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.
Oxidation of Epilupinine (2). Pure 2 was oxidized as described for the oxidation of 1 with practically the same results, apart from a higher yield (40 ± 50%) of solid aldehyde. Also in this case, the GC/MS of the initially oily aldehyde indicated the presence of two fractions with M 167 in a ratio 7 ± 9 : 1.
Reduction of Prepared Aldehydes. The NaBH 4 reduction of either the oily or solid aldehydes obtained from both 1 and 2 gave always similar mixtures of 1 and 2 (TLC), with a large prevalence of the latter, similar to the reduction of 6 isolated from the epimerization mixture.