摘要:

AbstractThe synthesis ofC‐glycosidic analogues15–22ofN4‐(2‐acetamido‐2‐deoxy‐β‐D‐glucopyranosyl)‐L‐asparagine (Asn(N4GlcNAc)) possessing a reversed amide bond as an isosteric replacement of theN‐glycosidic linkage is presented. The peptide cyclo(‐D‐Pro‐Phe‐Ala‐CGaa‐Phe‐Phe‐) (CGaa =C‐glycosylated amino acid;24) was prepared to demonstrate that 3‐[(3‐acetamido‐2,6‐anhydro‐4,5,7‐tri‐O‐benzyl‐3‐deoxy‐β‐D‐glycero‐D‐guloheptonoyl)amino]‐2‐[(9H‐fluoren‐9‐yloxycarbonyl)amino]propanoic acid (22) can be used in solid‐phase peptide synthesis. The conformation of24was determined by NMR and molecular‐dynamics (MD) techniques. Evidence is provided that the CGaa side chain interacts with the peptide backbone. The differentC‐glycosylated amino acids15–21were prepared by coupling 3‐acetamido‐2,6‐anhydro‐4,5,7‐tri‐O‐benzyl‐3‐deoxy‐β‐D‐glycero‐D‐gulo‐heptonic acid (4) with diamino‐acid derivatives8–14in 83–96% yield. The synthesis of4was performed from 2‐(acetamido‐3,4,6‐tri‐O‐benzyl‐2‐deoxy‐β‐D‐glucopyranosyl) tributylstannane (2) by treatment with BuLi and CO2in 83% yield. Similarly, propyl isocyanat yielded the glycoheptonamide7in 52% from2. Compound2was obtained from 2‐acetamido‐3,4,6‐tri‐

ISSN:0018-019X    

DOI:10.1002/hlca.19960790602

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractCyclohexa‐1,3‐dienes7–10with a 1,5,6‐substitution pattern were prepared in a one‐pot reaction sequence by sequential addition of MeLi and propargyl bromides to the tricarbonylchromium complex1a. These products were subjected to radical cyclization procedures. Vinyl radical generation by Bu3Sn addition to the propargyl group in7–10was followed by regio‐ and diastereoselective intramolecular ring closure. Two different 5‐exo‐trigcyclizations are possibleviadifferent vinyl radical intermediates and cyclization to one or the other of the termini of the cyclohexadiene moiety. Internal alkynes reacted to yield exclusively thecis‐fused hexahydroindene products12–14, whereas the terminal alkyne yielded bicyclo[3.2.1]octe

ISSN:0018-019X    

DOI:10.1002/hlca.19960790603

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

Synthesis of Trifluoromethyl‐Substituted Sulfur Heterocycles Using 3,3,3‐Trifluoropyruvic‐Acid DerivativesThe reaction of methyl 3,3,3‐trifluoropyruvate (1) with 2,5‐dihydro‐1,3,4‐thiadiazoles4a, bin benzene at 45° yielded the corresponding methyl 5‐(trifluoromethyl)‐1,3‐oxathiolane‐5‐carboxylates5a, b(Scheme 1)viaa regioselective 1,3‐dipolar cycloaddition of an intermediate ‘thiocarbonyl ylide’ of type3. With methyl pyruvate,4areacted similarly to give6in good yield. Methyl 2‐diazo‐3,3,3‐trifluoropropanoate (2) and thiobenzophenone (7a) in toluene underwent a reaction at 50°; the only product detected in the reaction mixture was thiirane8a(Scheme 2). With the less reactive thiocarbonyl compounds 9H‐xanthene‐9‐thione (7b) and 9H‐thioxanthene‐9‐thione (7c) as well as with 1,3‐thiazole‐5(4H)‐thione12, diazo compound2reacted only in the presence of catalytic amounts of Rh2(OAc)4. In the cases of7aand7b, thiiranes8band8c, respectively, were the sole products (Scheme 3). The crystal struture of8chas been established by X‐ray crystallography (Fig.). In the reaction with12, desulfurization of the primarily formed thiirane14gave the methyl 3,3,3‐trifluoro‐2‐(4,5‐dihydro‐1,3‐thiazol‐5‐ylidene)propanoates (E)‐and (Z)‐15(Scheme 4). A mechanism of the Rh‐catalyzed

ISSN:0018-019X    

DOI:10.1002/hlca.19960790604

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractThe oligonucleotide building blocks, the phosphonates1a, band the phosphoramidites2a, bderived from 7‐iodo‐ and 7‐bromo‐7‐deaza‐2′‐deoxyguanosines3a, bwere prepared. They were employed in solid‐phase oligonucleotide synthesis of the alternating octamers d(Br7c7G‐C)4(8) and d(I7c7G‐C)4(9) as well as the homo‐oligonucleotides d[(Br7c7G)5‐G] (11) and d[(I7c7G)5‐G] (12). The melting profiles and CD spectra of oligonucleotide duplexes were measured. TheTmvalues as well as the thermodynamic data were determined and correlated to the major‐groove modification of this DNA. The self‐complementary octamers8and9form more stable duplexes compared to the parent oligomer d(G‐C)4. The heteroduplex of d[(I7c7G)5‐G] (12) with d(C6) is slightly destabilized (ΔTm= −12°) over that of d[(c7G)5‐G] with d(C6). However, the complex of12with poly(C) is more sta

ISSN:0018-019X    

DOI:10.1002/hlca.19960790605

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractThe intense sweet and coconut‐like smelling odorant1, named ‘wine lactone’, was isolated from different wine varieties. The chemical structure of this compound, which has not yet been detected in wine or a food, was identified by high‐resolution mass spectrometry (HR‐MS) as 3a,4,5,7a‐tetrahydro‐3,6‐dimethylbenzofuran‐2(3H)‐one. For the evaluation of the configuration of wine lactone, stereochemically controlled syntheses were developed. All eight isomers were characterized by NMR, MS, IR, and CD measurements. The configuration of ‘wine lactone’ was in agreement with synthesized (3S,3aS,7aR)‐enantiomer (1a) on the basis of enantioselective GC. For this isomer, the lowest odor threshold (0.

ISSN:0018-019X    

DOI:10.1002/hlca.19960790606

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

Steroselective Synthesis of the Nitrite‐Reducing Cofactor Heme d1from HematoporphyrinThe nitrite‐reducing cofactor heme d1has been synthesized in a few synthetic steps, starting from readily accessible hematoporphrin dimethyl ester (rac‐4a). A single‐crystal structure analysis of the synthesized target moleculerac‐10aunequivocally established the constitution and the relative configuration of h

ISSN:0018-019X    

DOI:10.1002/hlca.19960790607

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractThe ligand (6,6′‐dimethoxybiphenyl‐2,2′‐diyl)bis[3,5‐di(tert‐butyl)phenylphosphine] (1) forms an unexpectedly stable hydrido‐bis‐solvento complex of composition [RuH(isopropanol)2(1)]BF4, (2) under the conditions used in the enantioselective hydrogenation of pyrones. The structure of2, determined by X‐ray diffraction, represents the first well‐characterized chiral five‐coordinate bis‐phosphine ruthenium‐hydride complex stable as a solvento complex, and provides a structural link in the enantioselective pyrone hydrogenation cycle catalyzed by [Ru(OAc)2(1)]. Using the arene complex [RuH(p‐cymene)(1)]BF4(3), the chiral pocket of coordinated1is shown to be relatively rigid,viaNMR spectroscopy. This is reflected in restricted rotation about one of the fourP–[3,5‐di(tert‐butyl)phen

ISSN:0018-019X    

DOI:10.1002/hlca.19960790608

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

Acid‐Catalyzed Rearrangement of 9‐Hydroxyfuranoeremophilanes to Eremophilanlactones9‐Hydroxyfuranoeremophilanes1–3are the main components of freshly harvested rhizomes ofP. hybridus(furanopetasin chemovar, Table, Fig. 1). They easily and quantitatively rearrange in the presence of traces of acid to give an epimeric mixture of 8‐H‐eremophilanlactones4–6(eremophilenolides,Table, Figs. 4and5). Besides subsequent oxidation (see4→7), this is the most important reaction occuring during drying and storage of rhizomes ofP. hybridus(Figs. 1and3). A reasonable mechanism of the rearrangement is presented, and spectroscopic structure elucidation of 8‐H‐eremophilanla

ISSN:0018-019X    

DOI:10.1002/hlca.19960790609

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractThe molecular structure of the two complex ions [Co(tmen)3]3+and [Co(tmen)3]2+(tmen = 2,3‐dimethylbutane‐2,3‐diamine) have been determined at 100 K. They show a strong trigonal distortion of the octahedral CoN6core. The twist angle is 26.2(2.8)° for CoIIand 43.9(9)° for CoIII. Average CoN distances are 2.193(13) Å (CoII) and 1.997(2) Å (CoIII), 0.02 Å longer than for the main body of

ISSN:0018-019X    

DOI:10.1002/hlca.19960790610

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractGlycosylrifamycins, a new type of semisynthetic rifamycin derivatives, can be easily obtained by reaction of 3‐(2‐aminoethylthio)rifamycin SV (2) with a glycosyl compound carrying a coupling group, such as isothicyanate or carboxy. We preparedO‐acetylated and free glucopyranosyl and arabinopyranosyl derivatives of rifamycin S and SV (see3–10). Additionally, derivatives withD‐saccharo‐1,4‐lactone and with shikimic acid were obtained (see11–15). Glycosylrifamycins show an interesting inhibitory power onGram‐positive

ISSN:0018-019X    

DOI:10.1002/hlca.19960790611

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY