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  • 1
    Electronic Resource
    Electronic Resource
    Enantioselective Addition of Chiral Organotitanium Derivatives to Aldehydes (1981)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 64 (1981), S. 2485-2488 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Alkoxy- and aryloxy-organotitanium compounds 2-4 derived from (S)-2-methyl-1-butanol, (R)-2-butanol, (-)-menthol, quinine, cinchonine, and (S)-1.1′-binaphthol are added to aromatic aldehydes to give optically active alcohols 5-10 in enantioselectivities of up to 88% e. e., with nucleophilic transfer of methyl, phenyl, and 1-naphthyl groups. The Tables 1-3 list the effects of varying the reagents, the substrates, and the reaction conditions of the new asymmetric synthesis.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19810640755
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  • 2
    Electronic Resource
    Electronic Resource
    Selectivities in the Reactions of Alkyl-, Aryl- and Heterosubstituted Organotitanium Compounds Preliminary Communication (1981)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 64 (1981), S. 357-361 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solutions of the title compounds R-Ti(OR′)3 (1) are generally available from organolithium (or magnesium) derivatives according to equation 1. It is shown (Table 1) that some heterosubstituted organotitanium compounds are more stable thermally than their lithium counterparts. The reagents 1 are highly selective carbonylophiles (Tables 1 and 2), their reactivity can be modified by variation of the R′O-group (Table 3) and with the chiral (S)-2-methyl-l-butoxy group an enantioselective addition can be achieved [equ. 2].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19810640136
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  • 3
    Electronic Resource
    Electronic Resource
    Stability of Alkoxycarbonylamidine Prodrugs (1998)
    Springer
    Pharmaceutical research 15 (1998), S. 434-441 
    Details
    ISSN: 1573-904X
    Keywords: peptidomimetic stability ; alkoxycarbonylamidine ; ester ; prodrug ; pH-rate profile ; GPIIbIIIa
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. Alkoxycarbonylamidine prodrug modification was used to mask the positively-charged amidine moiety of an Arg-Gly-Asp pepti-domimetic and enhance oral bioavailability. The aqueous stability of ethoxycarbonylamidine (EGA), ethanethiocarbonylamidine (ETCA) and phenoxycarbonylamidine (PCA) prodrugs was examined. Methods. Degradation was followed by RP-HPLC and rate constants were determined from a degradation scheme defined by product analysis. Results. EGA gave a pH of maximum stability at pH ∼7 and was independent of pH below pH ∼4. A novel degradation pathway of EGA, conversion to ethoxycarbonyl- aminocarbonyl, was observed below pH 7. The relative rates below pH 7 were ECA~ETCA〈PCA, in the same order of decreasing pKa of the conjugate acid of the substituted amidino group. Base-catalyzed cleavage of EGA to yield the amidine derivative gave the relative rates ECA〈ETCA〈PCA, in agreement with the decreasing pKa of the leaving groups. Conclusions. The observed rate constants at all pHs were small enough that only 5-30% (depending on the substituent) undesirable degradation is predicted during transit time of the gut. The spontaneous post-absorptive conversion to the amidine drugs at neutral pH is predicted to be 6x greater for the PCA than the EGA prodrugs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1011928415808
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