Regio- and stereoselectivity in the coupling reaction of secologanin with dopamine derivatives.
The coupling reaction of tetraacetylsecologanin with dopamine and its N-benzyl derivative was investigated. In both series, stereoisomers at C-1, as well as regioisomer normal and neo compounds, were formed. Moreover, the N-unsubstituted products were partially lactamized, and the N-benzyl derivatives epimerized at C-1. In the products, the R configuration of C-1 over the S and the formation of the normal structure over the neo one predominated. The epimerization of both epimers gave an equilibrium of R and S in a ratio of 7:3 and was interpreted by cleavage of the C-1-N-2 bond. The fact that lactamization was much faster in the R than in the S series was explained on the basis of the supposed transition states. The structure, the configuration of C-1, and in several cases the conformations were established by detailed NMR studies and supported by chemical correlations.
Beke
G
G
Institute of Organic Chemistry, Semmelweis University, Högyes u. 7, H-1092 Budapest, Hungary.
Szabó
L F
LF
Podányi
B
B
D004298:Dopamine / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism*; D057888:Iridoid Glucosides; D039823:Iridoids; D007536:Isomerism; D009682:Magnetic Resonance Spectroscopy; D011714:Pyrans / Q000737:chemistry / Q000378:metabolism*
D057888:Iridoid Glucosides; D039823:Iridoids; D011714:Pyrans; C021086:secologanin; D004298:Dopamine