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Träfflista för sökning "L773:0040 4020 srt2:(1995-1999)"

Sökning: L773:0040 4020 > (1995-1999)

  • Resultat 1-38 av 38
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1.
  • Olsson, Roger, et al. (författare)
  • Endocyclic cleavage of glycosides. VI. Substituent effects of the alkylative endocyclic cleavage of glycosides
  • 1998
  • Ingår i: Tetrahedron. - 0040-4020. ; 54:15, s. 3935-3954
  • Tidskriftsartikel (refereegranskat)abstract
    • A number of pentopyranoside derivatives were treated with Me 3 Al in order to investigate the influence of structural parameters on the methyl group transfer in the endocyclic alkylative cleavage reaction of these substrates. A cyclic CH ··· O hydrogen bonded model is suggested as an intermediate, which is used to explain the stereoselectivities for different substrates. In several, cases the diastereoselectivities were better than 9:1.
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  • Garg, Neeraj, et al. (författare)
  • Preparation of cis-5-methoxy-and-7-methoxy-1-acetoxy-1,2,3,4,4a,10a-hexahydro-9(10H)-phenanthrenone. An epoxide-arene reaction involving a selective 1,2-alkyl shift rearrangement
  • 1996
  • Ingår i: Tetrahedron. - 0040-4020 .- 1464-5416. ; 52:48, s. 15209-15224
  • Tidskriftsartikel (refereegranskat)abstract
    • The preparation of cis-1α-acetoxy-7-methoxy-1,2,3,4,4a,10a-hexahydro-9(10H)- phenanthrenone 5 was accomplished starting from 6-methoxy-1-tetralone. Reduction of 7-methoxy-1,2,3, 4,9,10-hexahydro-1-oxo-phenanthrene 8, acetylation and subsequent oxidation delivered 5. Application of an analogus procedure to the preparation of cis-1β-acetoxy-5-methoxy-1,2,3,4,,4a,10a-hexahydro-9(10H)- phenanthrenone 6 was not feasible. A more elaborate route was developed for the synthesis of compound 6, where an epoxide-arene reaction involving a 1,2-alkyl shift rearrangement, constituted a highly selective key transformation. The compounds 5 and 6 were prepared. A route was developed for the synthesis of compound 6, where an epoxide-arene reaction involving a 1,2-alkyl shift rearrangement, constituted a highly selective key transformation.
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  • Kuhn, Christian, et al. (författare)
  • Fmoc protected peptide mimetic based on a cyclohexane framework and incorporation into angiotensin II
  • 1997
  • Ingår i: Tetrahedron. - 0040-4020 .- 1464-5416. ; 53:37, s. 12497-12504
  • Tidskriftsartikel (refereegranskat)abstract
    • 1,3,5-syn substituted cyclohexane based amino acids have been prepared and incorporated into synthetic peptides to serve as scaffold mimicking the Val-Tyr-Ile sequence of angiotensin II. The conformationally constrained tripeptide mimetic holds potential use as a γ-turn replacement.
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  • Laglet, Abraham, et al. (författare)
  • Synthesis and Reactions of 1,1-dinitro-2,2-dinitroethylene
  • 1998
  • Ingår i: Tetrahedron. - 0040-4020 .- 1464-5416. ; 54:38, s. 11525-11536
  • Tidskriftsartikel (refereegranskat)abstract
    • Low temperature nitrations of 2-methylimidazole gave in addition to the known 2-methyl-5(4)-nitroimidazole (1), 2-(dinitromethylene)-5,5-dinitro-4-imidazolidinone (3) and parabanic acid (2). The tetranitro compound 3 was also obtained by nitration of 2-methyl-4,5-dihydro-(1H)-5-imidazolone (8). Thermal decomposition of 3 gave 2-(dinitromethylene)-4,5-imidazolidinedione (4) which also was the product from nitration of the new compound 2-methoxy-2-methyl-4,5-imidazolidinedione. Treatment of 4 with aqueous ammonia gave the previously unknown 1,1-diamino-2,2-dinitroethylene (5). The physical properties and chemical behaviour of (5) are described.
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  • Marton, J., et al. (författare)
  • Reaction of morphinan-6,8-dienes with azadienophiles
  • 1996
  • Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020 .- 1464-5416. ; 52:7, s. 2449-2464
  • Tidskriftsartikel (refereegranskat)abstract
    • Reaction of various morphinan dienes, i.e. thebaine (1a), N-demethyl-N-formylthebaine (1b), 6-demethoxythebaine (1c), β-dihydrothebaine (2a), 4-acetoxy-β-dihydrothebaine (2b), 7-chloro-6-demethoxythebaine (3a) and 7-bromo-6-demethyoxythebaine (3b) with 4-phenyl-4H-1,2,4-triazoline-3,5-dione (PTAD) gave rise to new Diels-Alder (DA) adducts. DA-reaction of 1a, 1b and 1c with PTAD led to the products of the β-face attack of the dienophile at the diene unit. The W coupling (4J(5β,18)) in the 1H-NMR spectra was indicative of these structures. α-Face addition took place in the case of morphinan dienes with opened ring E, and a by-product was formed due to the S(E) reaction of PTAD with the adducts. The structure of these derivatives was confirmed by means of NMR spectroscopic methods. The retro Diels-Alder (rDA) reaction of the adducts 4a and 4b readily took place in polar-aprotic solvents in the presence of bases with low nucleophilic character.
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  • Marton, J., et al. (författare)
  • Studies on the synthesis of β-thevinone derivatives
  • 1998
  • Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020 .- 1464-5416. ; 54:31, s. 9143-9152
  • Tidskriftsartikel (refereegranskat)abstract
    • The reactions of β-thevinone and β-dihydrothevinone with tert- butylmagnesium chloride and n-propylmagnesium bromide were investigated. Further chemical transformations (N-demethylation, N-alkylation, O- demethylation) of the tertiary alcohols afforded the known β-buprenorphine and the hitherto unknown β-etorphine and β-dihydroetorphine. The by- products of these reactions were also isolated, their structures identified, and the mode of their formation was explained.
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  • Luyten, I, et al. (författare)
  • Determination of the ionization constants of C-nucleosides
  • 1997
  • Ingår i: TETRAHEDRON. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0040-4020. ; 53:20, s. 6903-6906
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • We here report for the first time the ionization constant of 9-deazaadenosine (1) (pK(a) 6.0) as well as the third ionization constant for Formycin B (2) (pK(a) of 1.3) in addition to its two known pK(a)s of 8.8 and 10.4. (C) 1997 Elsevier Science Ltd.
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  • PAPCHIKHIN, A, et al. (författare)
  • THE DIASTEREOSPECIFIC SYNTHESIS OF NEW 2',3'-CIS-ALPHA-FUSED CARBOCYCLIC NUCLEOSIDES
  • 1995
  • Ingår i: TETRAHEDRON. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0040-4020. ; 51:1, s. 329-342
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The first diastereospecific synthesis of [3.3.0]- and [3.4.0]-alpha-cis-fused-carbocyclic nucleosides 10, 12 and 20, starting directly from 2'-O-(TBDMS) or 3'-O-(TBDMS) derivatives of 5'-O-MMTr-2',3'-seco-ribo-thymidines, 1 and 13 (ref. 4), have been repo
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  • Trifonova, A, et al. (författare)
  • Diastereospecific chemical synthesis of ribonucleosides-3 ',4 ',5 ',5 ''-d(4)
  • 1999
  • Ingår i: TETRAHEDRON. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0040-4020. ; 55:15, s. 4747-4762
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The diastereospecific chemical syntheses of uridine-3',4',5',5"-d(4), cylidine-3',4',5',5''-d(4), adenosine-3',4',5',5"-d4 and guanosine-3',4',5',5"-d(4) (>97 atom % H-2 at C3', C4' and C5') have been achieved by condensation of appropriately protected ag
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  • Resultat 1-38 av 38

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