摘要:

Abstract1′,2′‐Dideoxy‐D‐ribofuranose (ab), its 5′‐ and 3′‐phosphorylated analogues (ab5 and ab3), and the DNA trimer d(Ap(ab)pA) have been studied by means of proton NMR spectroscopy. These fragments are of interest as model compounds for abasic lesions occurringin vivo. All abasic sugars exhibit similar S‐type sugar conformations with populations of S‐conformer varying from 75% (in ab and ab5) to 83% (in ab3 and dab(2)),Ps≈ 144° and Φsin the range from 30 to 33°. Having established the presence of mainly S‐type sugar, we could assign the H1′ and H1″ protons of all abasic residues stereospecifically on the basis of their respective vicinal coupling constants. The trimer exhibits considerable flexibility in the backbone. Moreover, chemical shifts as a function of temperature and chemical‐shift differences between abasic sugar protons in the trimer and in the abasic monomers point to the presence of a structure in which dab(2) is bulged out of the helix and the terminal residues stack on top of each other. Several models which fit t

ISSN:0165-0513    

DOI:10.1002/recl.19951140302

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractTertiary alcohols5and8undergo rearrangement on treatment with thionyl chloride and pyridine, yielding octahydronaphthalenes6and9, respectively. Alcohol12under similar treatment affords a mixture of tetrahydronaphthalene14and diene15, whereas alcohol22suffers no rearrangement but produces olefin23.

ISSN:0165-0513    

DOI:10.1002/recl.19951140303

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe synthesis of sulfines (thione oxides) (2, 10and17) derived from three chiral dithio esters (1, 8and16) bearing a hydrogen at the α‐carbon atom is described. The sulfine bearing an amido group at C‐α (2), does not racemize and proved to be stable over a long period. When C‐α in the sulfine (10) bears an acetoxy group the optical activity remained unchanged for a period of two months; after longer storage a rearrangement to a mixture of dithioperoxy ester12andS‐methyl ester11took place. With an alkyl group at C‐α, the sulfine17undergoes a fast racemization and rearranges slowly to a mixture ofS‐ethyl ester14, dithioperoxy ester18andS‐viny

ISSN:0165-0513    

DOI:10.1002/recl.19951140304

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe synthesis of 2‐(trifluoromethyl)piperazine (1) is reported.1H NMR spectroscopy shows that in the chair‐type piperazine ring the CF3group occupies an equatorial position. X‐ray photoelectron spectroscopy of solid 1 reveals that the CF3group induces a secondary (β) chemical shift of 1.5 eV on the C 1score binding energy of its nearest neighbour carbon atom. The results are supported by semi‐empirical PM3 and HAM/3 calc

ISSN:0165-0513    

DOI:10.1002/recl.19951140305

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractCombination of upper‐rim‐1,3‐difunctionalized calix[4]arenes14, 16, and18with tribridged resorcinarenes4and6and A,C‐di‐bridged resorcinarenes10and13yields both 1/1 calix‐resorcinarenes (22–24) and 2/1 calix‐resorcinarenes (25, 26). 1/1 Calix‐resorcinarene22mainly exists as one conformer (a), but at low temperatures (−60°C) very small amounts (<5%) of a second conformer (b) can be observed. Both conformers equilibrate via rotation about one of the C(arene)‐N bonds, with an activation free energy (ΔG≠) of 13 kcal/mol. 2/1 Calix‐resorcinarenes25and26are more flexible and exist as a mixture of conformers. In order to be able to rigidify the structure of 2/1 calix‐resorcinarenes via rigid spacers between the calix[4]arene fragments, 1,3‐diaminocalix[4]arene derivatives31, 32, and34were synthesized carrying nitro, carboxylic ester, and cyano groups at the unsubstituted aromatic rings. With these calix[4]arene derivatives, three new, functionalized 2/1 calix‐resorci

ISSN:0165-0513    

DOI:10.1002/recl.19951140306

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19951140307

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19951140309

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19951140311

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19951140301

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY