An improved procedure for the preparation of 8-substituted guaninesElectronic supplementary information (ESI) available: characterisation of new compounds. See http://www.rsc.org/suppdata/cc/b3/b302529b/
作者:Ming Xu、Fabio De Giacomo、Duncan E. Paterson、Tesmol G. George、Andrea Vasella
DOI:10.1039/b302529b
日期:——
The preparation of 8-substituted guanines using a new phosphorus(III)-mediated cyclisation of 4-acylamino-5-nitrosopyrimidines as the key step is described.
Reverse Turn Induced π-Facial Selectivity during Polyaniline-Supported Cobalt(II) Salen Catalyzed Aerobic Epoxidation of <i>N</i>-Cinnamoyl <scp>l</scp>-Proline Derived Peptides
作者:Jyoti Prokosh Nandy、E. N. Prabhakaran、S. Kiran Kumar、A. C. Kunwar、Javed Iqbal
DOI:10.1021/jo020352j
日期:2003.3.1
A novel chemo- and diastereoselective aerobic epoxidation of the N-cinnamoyl peptides catalyzed by polyaniline-supported cobalt(II) salen (PASCOS) is described. The N-cinnamoyl proline derived peptides 1 show a high pi-facial selectivity during these epoxidations. The origin of this diastereo-selectivity in 1 has been attributed to (i) the propensity of the N-cinnamoyl proline amide to exist predominantly as trans rotamer in CDCl3, DMSO-d(6), and CH3CN medium and (ii) existence of these peptides as organized structures (gamma- and beta-turns) due to the presence of intramolecular hydrogen bonds. An extensive solution NMR and MD simulation study on 1d and 1f indicates that the origin of the high pi-facial selectivity is due to the well-defined gamma- and beta-turns which result in the hindrance of one face of the cinnamoyl double bond in the transition state of the epoxidation reaction.