Premium
Epimerization of Lupinine to Epilupinine and vice versa. Reexamination of the Structures of Lupinal and Epilupinal
Author(s) -
Sparatore Anna,
Tasso Bruno,
Boido Vito,
Sparatore Fabio
Publication year - 2005
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.200590005
Subject(s) - chemistry , epimer , salt (chemistry) , double salt , organic chemistry , stereochemistry
Abstract Although the epimerization of lupinine ( 1 ) has been largely investigated, a previously not observed compound of formula C 10 H 17 NO was now isolated from the mixture of alkaloids that remains after the separation of epilupinine ( 2 ). It is insoluble in dry Et 2 O but soluble in EtOH, from which it is recovered as an Et 2 O‐soluble oil that slowly returns to the Et 2 O‐insoluble solid form. For these characteristics and based on GC/MS, 1 H‐NMR, and IR data, it is considered as the inner salt 6 of the common enolic form 5 of lupinal ( 3 ) and epilupinal ( 4 ), with which it is in equilibrium when standing in solution (see Scheme 1 ). The oily form, but not the solid one, is able to improve the conversion of 1 to 2 , establishing the role of the aldehydes in the epimerization process. It was observed that also 2 can be converted to 1 . Finally, the solid lupinal described by Zaboev should be considered as being identical to the now isolated inner salt 6 , while the oily epilupinal of Wicky and Schumann is, indeed, a mixture of epilupinal ( 4 ) with a minor amount of lupinal ( 3 ), which, on standing, is converted to the inner salt 6 of the common enolic form 5 .