摘要:

AbstractThe synthesis of oligonucleotides containing 2′‐deoxy‐5‐methylisocytidine and 2′‐deoxyisoguanosine using phosphoramidite chemistry in solid‐phase oligonucleotide synthesis is described. Supporting previous observations, theN,N‐diisobutylformamidine moiety was found to be a far superior protecting group thanN‐benzoyl for 2′‐deoxy‐5‐methylisocytidine. 2′‐Deoxy‐N2‐[(diisobutylamino)methylidene]‐5′‐(4,4′‐dimethoxytityl)‐5‐methylisocytidine 3′‐(2‐cyanoethyl diisopropylphosphoramidite) (1c) incorporated multiple consecutive residues during a standard automated synthesis protocol with a coupling efficiency>99% according to dimethoxytrityl release. Extending coupling times of the standard protocol to ≥ 600s using 2′‐deoxy‐N6‐[(diisobutylamino)methylidene]‐5′‐O‐(dimethoxytrityl)‐O2‐(diphenylcarbamoyl)isoguanosine, 3′‐(2‐cyanoethyl diisopropylphosphoramidite) (7e) led to successful incorporation of multiple consecutive 2′‐deoxyi

ISSN:0018-019X    

DOI:10.1002/hlca.19980810502

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractThe insecticidal polyether antibiotic X‐206 (1) complexes potassium ions using nearly all of its O‐atoms either for binding to the metal ion or for participation in a H‐bonding network which helps to hold X‐206 in the ionophoric tertiary structure. The group OHC(22) is not involved in these processes. It was supposed that derivatization of this group would not affect the ionophoric properties and would produce insecticidally active compounds. The chemistry leading to selective modification of OHC(22)viathe intermediate6was developed. The potassium‐binding properties and insecticidal activities of the MeCOOC(22) and MeOC(22) compounds3and11, respectively, confirmed that derivatization of the peripheral OHC(22) was a valid strategy for the synthesis of biological

ISSN:0018-019X    

DOI:10.1002/hlca.19980810503

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractThe [4 + 2] cycloadduct17of 2,3‐dimethylidene‐1,2,3,4‐tetrahydro‐1,4‐methanonaphthalene and 4‐phenyl‐4H‐1,2,4‐triazole‐3,5‐dione (PTAD) was subjected to a triplet‐sensitized di‐π‐methane rearrangement. Hydrolysis of the resulting urazol18gave the hydrocarbon7. Hydrolysis of18at lower base concentrations led to isomeric stable semicarbazides24and25, which were submitted NiO2or MnO2oxidation, to give the target compound7, a

ISSN:0018-019X    

DOI:10.1002/hlca.19980810504

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractThe kinetics of the reaction between pyridoxal 5′‐phosphate (PLP) with carbidopa, hydralazine, and isoniazid, in aqueous solution at variable pH and constant ionic strength of 0.1Mwas studied spectrophotometrically. The rate constants of formation and hydrolysis of the resultingSchiffbase, and its stability were determined in a wide range of pH. A comparison is made of the formation rate constants with those of PLP with hydrazine. The reactivity shows the sequence isoniazid>hydrazine>carbidopa>hydralazine in the whole range of pH studied. TheSchiffbases studied are more stable than those formed by PLP and hexylamine and as stable as those described for the reactions of PLP with poly(L‐lysine) or copolypeptides containingL

ISSN:0018-019X    

DOI:10.1002/hlca.19980810505

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractStudies towards the synthesis of a chiral primary α‐phosphinoalkanamine1aare reported.O‐Activated.N‐carbamate‐protected phenylalaninol3adid not undergoSNreaction with KPPh2: instead, afterN‐deprotonation, intramolecular substitution led to formation of the aziridine derivative5a(Scheme 2).N‐Phthalimido‐protected,O‐activated phenylalaninol3balso underwent an intramolecular process on treatment with KPPh2,i.e., an unusual aryl‐acyliminium cyclization furnishing the (epoxymethano)isoindolo[1,2‐a]isoquinolinone7(Scheme 3). In a reaction with KPPh2, theN,N‐dibenzyl‐protected and activated phenylalaninol3dfinally yielded the intermolecularSNreaction product2a(Scheme 4). However, debenzylation by catalytic hydrogenation tur

ISSN:0018-019X    

DOI:10.1002/hlca.19980810506

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractThe difference between the strong inhibition of retaining β‐glucosidases by the tetrazole1and the weak inhibition by the triazole3has been explained by the protonation by the enzymic catalytic acid of N(3) of1, replaced by CH in3. One also expects a contribution to the inhibition from the charge‐dipole interaction between the enzymic catalytic nucleophile and the azole ring. The extent of this contribution was estimated from the calculated, distance‐dependent heats of formation of the acetate‐azole complexes. The calculations were validated by comparison of the charge‐dipole interaction between phosphate and the inhibitors1and3in the glycogen phosphorylaseb(GPb)‐azole‐phosphate complexes, as derived from differences in theKivalues for1and3, while the structural invariance of the complexes was demonstrated by X‐ray analysis. The difference between the charge‐dipole interactions of (dihydrogen) phosphate and1or3as derived from ΔKiis 1.1 kcal mol−1, while the calculated difference is 1.3 kcal mol−1. The calculated difference for the interaction of1or3with acetate, representing the catalytic nucleophile in β‐glycosidases, is 2.0 kcal mol−1, while the differences of the binding energies as derived from theKivalues for the inhibition by1or3of different β‐glycosidases range from 2.4 to 5.3 5 kcal mol−1. The calculated difference for1and the imidazole6is 2.5 kcal mol−1in favour of1, whereas theKi‐derived difference is 3.7 kcal mol−1in favour of6, equal to the calculated difference between1and the protonated imidazole6. Thus, protonation by the catalytic acid and the charge‐dipole interaction with the catalytic nucleophile contribute cooperatively to the binding of inhibitors possessing a trigon

ISSN:0018-019X    

DOI:10.1002/hlca.19980810507

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractThe lactam21was obtained in an overall yield of 72% from the hydroxy amide16by oxidation with theDess‐Martinperiodinane, acid‐catalysed isomerization of the oxidation products in toluene, whereupon18/19precipitated, and reductive dehydroxylation of18/19(Et3SiH/BF3· OEt2;Scheme 1). The amide16was obtained by ammonolysis of theN‐acetylglucosamine‐derived lactone15. Depending on the oxidation method,16yielded the keto amide17, the hydroxy lactams18/19, and the pyrrolidinecarboxamide20in widely different proportions. The pyrrolidinecarboxamide20was not reduced under the conditions of the reductive dehydroxylation. Hydrogenolysis of the benzyl‐protected lactam21gave the trihydroxy lactam22, while reduction with NaBH4/BF3· OEt2led to the 2‐acetamidopiperidine derivative24(Scheme 2). Selective (tert‐butoxy)carbonylation of the lactam21(→25) followed by NaBH4reduction and acid‐catalysed solvolysis in EtOH led to the α‐ethoxycarbamates28/29. Similarly, (tert‐butoxy) carbonylation of1(→31) followed by reduction to32/33and glycosidation yielded the ethoxycarbamate34. Treatment of the GlcNAc‐derived ethyl glycosides28/29with Me3SiCN/BF3· OEt2gave the equatorial amino nitrile30. Under similar conditions, the Glc‐derived glycoside34led to the iminooxazolidinone35. In the presence of a larger proportion of Me3SiCN at 5°,34was transformed into the axial, selectively

ISSN:0018-019X    

DOI:10.1002/hlca.19980810508

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractSelective NMR decoupling and nuclearOverhausereffect (NOE) experiments with phycocyanobilin (PCB) show proton‐proton interactions between the terminal rings A and D,viz. the chiral C(2) methine center and the ethyl substituent at C(18), as a result of the helical conformation of this open‐chain tetrapyrrole in solution. Quantitative NOE measurements and a combination of force‐field and semiempirical calculations (FSC) afford inter‐proton distances across the helical gap of 4.2–4.6 (NOE) and 3.2–4.2 A° (FSC). The NOE and FSC, in conjuction with a qualitative evaluation of the steric interactions in the two optimized helices, suggest furthermore that, in solution, the helixMis somewhat more stable thanP. The coexistence of at least two diastereoisomers is corroborated also by the circular dichroism (CD) spectra of PCB in MeOH/EtOH which point to a temperature‐dependent equilibrium in solution, and by a considerable increase of this CD upon changing the solvent from the achiral alcohols to ethyl (−)‐(S)‐lactate which reflects a selective solvent‐induced CD differentiating be

ISSN:0018-019X    

DOI:10.1002/hlca.19980810509

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractThe reaction of 2‐(trimethylsilyl)thiazole (2‐TST) with several ketones was tested in the presence or absence of aldehydes. The keto aldehyde5(Scheme 2) was prepared from1viathe hydroxy aldehyde4in 3 steps. It reacted with 2‐TST to give, after desilylation and acetylation, the bis‐thiazole6. The ketone11, obtained from4in 3 steps, reacted with 2‐TST to give, after desilylation,12. The ketofuranose17(Scheme 3) reacted with 2‐TST to yield exclusively the more stableD‐glucoepimer18. The reaction of the ketone11(Scheme 2) with 2‐TST was faster in the presence of 1 equiv. of the keto aldehyde5, suggesting that an aldehyde promotes the indirect and intermolecular addition of 2‐TST to a ketone. We have studied the effect of several aldehydes on the rate of the reaction of the ketones11and17with 2‐TST at different temperatures and at different concentrations of the ketones and of the aldehydes. Electrophilic aldehydes, and particularly 2‐fluorobenzaldehyde (0.1 equiv.), promote the addition of 2‐TST t

ISSN:0018-019X    

DOI:10.1002/hlca.19980810510

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractDescribed are the preparation of nanocrystals and the synthesis of molecules that may be covalently or noncovalently assembled in solution to yield heterosupermolecules possessing a well‐defined heterosupramolecular function. Also described are preparative and synthetic methods that yield organized assemblies of heterosupermolecules possessing an addressable heterosupramolecular function. Finally, the development of these synthetic strategies to permit the covalent and noncovalent assembly and organization of a wide range of condensed phase and molecular components is outline

ISSN:0018-019X    

DOI:10.1002/hlca.19980810511

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY