摘要:

AbstractThree macrobicyclic octamines1–3and the macrotricyclic hexadecamine14have been synthesized. The octamines1–3bind anionic substrates when protonated. The stability constants of the complexes between the protonated forms of the macrobicyclic polyamines and halide anions have been determined by pH‐metric measurements. The stability constants in H2O are very high;1in its hexaprotonated form binds F−with high selectivity (selectivity F−/Cl−>108), while3exhibits strong stability constants for both F−and Cl−. Three X‐ray structures have been obtained, one where F−is held inside the cavity of1· 6H+, one where Cl−is included in3· 6H+, and3· 6H+w

ISSN:0018-019X    

DOI:10.1002/hlca.19960790302

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractFour cyclotetrapeptides containing one (1, 2) or two (3, 4) chiral amino acids have beenC‐alkylated orC‐hydroxyalkylated through Li+or phosphazenium (P4 · H+) enolates. The reactions are completely diastereoselective (by NMR or HPLC analysis) with respect to the newly formed backbone stereogenic centres (Tables 2and3). The reactivity of the polylithiated species responsible for these alkylations is such that only highly reactive electrophiles (MeI, BnBr, primary allylic halides, aldehydes, CO2) can be employed. It is shown that the position, and thus the chirality sense, of the newly formed stereogenic centre in a given cyclotetrapeptide backbone is controlled by the positioning ofN‐methyl groups in the starting material (cf.cyclo(‐MeLeu‐Gly‐D‐Ala‐Sar‐) (3) and cyclo(‐Leu‐Sar‐MeDAla‐Gly‐) (4) inScheme 1). WithSchwesinger's phosphazene P4‐base, all NH groups are first benzylated andC‐benzylation then takes place at a sarcosine, rather than anN‐benzylglycine residue (Table 3). In contrast to open‐chainN‐benzyl peptides, theN‐benzylated cyclotetrapeptides could not be debenzylated under dissolving‐metal conditions (Na/NH3). Conformational analysis (NMR spectroscopy and X‐ray diffraction) shows that the prevailing species havecis/trans/cis/trans(ctct)peptide bonds (zigzag conformation ofCibackbone symmetry,Figs. 2–4). However, a hitherto unknown conformation of cyclotetrapeptides has been found in CDCl3solutions of the hydroxyalkylated products18–21(obtained with EtCHO and PhCHO as electrophiles;Fig.4). The new conformation has fourtranspeptide bonds and is believed to result mainly from intramolecular H‐bond formation, involving the newly generated alkyl‐ or arylserine residue. This assumption has also been supported by modelling (TRIPOS force field, SYBYL, seeFig.5andTable 6

ISSN:0018-019X    

DOI:10.1002/hlca.19960790303

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractMonomeric 3′‐deoxyadenosine (cordycepin) was modified at the 2′‐O‐ (13–18) and 5′‐O‐position (25–29) by the vitamins E, D2, and A and by the two lipids 1,2‐di‐O‐palmitoylglycerol and 1,2‐di‐O‐hexadecylglycerolviasuccinate or carbonate linkages. The base‐labile conjugates afforded protection groups like the 2‐(4‐nitro‐phenyl)ethoxycarbonyl (npeoc) and monomethoxytrityl group (MeOTr) that are cleavable without harming the ester and carbonate bonds, respectively. Monomeric conjugates of cordycepin and vitamin E, vitamin D2, 1,2‐di‐O‐palmitoylglycerol, and 1,2‐di‐O‐hexadecylglycerol (see13, 14, 17, 18, 25, 26, 28, and29) inhibited HIV‐1‐induced syncytia formation 1.7 to 6.2 fold compared to 1.5‐fold for cordycepin (seeTable);IC50values for25and28were 257 and 267 m̈M, respectively. In addition, the monomeric cordycepin‐vitamin and ‐lipid conjugates inhibited HIV‐1 RT activity 28–49% which compares with a 13% inhibition of HIV‐1 RT observed for cordycepin. The minimal inhibition of HIV‐1‐induced syncytia formation and HIV‐1 RT activity did not proceed by the activation of

ISSN:0018-019X    

DOI:10.1002/hlca.19960790304

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractThe syntheses of biodegradable 2′‐ and 5′ ‐ester and 2′‐ and 5′ ‐carbonate conjugates of the antivirally active 3′‐deoxyadenylyl‐(2′–5′)‐3′‐deoxyadenylyl‐(2′–5′)‐3′‐deoxyadenosine (cordycepin‐trimer core) with the vitamins, E, D2, and A and the lipids 1,2‐di‐O‐palmitoylglycerol and 1,2‐di‐O‐hexadecylglycerol were achieved first by preparation of the trimeric educts19–21(Scheme 1). Secondly, these substances were condensed with the lipophilic residuesviaa succinate or carbonate linker and then deprotected by β‐elimination of the npeoc and npe protecting groups and acid treatment for detritylation without harming the ester and carbonate functions, respectively (Scheme 2). Metabolically stable cordycepin‐trimer‐vitamin and ‐lipid conjugates are a new class of bioconjugates that inhibit HIV‐1‐induced syncytia formation withIC50values of 7, 18, and 24 m̈Mfor39, 29, and42, respectively, and inhibit HIV‐1 reverse transcriptase (RT) activity from 14 to 96% (seeTable). Of the nine conjugates tested, inhibition of HIV‐1 replication by28, 29, 32, 40, and42may be attributed in part to the activation of the RNase L/PKR antiviral pathways. Trimer conjugate42showed the greatest inhibition of HIV‐1 replication,i.e., a 120‐fold decrease in HIV‐1‐induced syncytia formation and an 88% inhibition of HIV‐1 reverse transcriptase (RT). This inhibition of replication of HIV‐1 by42can be attributed in part to the activation of recombinant, human RNase L. The inhibition of HIV‐1 replication by the cordycepin‐trimer‐vitamin and ‐lipid conjugate

ISSN:0018-019X    

DOI:10.1002/hlca.19960790305

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractThe synthesis of functionalized 1,1,2,2‐tetraethynylethanes (= 3,4‐diethynylhexa‐1,5‐diynes) as synthons for tetraethynylethenes (3,4‐diethynylhex‐3‐ene‐1,5‐diynes) and as building blocks for three‐dimensional acetylenic molecular scaffolding targeting the synthesis of the molecular carbon belts3and4is reported (Scheme 1). Reaction of diethyl oxalate and (trialkylsilyl)ethynylGrignardreagents afforded the silyl‐protected 3,4‐diethynylhexa‐1,5‐diyne‐3,4‐ diols7and8which were transformed in high yields into the cyclic carbonate9and the cyclic orthoesters10–13, respectively (Scheme 2). The solid‐state structures of9and10were elucidated by X‐ray crystallography. The alkyne protecting groups in9, 10, and12were smoothly removed to give the free tetraynes14–16as relatively stable oils in nearly quantitative yields (Scheme 3). Orthoesters15and16underwent Pd‐catalyzed cross‐coupling with iodobenzene to give the tetraphenyl derivatives17and18(Scheme 4). Thermal acid‐catalyzed elimination of the orthoester moieties in12and13produced the silyl‐protected tetraethynylethenes19and20and concluded a novel, simple three‐step synthesis of these fully two

ISSN:0018-019X    

DOI:10.1002/hlca.19960790306

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

Perrhenate‐Catalyzed Rearrangement of Ethinyl‐β‐ionolThe rearrangement of 2‐ethinyl‐β‐ionol (1) to α,β‐unsaturated carbonyl compounds using tetraalkylammonium perrhenate catalysts was studied. It was found that theRupe‐Kambliproduct, ketone2, is the main product (ca.70%) of this rearrangement. The by‐product4(ca.15%) is formed in a

ISSN:0018-019X    

DOI:10.1002/hlca.19960790307

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractIn a search for the inhibitors of platelet aggregation, certain coumarin derivatives were synthesized and evaluated for antiplatelet activity against thrombin(Thr)‐, arachidonic acid(AA)‐, collagen(Col)‐, and platelet‐activating‐factor(PAF)‐induced aggregation in washed rabbit platelets. These compounds were synthesized from 4‐hydroxycoumarin (1) or naphthalen‐1‐olviaalkylation andReformatsky‐type condensation (Schemes 1–3). Among them, 4‐[(2,3,4,5‐tetrahydro‐4‐methylidene‐5‐oxo‐2‐phenylfuran‐2‐yl)methoxy]‐2H‐1‐benzopyran‐2‐one (6b) showed potent antiplatelet effects on AA‐ and PAF‐induced aggregation withIC50values of 8.21 and 103.67 m̈M, respectively (seeTables 1and2). The antiplatelet potency of6bagainst PAF‐induced aggregation could be further improved by introducing a pr

ISSN:0018-019X    

DOI:10.1002/hlca.19960790308

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

An Alternative Approach to the PQQ‐TriesterA novel approach to triethyl 5‐methoxy‐1H‐pyrrolo[2,3‐f]quinoline‐2,7,9‐tricarboxylate (6), a close precursor of the redox cofactor PQQ of bacterial dehydrogenases, is described. Diethyl 2‐oxopent‐3‐ynedioate (5) was used as building block for the annelation of the quinoline unit. The annelation proceeds in two stepsviathe diastereoselective formation of diethyl (Z)‐4‐{[2‐(ethoxycarbonyl)‐5‐methoxyindol‐6‐yl]amiono}‐2‐oxopent‐3‐enedioate ((Z)‐7) f

ISSN:0018-019X    

DOI:10.1002/hlca.19960790309

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractThe triazenols 4‐R1C6H4NNN(OH)R2(1), oxidized witht‐BuO ⋅2radicals, produced nitroxide radicals R1C6H4N(O⋅)NN(R2)+O−(5). The suggested radical structure was confirmed by15N‐labeling. The reaction of triazenols1with PbO2proceeded under N2elimination, in which case nitroxides R1C6H4N(R2)O⋅(2) were observed as the final radical products. The intermediate R1C6H 

ISSN:0018-019X    

DOI:10.1002/hlca.19960790310

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

Monodisperse Linear and Cyclic Oligo[(R)‐3‐hydroxybutanoates] Containing up to 128 Monomeric UnitsUsing benzyl ester/(tert‐butyl)diphenylsilyl ether protection, (COCl)2/pyridine esterification conditions, and a fragment‐coupling strategy (with H2/Pd‐C debenzylation and HF · pyridine desilylation), linear oligomers of (R)‐3‐hydroxybutanoic acid (3‐HB) containing up to 128 3‐HB building blocks (mol. weight>11 000 Da) are assembled (Schemes 1,2,5, and6). In contrast to the previously employed protecting‐group combination, and due to the low‐temperature esterifying conditions, this procedure leads to monodisperse oligomers: all steps occur without loss of single 3‐HB units. The product oligomers with two, one, and no terminal protecting groups (mostly prepared in multi‐gram amounts) are characterized by all standard spectroscopic methods, especially by mass spectroscopy (Figs. 2and3), by their optical activity, and by elemental analyses. Cyclization of the oligo[(R)‐3‐hydroxybutanoic acids] with up to 32 3‐HB units, using thiopyridine activation and CuBr2for the ring closure, produces oligolides consisting of up to 128 ring atoms (Scheme 7). Mixed oligolides containing 3‐HB and (R)‐3‐hydroxypentanoic units are prepared from the corresponding linear trimers, usingYamaguchi's method for the ring closure (Scheme 8andFig.4(X‐ray crystal structures of two folded conformers)). Comparisons of melting points (Table 1), of [α] 36520values (Tables 2and3), of1H‐NMR coupling constants (Table 3), and of molecular volume/hydroxyalkanoate unit (Table 4) of linear and cyclic oligomer derivatives and of the high‐molecular‐weigh polymer show that the monodisperse oligomers appear to be surprisingly good models for the polymer. Besides this insight, our synthesis is supplying the samples to further test the role of P(3‐HB) (ca.140 units) as a component of complexes formi

ISSN:0018-019X    

DOI:10.1002/hlca.19960790311

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY