ChemInform Abstract: FURTHER STUDIES ON THE CHEMISTRY AND STRUCTURE OF N‐OXIDES OF SPARTEINE AND ITS DERIVATIVES PART 4, SYNTHESIS AND STRUCTURE OF A NEW SPARTEIN‐N(16)‐OXIDE, CONFORMATION OF SPARTEINE‐N(1)‐OXIDE, CONFORMATION OF SPARTEINE‐N(1)‐OXIDE

Abstract

Durch Li‐alanat‐Reduktion des Lupanin‐N‐oxids (I) wird ein ein neues Spartein‐N‐1 6‐ oxid (II) [im 1:1‐Gemisch mit Spartein (III)] gewonnen; Na‐boranat‐Reduktion von (I) führt zu einem 85:15‐Gemisch von (II) mit einem (III)/Lupanin (IV)‐Gemisch.

NMR Spectra of Sparteine N1-oxide and α-Isosparteine N-oxide

“…Sparteine N1-oxide ( 1 ) was prepared by oxidation with 30% aqueous H 2 O 2 in methanol of the alkaloid freed from commercial (–)-sparteine sulphate pentahydrate (Aldrich), according to a previously described method [ 20 ].…”

“…The two conformers of sparteine form three isomeric mono N-oxides: sparteine N1-oxide ( 1 ), sparteine N16-oxide ( 2 ) and sparteine epi-N-oxide ( 3 ). In the reactions of sparteine with H 2 O 2 a 1:3 mixture of the two sparteine N-oxides: sparteine N 1 -oxide and sparteine N16-oxide is obtained [ 19 , 20 ]. Sparteine N1-oxide ( 1 ) occurs in a chair-boat type equilibrium involving inversion of the lone pair on the N16 atom [ 20 ]; the N16-oxide of sparteine ( 2 ), previously thought to adopt the all chair conformation, has been found recently to have ring C in a boat conformation and a cis C/D ring junction [ 21 ].…”

“…In the reactions of sparteine with H 2 O 2 a 1:3 mixture of the two sparteine N-oxides: sparteine N 1 -oxide and sparteine N16-oxide is obtained [ 19 , 20 ]. Sparteine N1-oxide ( 1 ) occurs in a chair-boat type equilibrium involving inversion of the lone pair on the N16 atom [ 20 ]; the N16-oxide of sparteine ( 2 ), previously thought to adopt the all chair conformation, has been found recently to have ring C in a boat conformation and a cis C/D ring junction [ 21 ]. Sparteine epi-N-oxide ( 3 ) has the C ring boat conformation and must be obtained by NaBH 4 reduction of lupanine N-oxide [ 20 ].…”

“…Sparteine N1-oxide ( 1 ) occurs in a chair-boat type equilibrium involving inversion of the lone pair on the N16 atom [ 20 ]; the N16-oxide of sparteine ( 2 ), previously thought to adopt the all chair conformation, has been found recently to have ring C in a boat conformation and a cis C/D ring junction [ 21 ]. Sparteine epi-N-oxide ( 3 ) has the C ring boat conformation and must be obtained by NaBH 4 reduction of lupanine N-oxide [ 20 ]. α-Isosparteine N-oxide ( 4 ) has a conformation identical to that of the free base ( Figure 1 ) [ 19 ].…”