Ring cleavage directed

Ring cleavage of l-oxo-l,2,3,4-tetrahydro-jS-carboline derivatives (374) may be accomplished by base-catalyzed hydrolysis to yield tryptamine-2-carboxylic acids (375). In the case of the 1,9-dimethyl derivative decarboxylation accompanied acid-catalyzed ring-opening, and the corresponding tryptamine (376) was obtained directly. 

Fischer, F., and Fetzner, S., Site-Directed Mutagenesis of Potential Catalytic Residues in lh-3-Hydroxy-4-Oxoquinoline 2, 4-Dioxygenase, and Hypothesis on the Catalytic Mechanism of 2, 4-Dioxygenolytic Ring Cleavage. FEMS Microbiol Lett, 2000. 190 pp. 21-27. 

Thiadiazole 1,1-dioxides are known they are not prepared by direct oxidation of the 1,2,4-thiadiazole ring, as ring cleavage occurs giving sulfate ion. They are only accessible by cyclization of precursors already incorporating the oxidized sulfur functions <1996CHEC-II(4)307>. 

A-Boc-A -isopropylimidazolidine (175) is deprotonated by the (—)-sparteine method and alkylated to form imidazolidines 176 (equation 41). The yields remain below 50%, since only a part of 175 exists in the shown conformation, which is required for the directed deprotonation. At low temperature, the interconversion between the s-trans- and i-c -conformation is too slow. Ring cleavage furnishes synthetically useful chiral 1,2-diamines 177. 

Attempts to bring about a direct reversal of the ring cleavage of the trimetaphosphate have so far been unsuccessful. However, ring closure was effected, though through a series of intermediate substances, by treating... 

Condensations of ammonia and methylamine with 1-alkyll. 1 -epoxycycloalkanea were likewise examined thoroughly by Mouseeron and Granger i to test the directive effect of alkyl substituents on the sense of ring opening. In every instance ring cleavage followed I hr... 

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