bis - quinolizidine alkaloids produced by lupine species have generated much interest because of their valuable pharmacological properties . both pharmacological and toxicological properties of these alkaloids are well known [ 1 , 2 ] . sparteine appears to offer protection to plants from leguminosae family against insects and grazing mammals [ 3 , 4 ] . several bis - quinolizidine alkaloids ( sparteine , lupanine , 17-oxosparteine , 13-hydroxylupanine , angustifoline , etc . ) show antihypertensive , antipyretic , anti - inflammatory , antiarrhythmic , diuretic , hypoglicemic , hypotensive , antidiabetic , respiratory depressant and stimulant , and uterotonic properties [ 5 , 6 ] . the mass spectrometry study of bis - quinolizidine alkaloids has been stimulated by the evidence of the method 's ability to distinguish their stereoisomers , metamers , and positional isomers [ 714 ] . the main characteristic of the so - called  hard  electron - impact induced ionization ( ei ) of mass fragmentation of bis - quinolizidine alkaloid molecular ions is the dependence of the fragmentation pathway of the bis - quinolizidine skeleton on the stereochemistry of the a / b and c / d ring junctions . the stereochemical effects that are encountered with dissociations of stereoisomers incorporating saturated heterocycles rings are due to the ability of chemical bonds to be broken or formed . mass spectrometry includes a broad range of techniques that have allowed us to prove the detailed structures of organic compounds in a variety of ways . fast atom bombardment ionization ( fab ) is classified as a soft ionization technique in mass spectrometry and is well suited to organic compounds which contain a basic functional group . those compounds tend to run well in positive ion mode . in the positive fab technique a high velocity , rare gas atom molecular beam was produced in the ionization source , and directed onto the sample which was in solution ( in the matrix ) on a target , thus causing desorption of protonated molecular ions from the sample . generally , positive fab produces protonated molecular ions m+h with a little fragmentation , and there are some limitations because the presence of matrix gives rise to matrix - related ions . if , by chance , the sample give rise to ions at anyone of the m / z values of matrix , than the matrix should be changed . there are many references in the literature for different matrices where their molecular formulae and masses , their most frequently encountered m / z ions , and their uses have been summarized .   as a continuation of our previous study   it seems reasonable to extend investigation over fab mass fragmentation of isomeric oxo - substituted sparteine derivatives . fab - ms gives useful information for the chemical characterization of different types of alkaloids [ 16 , 17 ] . fast atom bombardment ( fab ) mass spectral behaviour of oxo - substituted sparteine derivatives has not been reported in the literature . in a previous work   we described the fragmentation routes of seven bis - quinolizidine alkaloids under fast atom bombardment conditions . we have shown that positional isomers of sparteine derivatives can be differentiated on the basis of their fab mass spectra . the aim of this study was to explain the fab mass fragmentation of isomeric sparteine lactams , for example , 2-oxosparteine ( lupanine ) 1 , 15-oxosparteine 2 , 17-oxosparteine 3 , 2,17-dioxosparteine ( 17-oxolupanine ) 4 , 2,13-dioxosparteine ( 13-oxolupanine ) 5 , 2-oxo-13-hydroxysparteine ( 13-hydroxylupanine ) 6 , and 2-oxo-17-hydroxysparteine ( 17-hydroxylupanine ) 7 ( figure 1 ) . these compounds consist of four rings , two of which ( a / b ) form a sofa / chair system of trans quinolizidine , the second trans system ( c / d ) form a boat / chair conformations . on the basis of the analysis of the fragmentation processes of 17 in the fab conditions we wished to establish whether it would be possible to distinguish the positional isomers ( 13 ; 4,5 ; 6,7 ) ( figure 1 ) . compounds 17 were obtained in the form of free basis according to literature methods [ 1824 ] . their spectral characteristics were consistent with the literature data [ 1824 ] . the fab spectra were produced using 3-nitrobenzyl alcohol ( m - nba ) as matrix . these spectra were recorded in positive mode on an amd - intectra gmbh harpstedt d-27243 model 604 two - sector mass spectrometer . for the collision - induced dissociation ( cid ) experiments , helium was used as a collision gas in the first field - free region ( 1ffr ) at a pressure corresponding to 50% attenuation of the precursor ion signal . the mass spectrometric behaviour of isomeric 17 was investigated in details by the positive fab mass spectrometry combined with cid . the relative abundances of characteristic peaks of even - electron as well as matrix - derived ions are presented in table 1 .   on the basis of fab and fab / cid mass spectra of 17 , the fab mass fragmentations of these compounds are shown in scheme 1 . in the fab spectra of 17 apart from the expected protonated [ m+h ] 
 a ions , there are also fragment ions . fragmentation of the cyclic m+h 
 a of 1 , 2 , and 3 ( scheme 1 , table 1 ) proceeds by the cleavages of two bonds of ring b and c of the sparteine skeleton . the cleavages of c6-c7 and c9-c10 bonds of ring b ( for 1 ) or c9-c11 and c7-c17 ones of ring d ( for 2 and 3 ) lead to the even - electron fragment ions d [ c9h15n+h ] , at m / z 138 . the cleavages of c7-c17 and n16-c17 bonds of ring c ( for 3 ) lead to the even - electron fragment ion b [ c14h24n2+h ] [ m+h - co ] , at m / z 221 . it should be pointed out that the origin of the even - electron fragment ions b and d has been confirmed by the fab / cid mass spectra of 13 . the even - electron fragment ions a [ m+h ] gives the base peaks for the spectra of 2 and 3 . in the fab mass spectrum of 1 fragmentation of the cyclic protonated molecule m+h of 3 ( table 1 ) proceeds also by the cleavages of n16-c17 and c17-c7 bonds of ring c with elimination of the neutral molecule of carbon monoxide and leads to the even - electron fragment ion b [ c14h24n2+h ] [ m+h - co ] at m / z 221 . it ought to be pointed out that in the molecules 2 and 3 in the bis - quinolizidine skeleton a and b rings form a trans double - chair system that is relatively resistant ( for thermodynamic reasons ) to conformational - configurational changes than a / b trans - fused rings with sofa / chair conformation of the molecule of 1 . this suggests that the structure of 2 and 3 increases the stability of m+h ions of these compounds in comparison with that of m+h ion of 1 . on the other hand the localization of oxo groups in the different position in bis - quinolizidine skeleton , that is , at c2 ( ring a ; 1 ) , at c15 ( ring d ; 2 ) and c17 ( ring c ; 3 ) influences clearly on the elimination of the neutral molecule of carbon monoxide from m+h ion of 3 . such ejection of co has been seen previously in the ei mass fragmentation of the molecular ion of 17-oxosparteine . the differences in the relative abundances of ions a in the spectra of 13 depend clearly on the differences in the conformations of bis - quinolizidine skeleton of these compounds .   in the light of these data isomeric compounds 1 , 2 , and 3 can be distinguished from each other on the basis of the differences in the relative abundances of ions a and d ( table 1 , scheme 1 ) as well as the presence of the even - electron fragment ion b [ m+h - co ] in the fab mass spectrum of 3 . the common characteristic features of the fab fragmentation of the protonated molecules [ m+h ] 
 a of 4 and 5 are the cleavages of bonds of rings b and c ( c6-c7 and c9-c10 as well as c7-c17 and c9-c11 , resp . ) . the fragment ions d [ c9h12no+h ] at m / z 151 were obtained in this way by fab fragmentation ( table 1 , scheme 1 ) . it should be pointed out that the even - electron ions [ m+h ] are the base peaks in the fab spectra of 4 and 5 . in the fab fragmentation of 5 ( table 1 , scheme 1 ) the elimination of a neutral molecule of water from the enol - tautomeric form of the [ m+h ] molecule of 5 , that is , the cleavage of c13-o bond of ring d leads to the even - electron fragment ion c. isomers 4 and 5 can be distinguished by the presence of even - electron fragment ion [ m+h - h2o ] 
 c [ c15h20n2o+h ] at m / z 245 in the fab spectrum of 5 . the absence of the elimination of water in the fab mass fragmentation of m+h 
 a ion of 4 is probably causes by neighbouring heteroatom participation in the elimination of this small molecule . protonated 4 shows no fragmentation by loss of water than does protonated 5 . in 4 the proton forms a hydrogen - bridge between oxygen a nitrogen atom of enol - tautomeric form of 4 thus stabilizing the ion . no such stabilization is possible in enol - tautomeric forms of 5 which undergoes fast elimination of water ( figure 2 ) . the common characteristic features of the fab fragmentation of 6 and 7 are the cleavages of c7-c17 and c9-c11 bonds of ring c of the lupanine skeleton . the fragment ions d [ c9h12no+h ] at m / z 151 are obtained in this way of fab fragmentation . in the fab mass spectra of 6 and 7 there are also even - electron fragment ions c [ c15h22n2o][m+h - h2o ] at m / z 247 . in the fab mass spectrum of 6 the base peak is ion [ m+h ] 
 a and in the fab mass spectrum of 7 the base peak is ion c. the differences in the relative abundances of ions a , c , and d in the fab spectra 6 and 7 allow differentiation of these positional isomers . it ought to be pointed out that the water loss is much more favourable in the fab mass fragmentation of 7 than 6 because after this elimination in the even - electron fragment ion c of 7 the charge is probably situated on the annular nitrogen atom n16 , and in the case of 6 the charge is probably situated on the carbon atom c13 . identification and structural characterisation of isomeric bis - quinolizidine alkaloids is an important problem in their analysis . mass spectrometry is a powerful tool for unambiguous determination of the structure of these compounds . in the literature that is no information about the fab mass fragmentation of bis - quinolizidine alkaloids . the present study has demonstrated that fab mass fragmentation of isomers of lactams of sparteine sparteine 17 ( 13 ; 4 , 5 ; 6 , 7 ) could be expressed as follows . ( 1 ) the fab mass fragmentation of the protonated molecules m+h of 17 proceeds mainly by the cleavages of bonds in b ( c6-c7 and n1-c10 ) ring and c ( c9-c11 , c7-c17 ) ring of the bis - quinolizidine skeleton ( table 1 , scheme 1 ) . ( 2 ) the protonated molecules m+h of investigated isomers 17 follow the common fragmentation pathways , but with differences in the relative abundances of fragment ions ( table 1 ) . ( 3 ) the differences in the relative abundances of fragment ions depend mainly on the location of the carbonyl function in the bis - quinolizidine skeleton . ( 4 ) the differences in the relative abundances of fragmentation ions depend also on the stereochemistry of a / b and c / d ring junctions of investigated 17 . ( 5 ) the main fab fragmentation of 3 involves also elimination of the neutral molecule of carbon monoxide [ ( m+h - co ) ] 
 m / z 221 ( table 1 ) . ( 6 ) the main fab mass fragmentation of 6 and 7 involves also elimination of the h2o neutral molecule , yielding ions at m / z 245 [ m+h - h2o ] ( 5 ) and m / z 247 [ m+h - h2o ] ( 6 , 7 ) , respectively ( table 1 ) . ( 7 ) the differences in relative abundances of even - electron ions a and d ( table 1 ) in the fab mass spectra of 1 , 2 , and 3 and the presence of even - electron ion b [ m+h - co ] in the fab mass spectrum of 3 allow differentiation of positional isomers 1 , 2 , and 3 . ( 8) the presence of even - electron fragment ion [ m+h - oh ] c allow differentiation of positional isomers 4 and 5 ( table 1 ) . ( 9 ) the differences in the relative abundances of ions a , c , and d in the fab mass spectra of 6 and 7 allow differentiation of these positional isomers .
the unpublished in the literature fab mass spectral fragmentation of seven oxosparteines ( i.e. , 2-oxosparteine , 15-oxosparteine , 17-oxosparteine , 2,17-dioxosparteine , 2,13-dioxosparteine , 2-oxo-13-hydroxysparteine , and 2-oxo-17-hydroxysparteine ) is investigated . 
 fragmentation pathways , elucidation of which was assisted by fab / collision - induced dissociation ( cid ) mass spectra measurements , are discussed . 
 the data obtained create the basis for distinguishing positional isomers .