     

The sulfamate functional group as a new anchor for solid-phase organic synthesis

[reaction: see text] Sulfamate derivatives were loaded on trityl chloride resin, and two variants of cleavage were developed for this sulfamate anchor: an acid treatment to easily restore the free sulfamate and a nucleophilic treatment to generate the corresponding phenol. In addition to loading/cleavage assays and stability experiments, a model sequence of reactions was performed with the new sulfamate anchor to show its applicability in further combinatorial solid-phase synthesis of libraries of biologically relevant sulfamate derivatives.     

Synthesis, structure, and dynamics of six-membered metallacoronands and metallodendrimers of iron and indium

In the reaction of the N-substituted diethanolamines (H(2)L(1-3)) (1-3) with calcium hydride followed by addition of iron(III) or indium(III) chloride, the iron wheels [Fe(6)Cl(6)(L(1))(6)] (4) and [Fe(6)Cl(6)(L(2))(6)] (6) or indium wheels [In(6)Cl(6)(L(1))(6)] (5), [In(6)Cl(6)(L(2))(6)] (8) and [In(6)Cl(6)(L(3))(6)] (9) were formed in excellent yields. Exchange of the chloride ions of 6 by thiocyanate ions afforded [Fe(6)(SCN)(6)(L(2))(6)] (7). Whereas the structures of 4, 5 and 7 were determined unequivocally by single-crystal X-ray analyses, complexes 8 and 9 were characterised by NMR spectroscopy. Contrary to what is normally presumed, the scaffolds of six-membered metallic wheels are not generally rigid, but rather undergo nondissociative topomerisation processes. This was shown by variable temperature (VT) (1)H NMR spectroscopy for the indium wheel [In(6)Cl(6)(L(1))(6)] (5) and is highlighted for the enantiotopomerisation of one indium centre [ 1/6[S(6)-5]<==>[1/6[S(6)-5']]. The self-assembly of metallic wheels, starting from diethanolamine dendrons, is an efficient strategy for the convergent synthesis of metallodendrimers.     

2,5-取代-1,3,4-噁二唑化合物库的固相合成

本文使用组合化学方法以聚苯乙烯亚磺酸钠树脂（1）为载体合成了2，5-取代-1，3，4-二唑化合物库。树脂1首先与溴代乙酸乙酯反应生成聚合物支载的乙酸酯（2）。肼解后所得的肼树脂进一步与取代的苄氯反应得双欧讲树脂（4）。树脂4与三氯氧磷回流得聚合物支载的2，5-取代-1，3，4-二唑（5）。用W-溴代乙酰苯酮烷基化后聚合物支载的产物用三乙胺解脱得2-芳基-5-芳甲酰亚乙烯基-1，3，4-二唑化合物库，产率15％-36％。