Gene/Protein
Disease
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Drug
Enzyme
Compound
Pivot Concepts:
Gene/Protein
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Enzyme
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Target Concepts:
Gene/Protein
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Query: UMLS:C0847097 (
acidity
)
15,165
document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)
The synthesis of
16a
'-homo-leurosidine was achieved through enantioselective generation of a ring D'-seco-precursor 33 (without requirement of a chiral auxiliary). Its cyclization provided the N(b')-quaternary salt 35 with a configuration corresponding to the atropisomeric form 8a rather than 8b of the target product. On debenzylation, the amine 8a was obtained and found not to isomerize thermally to the anticipated atropisomer 8b (in contrast to its lower homologue, with its formation of natural leurosidine). However, on protonation, a 1:1 mixture of atropisomers of
16a
'-homo-leurosidine was obtained. A synthesis of
16a
'-homo-vinblastine provided two atropisomers 5a and 5b for the free base at equilibrium (1:2.3 at room temperature in CDCl(3)), with a shift to the major conformer 5b with increasing solvent
acidity
or decreasing temperature. The synthesis was achieved through a stereoselective inversion of the tertiary hydroxyl function in the enantioselectively generated C-20' progenitor 39.
...
PMID:The syntheses of 16a'-homo-leurosidine and 16a'-homo-vinblastine. Generation of atropisomers. 1148 50
The angucyclinones with aromatic ring B (1a-c and 2a-c) are prepared in a biomimetic-type synthesis by two successive aldol cyclizations starting from the substituted naphthoquinones 12a-c. In both cyclization steps the C-H
acidity
of the potential nucleophilic centers determines the mode of cyclization under kinetically controlled conditions. The tetrahydroanthraquinones 13a-c/14a-c are hydroxylated at C-4 to the phenolic anthraquinones
16a
-c upon treatment with excess NMO.
...
PMID:Synthesis of Angucyclines. 8. Biomimetic-Type Synthesis of Rabelomycin, Tetrangomycin, and Related Ring B Aromatic Angucyclinones. 1167 66
