摘要:

AbstractTwo newC2chiral bidentate phosphorous ligands have been prepared in enantiomerically pure form. The two phosphorous centers bear electron‐withdrawing groups ((CF3)2CHO, C6F5) and are linked by atrans‐cyclopentane‐1,2‐diol‐derived bridge. Photolysis of [Cr(η6‐C6H6)(CO)3] in the presence of these two new ligands and of two previously reported bidentate phosphites, and fluorophosphinites (L) afforded [Cr(η6‐C6H6)(CO)L] complexes. IR Spectral comparison of the complexes shows the new ligands to be intermediate in their bonding properties between alkyl

ISSN:0018-019X    

DOI:10.1002/hlca.19940770202

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractFrom guanosine (1) as starting molecule, protected arabinoguanosine derivatives such as phosphoramidite precursors and arabinoguanosine (18) itself were prepared in high yields. Inversion of the configuration at C(2′) was achieved by introduction of the (trifluoromethyl)sulfonyl residue and subsequent displacement by nucleophiles like acetate, bromide, and azide. The guanine moiety was protected at the amide function by the 2‐(4‐nitrophenyl)ethyl (npe) group on O6and at the NH2function by the 2‐(4‐nitrophenyl)ethoxycarbonyl (npe

ISSN:0018-019X    

DOI:10.1002/hlca.19940770203

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

Reaction of Di(tert‐butyl)‐ and Diphenyldiazomethane and 1,3‐Thiazole‐5(4H)‐thiones: Isolation and Crystal Structure of the Primary CycloadductReactions of diazo compounds with CS bonds proceedviathe formation of thiocarbonyl ylides, which, under the reaction conditions, undergo either 1,3‐dipolar cycloadditions or electrocyclic ring closer to thiiranes (Scheme 1). With the sterically hindered di(tert‐butyl)diazomethane (2c), 1,3‐thiazole‐5(4H)‐thiones1react to give spirocyclic 2,5‐dihydro‐1,3,4‐thiadiazoles3(Scheme 2). These adducts are stable in solution at −20°, and they could be isolated in crystalline form. The structure of3cwas established by X‐ray crystallography. In CDCl3solution at room temperature, a cycloreversion occurs, and the adducts of type3are in an equilibrium with1and2c. In contrast, the reaction of1with diphenyldiazomethane (2d) gave spirocyclic thiiranes4as the only product in high yield (Scheme 3). The crystal structure of4bwas also determined by X‐ray analysis. The desulfurization of compounds4to 4,5‐dihydro‐5‐(diphenylmethylidene)‐1,3‐thiazoles5was achieved by treating4with triphenylphosphine in boi

ISSN:0018-019X    

DOI:10.1002/hlca.19940770204

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractThe optically active urobilin model compound7was synthesized, in which Me groups instead of H‐atoms are bound to the asymmetric centers, thus preventing loss of chirality by tautomerization. The key intermediate of the eleven‐step synthesis of7is the 1,4,5,10‐tetrahydro‐10‐hydroxy‐1‐oxo‐11H‐dipyrrin‐9‐carboxylaterac‐2, which could be resolved into enantiomers by fractional crystallization of the corresponding methylN‐[1‐(naphth‐1‐yl)ethyl]carbamates3and4. The absolute configuration of enantiomerically pure (−)‐2was determined by X‐ray diffraction analysis of its camphor‐10‐sulfonate5. As the CD spectrum of the urobilin analogue7obtained from (−)‐(R)‐2displays a positiveCottoneffect, the present results prove, in connection with previous work, that substitution of Me groups for the H‐atoms bound to the asymmetric centers of a chiral urobilin chromophore do not influence the relationship between abso

ISSN:0018-019X    

DOI:10.1002/hlca.19940770205

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

4,4‐Disubstituted Imidazole Derivatives from the Reaction of 3‐Amino‐2H‐azirines with SalicylamideReaction of 3‐amino‐2H‐azirines1a–cwith salicylamide (7) in MeCN leads to imidazoles10and11in different rates, depending on the conditions. In the case of1aand1b, 11aand11b, respectively, have been obtained as the main product at 50°; in reactions at 80°,10aand10bare the favored products (Tables 1and2). 2,2‐Dimethyl‐3‐(N‐methyl‐N‐phenylamino)‐2H‐azirine (1c) reacts with7in MeCN mainly to 2‐(2‐hydroxyphenyl)‐5,5‐dimethyl‐3,5‐dihydroimidazol‐4‐one (10a); in boiling toluene,11cis formed with low preference (Table 3). The structure of the products has been established by spectroscopic means, and in the case of10band11c, by X‐ray crystallography. Two different reaction mechanisms for the

ISSN:0018-019X    

DOI:10.1002/hlca.19940770206

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractPeptide mimetics of thyrotropin‐releasing hormone (TRH) in which the peptide backbone is replaced by cyclohexane were synthesized from the cyclohexenone precursor7. The aromatic side chains of the mimetics were derived from the corresponding aldehydes which were attached to the cyclohexenoneviatheWittigreagent8. The TRH mimetics are active in a mouse model of cognitive performanc

ISSN:0018-019X    

DOI:10.1002/hlca.19940770207

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

Stereoselective Syntheses of (Z)‐(10‐Methoxy‐4H‐benzo[4,5]cyclohepta[1,2‐b]thiophen‐4‐ylidene)acetic AcidTwo stereoselective syntheses for the antiinflammatory compound1((Z)‐isomer) are described. In the first approach (Strategy A, Scheme 1) the stereoselective synthesis of1was realizedviathe bicyclic compound11under thermodynamic conditions, followed by a thiophene annelation with retention of the double‐bond geometry (Schemes 2–4). Optimized conditions were necessary to avoid (E/Z)‐isomerization during annelation. In the second approach (Strategy B, Scheme 1), diastereoisomer17bwas obtained selectively from a mixture of the diastereoisomers17band18bby combining thermodynamic epimerization and solubility differences (Scheme 5). Diastereoisomer17bwas converted into the tricyclic compound23using a novel thiophene annelation method which we described recently (Scheme 6). In a final step, a stereospecific ‘syn’‐elimination transformed the sulfoxide24into the target compound1(Scheme 7). To avoid (E/Z)‐isomerization, it was necessary to trap the sulfenic acid liberated during the reaction. The key reactions of both approaches are h

ISSN:0018-019X    

DOI:10.1002/hlca.19940770208

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractThe 2‐dansylethoxycarbonyl (Dnseoc) group was employed for protection of the 5′‐hydroxy function in oligoribonucleotide synthesis by the phosphoramidite approach using the acid‐labile tetrahydro‐4‐methoxy‐2H‐pyran‐4‐yl (Thmp) group for 2′‐protection. The syntheses of monomeric building blocks, both phosphoramidites and nucleoside‐functionalized supports, are described for the four common nucleosides adenosine, guanosine, cytidine, and uridine, and for the two modified minor nucleosides ribothymidine (= ribosylt

ISSN:0018-019X    

DOI:10.1002/hlca.19940770209

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractA series of insect juvenile hormone analogs (juvenoids) was synthesized and studied. The basic skeleton of these juvenoids contains three rings and a short aliphatic subunit and bears two or three chiral centers (depending on the appropriate structure; see6–9). The chiral center located in the 1,2‐diphenoxypropane subunit has the configuration (RS), (R) (aseries), or (S) (bseries). The juvenoids were subjected to a biological screening, the preliminary results of which are briefly descri

ISSN:0018-019X    

DOI:10.1002/hlca.19940770210

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractThe synthesis of the trisaccharide α‐L‐Fucp‐(1 → 2)‐β‐D‐Galp‐(1 → 3)‐β‐D‐GalpNAc‐1‐OPr (2) is described. TheN‐acetylgalactosamine6was obtained from4by an intramolecular displacement of a (trifluoromethyl)sulfonyloxy by a pivaloyloxy group with its concomitant migration from position 3 to position 4 (Scheme 1). The galactosyl donor9was obtained from7via8by regioselective opening of the orthoester function with AcOH/pyridine followed by treatment with CCl3CN and 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) (Scheme 2). Glycosylation of6with9in the presence of BF3· OEt2gave the disaccharide10. Selective deprotection of10atOC(2′) followed by glycosylation with12and by standard deprotection afforded the title trisaccharide2(Scheme 3). Preliminary biological testing showed that2is able to inhibit the binding of the monoclonal antibody MBrl to the target

ISSN:0018-019X    

DOI:10.1002/hlca.19940770211

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY