Synthesis and use of <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-di-Boc-glutamate γ-semialdehydes and related aldehydes

Summary.  This review article focuses on the synthesis and reactions of N,N-di-Boc glutamate and aspartate semialdehydes as well as related aldehydes. These building blocks are prepared according to various strategies from glutamic and aspartic acids and find interesting synthetic applications. In the first part, the methods for the synthesis of N,N-di-Boc-amino aldehydes are summarized. The applications of these chiral synthons for the synthesis of unnatural amino acids and other bioactive compounds are discussed in the second section. Received April 24, 2002 Accepted August 13, 2002 Published online January 30, 2003 Authors' address: Prof. Violetta Constantinou-Kokotou, Chemical Laboratories, Agricultural University of Athens, Iera Odos 75, 11855 Athens, Greece, E-mail: vikon@aua.gr Abbreviations: AcNH-TEMPO, 4-acetamido-2,2,6,6-tetramethyl-1-piperidinyloxy free radical; AIBN, 2,2′-azobis(2-methylpropionitrile); Aliquat, methyltrioctylammonium chloride; Bn, benzyl; Boc, tert-butoxycarbonyl; Bu^t, tert-butyl; m-CPBA, 3-chloroperoxybenzoic acid; DAST, diethylaminosulfur trifluoride; DBU, 1,8-diazabicyclo[5.4.0]undec-7-ene; (R,R)-(+)-DET, (R,R)-(+)-diethyltartrate; DIBALH, diisobutyl aluminium hydride; DMAP, 4-dimethylaminopyridine; DMF, dimethylformamide; Et₃N, triethylamine; KHMDS, potassium bis(trimethylsilyl)amide; (S)-LLB, lanthanium-lithium-bis-metallic binaphthol catalyst; MsCl, methanesulfonyl chloride; NEM, N-ethylmorpholine; NMO, 4-methylmorpholine N-oxide; PPA, propylphosphonic acid anhydride; TBHP, tert-butyl hydroperoxide; TFA, trifluoroacetic acid; THF, tetrahydrofuran; TMSI, 1-(trimethylsilyl)imidazole; Trt, trityl.     

An Efficient Method for the Synthesis of β-d-Ribonucleosides Catalyzed by Metal Iodides

Abstract

Several β-d-ribonucleosides were synthesized in high yields under mild conditions by N-glycosylations of methyl 2,3,5-tri-O-benzoyl-β-d-ribofuranosyl carbonate (1) with trimethylsilylated nucleoside bases in acetonitrile using a catalytic amount of metal iodide such as SnI₂, SbI₃ or TeI₄. A deprotection of N⁶ -benzoyl group of coupling product took place to a considerable extent when N⁶ -benzoyl-N⁶ , N⁹ -bis(trimethylsilyl)adenine was employed as a nucleoside base using SnI₂ or SnCI₂ as a catalyst while it was minimized when SbI₃ or TeI₄ was used. Further, the N-glycosylation of 1 with 7-trimethylsilyltheophylline in the presence of a catalytic amount of metal iodide was more effectively achieved in nitrile solvents other than acetonitrile.

     

Nα-Fmoc-O,O-(dimethylphospho)-L-tyrosine fluoride: A convenient building block for the solid-phase synthesis of phosphotyrosyl peptides

Summary Fmoc-O,O-(dimethylphospho)-l-tyrosine was converted into stable Fmoc-O,O-(dimethylphospho)-L-tyrosine fluoride by means of (diethylamino) sulfur trifluoride or cyanuric fluoride. This building block was used for efficient coupling of phosphotyrosine to the adjacent sterically hindered amino acid Aib or Ac₆c in, model peptide sequences as well as for the synthesis of the ‘difficult’ phosphotyrosine peptide Stat91^695–708. The phosphate methyl groups were cleaved on solid phase after peptide assembly by means of trimethylsilyl iodide in MeCN. Aib, α-aminoisobutyric acid Ac₆c, 1-amino-cyclohexyl-l-carboxylic acid; BOP, benzotriazol-l-yl-oxy-tris(dimethylamino) phosphonium hexafluorophosphate, CIP, 2-chloro-l, 3-dimethylimidazolidium hexafluorophosphate, DAST, (diethylamino)sulfur trifluoride; DBU 1,8-diazabicyclo[5.4.0]undec-7-ene; DCM, dichloromethane; DIEA, drisopropylethylamine; DMA dimethylacetamide; Fmoc, 9-fluorenylmethoxycarbonyl; HATU,O-(7-azabenzotriazol-l-yl)-1.1,3,3-tetramethyluronium hexafluorophosphate; HOAt, I-hydroxy-7-azabenzotriazole; HOBt,N-hydroxybenzotriazole; HPLC, high-performance liquid chromatography; MBHA, 4-methylbenzhydrylamine; MeCN, acetonitrile; NMP,N-methyl-2-pyrrolidinone; NMR, nuerear magnetic resonance; PS, polystyrene; PyBroP, bromotris(pyrrolidino)phosphonium hexafluorophosphate; Rink amide MBHA-PS, 4-(2′,4′-dimethoxyphenyl-Fmoc-aminophenyl)-phenoxyacetamido-norleucyl-MBHA-PS; TFA, trifluoroacetic acid; TMSI, trimethylsilyl iodide; TPTU, 2-(2-pyridon-l-yl)-1,1,3,3-tetramethyluroniumfluoroborate; t_R, retention time; UNCA, arethane-protected amino acidN-carboxy anhydride Abbreviations for amino acids and nomenclature of, peptide structures follow the recommendations of the IUPAC-IUB Commission on Biochemical Nomenclature [Eur. J. Biochem., 138 (1984) 9].     

3,5,2',4'-Tetrahydroxychalcone, a new non-purine xanthine oxidase inhibitor

Xanthine oxidase is a key enzyme that catalyses hypoxanthine and xanthine to uric acid and the overproduction of uric acid will lead to hyperuricemia which is an important cause of gout. In the present study, three chalcone derivatives were synthesized and evaluated for inhibitory activity against xanthine oxidase in vitro. Of the compounds, only Compound 1, 3,5,2′,4′-tetrahydroxychalcone, exhibited a significant inhibitory activity on xanthine oxidase with an IC₅₀ value of 22.5 μM. Lineweaver–Burk transformation of the inhibition kinetics data demonstrated that it was a competitive inhibitor of xanthine oxidase and Ki value was 17.4 μM. In vivo, intragastric administration of Compound 1 was able to significantly reduce serum uric acid levels and inhibited hepatic xanthine oxidase activities of hyperuricemic mice in a dose-dependent manner. Acute toxicity study in mice showed that Compound 1 was very safe at a dose of up to 5 g/kg. These results suggest that Compound 1 is a novel competitive xanthine oxidase inhibitor and is worthy of further development.     

Method for the Synthesis of Uric Acid Derivatives

Abstract

A general procedure to obtain tetra-substituted uric acid by stepwise N-alkylation is described. 2,6-Dichloropurine (1) was condensed with 1-propanol by Mitsunobu reaction to give 9-propyl congener (2). Treatment of 2 with ammonia gave adenine derivative (4a), which was converted to the 8-oxoadenine (5b) in 3 steps. Methylation of 5b proceeded site-specifically to give 6-amino-2-chloro-7,8-dihydro-7-methyl-9-propylpurin-8-one (6) as a sole product. Compound 6 was successively treated with NaNO₂ and iodomethane to give 2-chloro-1,6,7,8-tetrahydro-1,7-dimethyl-9-propylpurin-6,8-dione (9) accompanied by the O ⁶-methyl product (8) in 75% and 6.9%, respectively. After nucleophilic substitution of 9 with NaOAc, the product (11) was reacted with iodomethane to give the uric acid (12) and the 2-methoxy product (13) in 46% and 15.5%, respectively. However, the reaction of 11 with the benzylating agents gave only O-benzyl products (14a,b).     

Novel 1,3,2-diazabora-[3]ferrocenophanes and a 1,4,2,3-diazadibora-[4]ferrocenophane

N,N′-Dilithiated 1,1′-bis(trimethylsilylamino)ferrocene (2) reacts with boron halide adducts (HBBr₂-SMe₂; BF₃-OEt₂ and BBr₃-SMe₂), boron halides (BCl₃, BBr₃, BCl₂(OPh) and BCl₂(Ph)) and 1,1-bis(dimethylamino)dichlorodiborane(4) to give the corresponding 1,3-bis(trimethylsilyl)-1,3,2-diazabora-[3]ferrocenophanes (3)-(8) and the 2,3-bis(dimethylamino)-1,4-bis(trimethylsilyl)-1,4,2,3-diazadibora-[4]ferrocenophane (9). All new complexes were characterised by multinuclear magnetic resonance spectroscopy in solution, and the solid-state molecular structures of the hydride (3), fluoride, chloride (4, 5), and of the phenoxy and phenyl derivatives (7, 8) were determined by X-ray analysis.     

A practical dealkylation procedure for O,O-dimethyl-phosphotyrosyl-containing peptide-resins

Summary This paper gives a useful protocol for the demethylation of O,O-dimethyl-phosphotyrosyl peptides on solid support by means of trimethylsilyl iodide in acetonitrile. The method is demonstrated to be well suited for peptide sequences containing arginine, histidine, methionine and tryptophan.Abbreviations DBU 1,8-diazabicyclo[5.4.0]undec-7-ene - DIEA diisopropylethylamine - DMA dimethylacetamide - EDT 1,2-ethanedithiol - EGF epidermal growth factor - ESI-MS electrospray ionisation mass spectrometry - Fmoc 9-fluorenylmethoxycarbonyl - HPLC high-performance liquid chromatography - MBHA 4-methyl-benzhydrylamine - NMP N-methyl-2-pyrrolidinone - NMR nuclear magnetic resonance - TFA trifluoroacetic acid - TMSBr trimethylsilyl bromide - TMSCI trimethylsilyl chloride - TMSI trimethylsilyl iodide - TMSOTf trimethylsilyl trifluoromethanesulfonate - TPTU 2-(2-pyridon-1-yl)-1,1,3,3-tetramethyluroniumfluoroborate - t_R retention time Abbreviations for amino acids and nomenclature of peptide structures follow the recommendations of the IUPAC-IUB Commission on Biochemical Nomenclature [Eur. J. Biochem., 138 (1984) 9].     

Chemical composition of cornicle secretion of the brown citrus aphid Toxoptera citricida

Brown citrus aphid Toxoptera citricida Kirkadly is considered as an important pest of citrus because it vectors citrus tristeza closterovirus. Aphids secrete a fluid from their cornicles as a defensive mechanism against natural enemies. Earlier studies on cornicle secretions of aphids focus only on triglycerides and fatty acids. In the present study, three different methods are used to investigate the chemical composition of the cornicle fluid of T. citricida. Gas chromatography with flame ionization detection is used to detect and quantify the triglycerides after trimethylsilyl derivatization, and gas chromatography‐mass spectrometry (GC‐MS) is used to determine the fatty acid composition after derivatization with boron trifluoride–methanol. Other compounds are detected using GC‐MS after methoxyamine hydrochloride and N‐methyl‐N‐(trimethylsilyl)trifluoroacetamide derivatization. The major fatty acid in the cornicle secretion of T. citricida is palmitic acid. Oleic, stearic, myristic, myristoleic and sorbic acids are also detected, although in low amounts. Sorboyl, dipalmitoyl (C_6‐2, C₁₆, C₁₆) and disorboyl, stearoyl (C_6‐2, C_6‐2, C₁₈) are the main triglycerides detected in cornicle secretion. Trehalose is the most predominant sugar (558.2 mm ), followed by glucose (92.0 mm ) and inositol (48.8 mm ). Many amino acids, including proline, glycine, alanine and serine, are also detected. In addition, the cornicle secretion is rich in many organic acids, including malic, citric, succinic and lactic acid. Information obtained from the present study improves our understanding of the chemical composition of the cornicle secretion of the brown citrus aphid.     

Facile Synthesis of N-(1-Alkenyl) Derivatives of 2,4-Pyrimidinediones

Abstract

N-(1-alkenyl) derivatives of 2,4-pyrimidinediones (6–9) were prepared in a one pot synthesis from aldehydes and the nucleobases using trimethylsilyl trifluoromethanesulfonate (TfOTMS) as coupling reagent. Presilylation of the above nucleobases, and N ⁶-benzoyladenine, with excess N,O-bis(trimethylsilyl)acetamide (BSA) followed by addition of one mol eq. TfOTMS yielded the N-(1-trimethylsilyloxyalkyl) derivatives 1–5.     

Determination of N-acetylneuraminic acid by gas chromatography-mass spectrometry with a stable isotope as internal standard

N-Acetylneuraminic acid was determined by gas chromatography-mass spectrometry using selected ion-monitoring technique with N-[²H₃]acetylneuraminic acid as an internal standard. M-COOTMS fragments at $\text{m}\text{z}$ 624 of trimethylsilyl derivatives of N-acetylneuraminic acid and at $\text{m}\text{z}$ 627 of that of the internal standard were used as monitoring ions. The standard curve obtained was linear in the range of over 10³, and the lower limit for quantitation was estimated to be a few hundred picograms. This method was used to measure total N-acetylneuraminic acid in the plasma of healthy humans and patients with lung cancer. The total N-acetylneuraminic acid level in the plasma was two to three times higher in the patients than in controls. A few hundred nanoliters of plasma was sufficient for the analysis. The mass fragmentogram of plasma gave a good signal/noise ratio, and measurements were very specific, accurate, and reproducible.     

SYNTHESIS AND ANTIVIRAL ACTIVITY OF NOVEL EXOMETHYLENE CYCLOPROPYL NUCLEOSIDES

Novel cyclopropyl nucleosides were synthesized as potential antiviral agents. The key intermediate 5, prepared from Feist's acid 1 was condensed with purine derivatives by the S_N2 type reaction. All the synthesized compounds were evaluated for antiviral activity.     

Synthesis and bioactivity of 5-(1-aryl-1H-tetrazol-5-ylsulfanylmethyl)-N-xylopyranosyl-1,3,4-oxa(thia)diazol-2-amines

A series of new N′-[N-(2,3,4-tri-O-acetyl-β-d-xylopyranosyl)thiocarbamoyl]-2-[(1-aryl-1H-tetrazol-5-yl)sulfanyl]acetohydrazides 5a–5e were synthesized rapidly in high yields from 2-(1-aryl-1H-tetrazol-5-ylsulfanyl)acetohydrazides 3a–3e and 2,3,4-tri-O-acetyl-β-d-xylopyranosyl isothiocyanate 4, then 5a–5e were converted to a series of new 5-(1-aryl-1H-tetrazol-5-ylsulfanylmethyl)-N-(2,3,4-tri-O-acetyl-β-d-xylopyranosyl)-1,3,4-oxadiazole-2-amines 6a–6e and 5-(1-aryl-1H-tetrazol-5-ylsulfanylmethyl)-N-(2,3,4-tri-O-acetyl-β-d-xylopyranosyl)-1,3,4-thiadiazole-2-amines 7a–7e, respectively under mercuric acetate/alcohol system or acetic anhydride/phosphoric acid system, then deacetylated in the solution of CH₃ONa/CH₃OH. All of the novel compounds were characterized by IR, ¹H NMR, ¹³C NMR, MS and elemental analysis. The structures of compounds 2e, 3e, 5a and 5c have been determined by X-ray diffraction analysis. Some of the synthesized compounds displayed PTP1B inhibition and microorganism inhibition.     

Synthesis and anticancer activity of 3′-[4-fluoroaryl-(1,2,3-triazol-1-yl)]-3′-deoxythymidine analogs and their phosphoramidates

Abstract

A series of novel 4-chlorophenyl N-alkyl phosphoramidates of 3′-[4-fluoroaryl-(1,2,3-triazol-1-yl)]-3′-deoxythymidines (20–49) was synthesized by means of phosphorylation of 3′-[4-aryl-(1,2,3-triazol-1-yl)]-3′-deoxythymidines (7–11) with 4-chlorophenyl phosphoroditriazolide (14), followed by a reaction with the appropriate amine. The synthesized compounds 7–11 and 20–49 were evaluated along with four known anticancer compounds for their cytotoxic activity in human cancer cell lines: cervical (HeLa), nasopharyngeal (KB), breast (MCF-7), osteosarcoma (143B) (only selected compounds 20, 24, 28, 32–36, 38, 40, 46) and normal human dermal fibroblast cell line (HDF) using the sulforhodamine B (SRB) assay. Among 3′-[4-aryl-(1,2,3-triazol-1-yl)]-3′-deoxythymidines (7–11) the highest activity in all the investigated cancer cells was displayed by 3′-[4-(3-fluorophenyl)-(1,2,3-triazol-1-yl)]-3′-deoxythymidine (9) (IC₅₀ in the range of 2.58–3.61?μM) and its activity was higher than that of cytarabine. Among phosphoramidates 20–49 the highest activity was demonstrated by N-n-propyl phosphoramidate of 3′-[4-(3-fluorophenyl)-(1,2,3-triazol-1-yl)]-3′-deoxythymidine (35) in all the cancer cells (IC₅₀ in the range of 0.97–1.94?μM). Also N-ethyl phosphoramidate of 3′-[4-(3-fluorophenyl)-(1,2,3-triazol-1-yl)]-3′-deoxythymidine (33) exhibited good activity in all the used cell lines (IC₅₀ in the range of 4.79–4.96?μM).     

Oxetanocin—Oxetanose Chemistry: Lewis Acid Promoted Glycosidations of the D-Erythrooxetanose Derivatives

Abstract

Upon treatment of 1-O-acetyl-D-erythrooxetanoses (17a,b and 26) with trimethylsilyl N-benzoyladenine or allyltrimethylsilane in the presence of SnCl₄, the ring expanded products (18, 19 and 29) or the acyclic compounds (27 and 28) were obtained. The reaction mechanism involving a novel ring opening process is discussed.     

An amperometric uric acid biosensor based on multiwalled carbon nanotube-gold nanoparticle composite

An amperometric uric acid biosensor was fabricated by immobilizing uricase (EC 1.7.3.3) onto gold nanoparticle (AuNP)/multiwalled carbon nanotube (MWCNT) layer deposited on Au electrode via carbodiimide linkage. Determination of uric acid was performed by oxidation of enzymically generated H₂O₂ at 0.4 V. The sensor showed optimal response within 7 s at 40 °C in 50 mM Tris–HCl buffer (pH 7.5). The linear working range of the biosensor was 0.01–0.8 mM. The limit of detection (LOD) was 0.01 mM. The sensor measured uric acid levels in serum of healthy individuals and persons suffering from gout. The analytical recoveries of the added uric acid, 10 and 20 mg L^–1, were 98.0% and 96.5%, respectively. Within- and between-batch coefficients of variation were less than 5.6% and less than 4.7%, respectively. A good correlation (r = 0.998) was obtained between serum uric acid values by the standard enzymic colorimetric method and the current method. A number of serum substances had practically no interference. The sensor was used in more than 200 assays and had a storage life of 120 days at 4 °C.     

Purification and Characterization of Novel N-Acyl-D-aspartate Amidohydrolase from Alcaligenes xylosoxydans subsp. xylosoxydans A-6

Alcaligenes xylosoxydans subsp. xylosoxydans A-6 (Alcaligenes A-6) produced N-acyl-D-aspartate amidohydrolase (D-AAase) in the presence of N-acetyl-D-aspartate as an inducer. The enzyme was purified to homogeneity. The enzyme had a molecular mass of 56 kDa and was shown by sodium dodecyl sulfate (SDS)–polyacrylamide gel electrophoresis (PAGE) to be a monomer. The isoelectric point was 4.8. The enzyme had maximal activity at pH 7.5 to 8.0 and 50°C, and was stable at pH 8.0 and up to 45°C. N-Formyl (K_m=12.5 mM), N-acetyl (K_m=2.52 mM), N-propionyl (K_m=0.194 mM), N-butyryl (K_m=0.033 mM), and N-glycyl (K_m =1.11 mM) derivatives of D-aspartate were hydrolyzed, but N-carbobenzoyl-D-aspartate, N-acetyl-L-aspartate, and N-acetyl-D-glutamate were not substrates. The enzyme was inhibited by both divalent cations (Hg²⁺, Ni²⁺, Cu²⁺) and thiol reagents (N-ethylmaleimide, iodoacetic acid, dithiothreitol, and p-chloromercuribenzoic acid). The N-terminal amino acid sequence and amino acid composition were analyzed.     

Synthesis,antitumour and antioxidant activities of novel α,β-unsaturated ketones and related heterocyclic analogues: EGFR inhibition and molecular modelling study

New α,β-unsaturated ketones 4a,b; 5a–c; and 6a,b; as well as 4-H pyran 7; pyrazoline 8a,b; isoxazoline 9; pyridine 10–11; and quinoline-4-carboxylic acid 12a,b derivatives were synthesized and evaluated for in vitro antitumour activity against HepG2, MCF-7, HeLa, and PC-3 cancer cell lines. Antioxidant activity was investigated by the ability of these compounds to scavenge the 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS^?+). Compounds 6a, 6b, 7, and 8b exhibited potent antitumour activities against all tested cell lines with [IC₅₀] ?5.5–18.1 µΜ), in addition to significantly high ABTS^?+ scavenging activities. In vitro EGFR kinase assay for 6a, 6b, 7, and 8b as the most potent antitumour compounds showed that; compounds 6b, and 7 exhibited worthy EGFR inhibition activity with IC₅₀ values of 0.56 and 1.6?µM, respectively, while compounds 6a and 8b showed good inhibition activity with IC₅₀ values of 4.66 and 2.16?µM, respectively, compared with sorafenib reference drug (IC₅₀?=?1.28?µM). Molecular modelling studies for compounds 6b, 7, and 8b were conducted to exhibit the binding mode towards EGFR kinase, which showed similar interaction with erlotinib.     

Modeling carbon monoxide dehydrogenase/acetyl-CoA synthase (CODH/ACS): a trinuclear nickel complex employing deprotonated amides and bridging thiolates

Carbon monoxide dehydrogenase/acetyl-CoA synthase (CODH/ACS) utilizes a unique Ni-M bimetallic site in the biosynthesis of acetyl-CoA, where a square-planar Ni ion is coordinated to two thiolates and two deprotonated amides in a Cys-Gly-Cys motif. The identity of M is currently a matter of debate, although both Cu and Ni have been proposed. In an effort to model ACSs unusual active site and to provide insight into the mechanism of acetyl-CoA formation and the role of each of the metals ions, we have prepared and structurally characterized a number of Ni(II)–peptide mimic complexes. The mononuclear complexes Ni(II) N,N-bis(2-mercaptoethyl)oxamide (1), Ni(II) N,N-ethylenebis(2-mercaptoacetamide) (2), and Ni(II) N,N-ethylenebis(2-mercaptopropionamide) (3) model the Ni(Cys-Gly-Cys) site and can be used as synthons for additional multinuclear complexes. Reaction of 2 with MeI resulted in the alkylation of the sulfur atoms and the formation of Ni(II) N,N-ethylenebis(2-methylmercaptoacetamide) (4), demonstrating the nucleophilicity of the terminal alkyl thiolates. Addition of Ni(OAc)₂·4H₂O to 3 resulted in the formation of a trinuclear species 5, while 2 crystallizes as an unusual paddlewheel complex (6) in the presence of nickel acetate. The difference in reactivity between the similar complexes 2 and 3 highlights the importance of ligand design when synthesizing models of ACS. Significantly, 5 maintains the key features observed in the active site of ACS, namely a square-planar Ni coordinated to two deprotonated amides and two thiolates, where the thiolates bridge to a second metal, suggesting that 5 is a reasonable structural model for this unique enzyme.Ø. Hatlevik and M.C. Blanksma contributed equally to this work     

Acid-labile handles for Fmoc solid-phase synthesis of peptide N-alkylamides

Summary By analogy to established methodology for the preparation of C-terminal peptide amides by 9-fluorenylmethyl-oxycarbonyl (Fmoc) chemistry, in conjunction with the acidolyzable 5-(4-Fmoc-aminomethyl-3,5-dimethoxyphenoxy)valeric acid (PAL, 1) handle, the present paper reports on 5-(4-(N-Fmoc-N-alkyl)aminomethyl-3,5-dimethoxyphenoxy)valeric acid [(R)PAL, 2] handles that can be used for synthesis of peptide N-alkylamides. The key step in the preparation of these handles was the NaBH₃CN-mediated reductive amination (60 to 85% yields; R=CH₃, CH₃CH₂, C₆H₅CH₂CH₂, 4-NO₂C₆H₅) of 5-(4-formyl-3,5-dimethoxyphenoxy)valeric acid (4), an aldehyde precursor to PAL. The (R)PAL handles (2a and b) were applied to the preparation of LHRH analogues. After anchoring of handles to PEG-PS supports, peptide chain assemblies were carried out, and treatments with TFA-thioanisolephenol-1,2-ethanedithiol (87:5:5:3) for 90 min at 25 °C, followed by aqueous workups, provided the expected products in excellent yields and purities as supported by HPLC and mass spectrometric characterization.Taken in part from the Ph.D. Thesis of M.F. Songster, University of Minnesota, 1996. Preliminary reports of this work were presented at the 14th American Peptide Symposium, Columbus, OH, June 18–23, 1995 (poster P047), and at the Fourth International Symposium on Solid Phase Synthesis and Combinatorial Chemical Libraries, Edinburgh, Scotland, UK, September 12–16, 1995.     

Design and Synthesis of LNA-Based Mercaptoacetamido-Linked Nucleoside Dimers

Three LNA-based mercaptoacetamido-linked nonionic nucleoside dimers T^L-S-T, T-S-T^L , and T^L-S-T^L have been synthesized by HOBT and HBTU catalyzed condensation of silyl-protected 2-S-(thymidin-5?′-yl)mercaptoacetic acid or 2-S-(2?′-O,4?′-C-methylenethymidin-5?′-yl)mercaptoacetic acid with 3?′-amino-3?′-deoxy-5?′-O-DMT-2?′-O,4?′-C-methylenethymidine or with 3?′-amino-3?′-deoxy-5?′-O-DMT-β-thymidine followed by desilylation of the protected dimers. The 3?′-O-phosphoramidite derivative of one of the nucleoside dimers was successfully prepared by condensation with [P(-Cl)(-OCH₂CH₂CN)-N(iPr)₂}] in DCM in the presence of N,N-diisopropylethylamine (DIPEA), which is a building block for the preparation of mercaptoacetamido-linked oligonucleotides of therapeutic applications.