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Mass spectrometry of trimethylsilyl ethers carbohydrates
PRELIMINARY
273
COMMUNICATIONS
ACKNOWLEDGMENTS
It is a pleasure to acknowledge financial support from the National Research Council of Canada and the National Cancer Institute &f Canada. L. D. HALL J. F. MANVILLE
Department of Chemistry, The University of British Columbia, Vancouver 8, B. C. (Canada) REFERENCES
1 (a) S. L. MANNA-IT, D. D.
ELLEMANN, AND S. J. BROIS, J. Am. Chem. Sot., 87 (1965) 2220; (b) J. D. BALDEXHWIELER AND E. W. ~NDALL, Chem. Rev., 63 (1963) 81. 2 (0) R. R. FRAZER, R. U. LEhtrrux, AND J .D. STEVENS, J. Am. Chem. 83 (6) I. R. DYER, personal communication; (c) H. T. JENNINGS, B. COXON, AND K. A. MCLAUCHLAN, Abstract Papers Am. Chem. Sac. Meeting, 152 (1966) 10~; R. U. LEMIEUX, ibid., 1.52 (1966) 12~; cf- D. HURST AND A. G. MCINNES, Can. J. Chem., 43 (1965) 2004. 3 M. KARPLUS, J. Chem. Phys., 30 (1959) 11. 4 E. W. GARFSISCH, JR., J. Am. Chenr. SOL, 86 (1964) 5561, and references given therein. 5 J. A. POPLE AND A. A. BOTHNER-BY, J. Chem. Phys., 42 (1965) 1339. 6 R. FREEMAN AND D. H. WHIFFEN, Mol. Phys., 4 (1961) 321. 7 R. FREEn:..wa AND W. A. ANDERSON, J. Chem. Phys., 37 (1962) 2053. 8 A. D. BUCkXNGHAhf AND K. A. MCLAUCHLAN, Proc. Chem. SOL, (1963) 144. 9 H. M. MCCONNELL, J. Chem. Phys., 23 (195.5) 2454. 10 J. H. VAN VLECK AND A. SHERIDAN, Rev. Mod. Phys., 7 (1935) 167. 11 D. H. Buss, L. HOUGH, L. D. HALL, AND J. F. MANVILLE, Tetrahedron, 21 (1965) 69, and refer-
ences given therein. 12 S. L. ShrITH AND R. (Received
December
8th.
H.
COX,
J.
Mol.
Specrry.,
1966; in revised form,
16 (196%
January
23rd,
216.
1967)
Carbohyd. Res., 4 (1967) 271-273
Mass
spectrometry
of trimethylsilyl
ethers
of carbohydrates
Although partial hydrolysis is a widely applied method in the structural elucidation of polysaccharides, there is a need for small-scale and rapid procedures for establishing the structures of the oligosaccharides produced. In view of the results obtained with methyl ethers of disaccharides’, the use of mass spectrometry for this p-urpose seemed promising. In spite of recent improvements*, the exhaustive methylation of oligosaccharides is a complex and time-consuming operation. We were thus attracted to the use of the readily available trimethylsilyl ethers of sugars, since these compounds are volatile and have already found wide application in gas-liquid chromatography3. We now report on the mass spectra of trimethylsilyl ethers of D-glucose, D-galactose, D-mannose, L-arabinose, L-rhamnose, and their methyl glycosides, which can be considered as models for reducing and non-reducing residues of oligosaccharCarbohyd. Res., 4 (1967) 273-276
274
PRELIMINARY COMMUNICATIONS
ides. The peak of the molecular ion is absentfrom the mass spectra of these compounds. The ion M-15, probably resulting from the loss of a methyl group from a trimethylsilyl residue4, has the highest m/e value. The corresponding peak has low intensity. The peaks of the M-105 and M-195 ions, arising from the M-15 ion by splitting of one (90 m.u.) or two (180 m-u.) trimethylsilanol moIecuIes, are more intense. The most intense peaks in all of the spectra are those at m/e 204 and 217, corresponding to the ions (Me,SiO-CH =CH-OSiMe,)+ and Me,SiO-CH = CH-CH= &XMeJ, respectively, which are analogues ofthe ions having m/e 88 and 101 in mass spectra of methyl ethers of monosaccharides’. The peak at m/e 191 in the mass spectra of the trimethylsilyl ethers of monosaccharides also has a high intensity. The corresponding ion (Me,SiO-CH = 6SiMea) probably arises as a result of a rearrangement analogous to that leading to the J,-ion (m/e 75) for methylated methyl glycosides ‘. In agreement with such an assumption is the fact that the peak of the Jr-ion in the spectra of trimethylsilyl ethers of methyl glycosides is shifted to m/e 133, corresponding to Me,SiO-CH =6Me. The ion WesSiO-CH=C(OSiMe,)CH
Fig. 1. Partial mass spectra of the trimethylsilyl cellobiose (2), and laminaribiose (3). Carbohyd. Res., 4 (1967) 273-276
=dSiMe,]
having
m/e
305
ethers of 6-O-p-o-glucopyranosyl-D-galactose
is an
(I),
PRELIMINARY
COMMUNI CATIONS
275
analogue of the ion B2 (m/e 131) in-the spectra of methyl ethers5, and appears for all the compounds studied. The presence of relatively intense peaks at m/e 147, 103, and 73 is also characteristic of the mass spectra of trimethylsilyl ethers of the monosaccharides and methyl glycosides, the following structures being the most probable for these ions (c$ ref. 4): Me,Si-6 = SiMez m/e 147
+SiMe, m/e 73
CH1 = &SiMez m/e 103
The mass spectra of the disaccharides 6-0-j?-D-ghrcopyranosyl-D-galactose (l), cellobiose (2), Iaminaribiose (3) (see Fig. I), maltose, and lactose were also studied. There are characteristic differences between the mass spectra of disaccharides having different types of linkage. The peak at m/e 583 is present in the mass spectrum of the (1 -&)-linked disaccharide (l), whereas that at m/e 683 is characteristic for disaccharides 2 and 3. The mass spectrum of 2 can be distinguished from that of 3 by the presence of peaks at m/e 668 and 578. A structure analogous to that of the ion at m/e 305 can be assigned to the ion having m/e 683: D-G-0--CH=C-CH=&.,Mej
Me$iO-CH=C-CH=&Me3
I
O-D-G
\OSiMex
m/e 663
(from
21
m/e
663
(from
31
Loss of one methyl group from the ion having m/e 683 results in formation of the ion having m/e 668: 0
D-G -O
.
+QMe
I
Id
MeaSiO mje
683(from
--Me’*
D-G-0-&I-C=CH-hIMe
1
‘Me
OSiMe3
2)
m/e
660
(from
2)
D-G = 2,3.4.6-tetra-O-~trimethylsilyl~-D-glucopyranosyl.
The subsequent loss of a trimethylsilanol molecule from this ion gives the ion having m/e 578 (metastable peak at m/e 501). The symmetrical structure of the ion having m/e 683 (from 3) prevents the loss of a methyl radical, and results in the absence of the peaks at m/e 668 and 578, and the metastable peak at m/e 501, from the mass spectrum of the trimethylsilyl ether of laminaribiose. The ion having m/e 583 probably arises from the furanoid form of disaccharide 1:
6
F OTMS
.
D-G-0-CH,
0
H,OTMS-
OTMS
-Q -
OTMS
H,OTMS
+
D-G-0-CHa-CH&iMe3
OTMS
mje
583
OTMS
TMS
= trimethylsilyl
The formation of this ion from 2 and 3 is evidently impossible. Carbofyd.
Res.,
4 (1967)
273-276
276
PRELIMINARY
COMMUNI CATIONS
The ion corresponding to the peak at m/e 569 might be an anaiogue of the ions having m/e 191 and 133 (see above)_ CH20TMS
H,OTMS
OTMS
MesSi--&=CH-0 4
m/e
563
OTMS
This peak is present in the mass spectra of all of the disaccharides. However, its intensity depends to a large extent on the type of linkage. For example, the relative intensities are 4, 1.2, and 0.6% in the mass spectra of 1, 3, and 2, respectively. The intensity decreases with an increase in the spatial compression of the charged fragment Me,SiO+ = CH-O- by the neighbouring groups: the charged group is less hindered in position 6 than in positions 3 or 4. Thus, mass spectra may be used for detecting the types of linkage in disaccharides. The cotiguration of the glycosidic bond has no significant influence on the fragmentation pattern, as is evident from the mass spectra of the trimethylsilyl ethers of cellobiose and maltose. However, the fragmentation pattern depends on the configuration of the monosaccharide residues involved, these differences being more pronounced for trimethylsilyl ethers than for methyl ethers. For example, there are the relatively intense peaks at m/e 611, m/e 521, and m/e 445 (metastable peak), corresponding to the process 611+521, in the mass spectrum of the trimethylsiiyl ether of lactose, whereas these peaks are absent from the mass spectra of the maltose and cellobiose ethers. This result provides additional possibilities for the use of mass spectrometry in the study of the structures of ohgosaccharides. The authors thank Dr. V. N. Bochkarev and Mr. A. Sulima for assistance in the measurement of mass spectra_ Imtitute for Chemistry of NaturaZProducts, u. S. S. R. Academy of Sciences, ll!foscozu (U.
s.
s.
R.)
0. s. &IZHOV N_ V. MOLODTSOV N. K. KOCHETKOV
REFERENCES 1 0. S. CHIZHOV, L. A. POLYAKOVA, AND N. K. KOCHETSOV, Dokl. Akcrd. Mwk SSSR, 158 (1964) 685. 2 R. KUHN AND H. TRISCHMANN, Ber.,96 (1963) 284. 3 C. C. SWEELY, R. BEh?LEY, M. MAEITA, AND W_ W. WELLS, 3. Am. Chem. Sot., 85 (1963) 2491. 4 A.G. SHARKEY,R. A. FRIDEL,AND S.H.LANGER, Anal. Chem.,29 (1957) 770. 5 N. K. KOCHETKOV AND 0. S. CHIZHOV, Tetruhedrou, 21 (1965) 2029. (Receked
November
14th, 1966; in revised form, January 20th, 1967)
Carbohyd. Res., 4 (1967) 273-276
273
COMMUNICATIONS
ACKNOWLEDGMENTS
It is a pleasure to acknowledge financial support from the National Research Council of Canada and the National Cancer Institute &f Canada. L. D. HALL J. F. MANVILLE
Department of Chemistry, The University of British Columbia, Vancouver 8, B. C. (Canada) REFERENCES
1 (a) S. L. MANNA-IT, D. D.
ELLEMANN, AND S. J. BROIS, J. Am. Chem. Sot., 87 (1965) 2220; (b) J. D. BALDEXHWIELER AND E. W. ~NDALL, Chem. Rev., 63 (1963) 81. 2 (0) R. R. FRAZER, R. U. LEhtrrux, AND J .D. STEVENS, J. Am. Chem. 83 (6) I. R. DYER, personal communication; (c) H. T. JENNINGS, B. COXON, AND K. A. MCLAUCHLAN, Abstract Papers Am. Chem. Sac. Meeting, 152 (1966) 10~; R. U. LEMIEUX, ibid., 1.52 (1966) 12~; cf- D. HURST AND A. G. MCINNES, Can. J. Chem., 43 (1965) 2004. 3 M. KARPLUS, J. Chem. Phys., 30 (1959) 11. 4 E. W. GARFSISCH, JR., J. Am. Chenr. SOL, 86 (1964) 5561, and references given therein. 5 J. A. POPLE AND A. A. BOTHNER-BY, J. Chem. Phys., 42 (1965) 1339. 6 R. FREEMAN AND D. H. WHIFFEN, Mol. Phys., 4 (1961) 321. 7 R. FREEn:..wa AND W. A. ANDERSON, J. Chem. Phys., 37 (1962) 2053. 8 A. D. BUCkXNGHAhf AND K. A. MCLAUCHLAN, Proc. Chem. SOL, (1963) 144. 9 H. M. MCCONNELL, J. Chem. Phys., 23 (195.5) 2454. 10 J. H. VAN VLECK AND A. SHERIDAN, Rev. Mod. Phys., 7 (1935) 167. 11 D. H. Buss, L. HOUGH, L. D. HALL, AND J. F. MANVILLE, Tetrahedron, 21 (1965) 69, and refer-
ences given therein. 12 S. L. ShrITH AND R. (Received
December
8th.
H.
COX,
J.
Mol.
Specrry.,
1966; in revised form,
16 (196%
January
23rd,
216.
1967)
Carbohyd. Res., 4 (1967) 271-273
Mass
spectrometry
of trimethylsilyl
ethers
of carbohydrates
Although partial hydrolysis is a widely applied method in the structural elucidation of polysaccharides, there is a need for small-scale and rapid procedures for establishing the structures of the oligosaccharides produced. In view of the results obtained with methyl ethers of disaccharides’, the use of mass spectrometry for this p-urpose seemed promising. In spite of recent improvements*, the exhaustive methylation of oligosaccharides is a complex and time-consuming operation. We were thus attracted to the use of the readily available trimethylsilyl ethers of sugars, since these compounds are volatile and have already found wide application in gas-liquid chromatography3. We now report on the mass spectra of trimethylsilyl ethers of D-glucose, D-galactose, D-mannose, L-arabinose, L-rhamnose, and their methyl glycosides, which can be considered as models for reducing and non-reducing residues of oligosaccharCarbohyd. Res., 4 (1967) 273-276
274
PRELIMINARY COMMUNICATIONS
ides. The peak of the molecular ion is absentfrom the mass spectra of these compounds. The ion M-15, probably resulting from the loss of a methyl group from a trimethylsilyl residue4, has the highest m/e value. The corresponding peak has low intensity. The peaks of the M-105 and M-195 ions, arising from the M-15 ion by splitting of one (90 m.u.) or two (180 m-u.) trimethylsilanol moIecuIes, are more intense. The most intense peaks in all of the spectra are those at m/e 204 and 217, corresponding to the ions (Me,SiO-CH =CH-OSiMe,)+ and Me,SiO-CH = CH-CH= &XMeJ, respectively, which are analogues ofthe ions having m/e 88 and 101 in mass spectra of methyl ethers of monosaccharides’. The peak at m/e 191 in the mass spectra of the trimethylsilyl ethers of monosaccharides also has a high intensity. The corresponding ion (Me,SiO-CH = 6SiMea) probably arises as a result of a rearrangement analogous to that leading to the J,-ion (m/e 75) for methylated methyl glycosides ‘. In agreement with such an assumption is the fact that the peak of the Jr-ion in the spectra of trimethylsilyl ethers of methyl glycosides is shifted to m/e 133, corresponding to Me,SiO-CH =6Me. The ion WesSiO-CH=C(OSiMe,)CH
Fig. 1. Partial mass spectra of the trimethylsilyl cellobiose (2), and laminaribiose (3). Carbohyd. Res., 4 (1967) 273-276
=dSiMe,]
having
m/e
305
ethers of 6-O-p-o-glucopyranosyl-D-galactose
is an
(I),
PRELIMINARY
COMMUNI CATIONS
275
analogue of the ion B2 (m/e 131) in-the spectra of methyl ethers5, and appears for all the compounds studied. The presence of relatively intense peaks at m/e 147, 103, and 73 is also characteristic of the mass spectra of trimethylsilyl ethers of the monosaccharides and methyl glycosides, the following structures being the most probable for these ions (c$ ref. 4): Me,Si-6 = SiMez m/e 147
+SiMe, m/e 73
CH1 = &SiMez m/e 103
The mass spectra of the disaccharides 6-0-j?-D-ghrcopyranosyl-D-galactose (l), cellobiose (2), Iaminaribiose (3) (see Fig. I), maltose, and lactose were also studied. There are characteristic differences between the mass spectra of disaccharides having different types of linkage. The peak at m/e 583 is present in the mass spectrum of the (1 -&)-linked disaccharide (l), whereas that at m/e 683 is characteristic for disaccharides 2 and 3. The mass spectrum of 2 can be distinguished from that of 3 by the presence of peaks at m/e 668 and 578. A structure analogous to that of the ion at m/e 305 can be assigned to the ion having m/e 683: D-G-0--CH=C-CH=&.,Mej
Me$iO-CH=C-CH=&Me3
I
O-D-G
\OSiMex
m/e 663
(from
21
m/e
663
(from
31
Loss of one methyl group from the ion having m/e 683 results in formation of the ion having m/e 668: 0
D-G -O
.
+QMe
I
Id
MeaSiO mje
683(from
--Me’*
D-G-0-&I-C=CH-hIMe
1
‘Me
OSiMe3
2)
m/e
660
(from
2)
D-G = 2,3.4.6-tetra-O-~trimethylsilyl~-D-glucopyranosyl.
The subsequent loss of a trimethylsilanol molecule from this ion gives the ion having m/e 578 (metastable peak at m/e 501). The symmetrical structure of the ion having m/e 683 (from 3) prevents the loss of a methyl radical, and results in the absence of the peaks at m/e 668 and 578, and the metastable peak at m/e 501, from the mass spectrum of the trimethylsilyl ether of laminaribiose. The ion having m/e 583 probably arises from the furanoid form of disaccharide 1:
6
F OTMS
.
D-G-0-CH,
0
H,OTMS-
OTMS
-Q -
OTMS
H,OTMS
+
D-G-0-CHa-CH&iMe3
OTMS
mje
583
OTMS
TMS
= trimethylsilyl
The formation of this ion from 2 and 3 is evidently impossible. Carbofyd.
Res.,
4 (1967)
273-276
276
PRELIMINARY
COMMUNI CATIONS
The ion corresponding to the peak at m/e 569 might be an anaiogue of the ions having m/e 191 and 133 (see above)_ CH20TMS
H,OTMS
OTMS
MesSi--&=CH-0 4
m/e
563
OTMS
This peak is present in the mass spectra of all of the disaccharides. However, its intensity depends to a large extent on the type of linkage. For example, the relative intensities are 4, 1.2, and 0.6% in the mass spectra of 1, 3, and 2, respectively. The intensity decreases with an increase in the spatial compression of the charged fragment Me,SiO+ = CH-O- by the neighbouring groups: the charged group is less hindered in position 6 than in positions 3 or 4. Thus, mass spectra may be used for detecting the types of linkage in disaccharides. The cotiguration of the glycosidic bond has no significant influence on the fragmentation pattern, as is evident from the mass spectra of the trimethylsilyl ethers of cellobiose and maltose. However, the fragmentation pattern depends on the configuration of the monosaccharide residues involved, these differences being more pronounced for trimethylsilyl ethers than for methyl ethers. For example, there are the relatively intense peaks at m/e 611, m/e 521, and m/e 445 (metastable peak), corresponding to the process 611+521, in the mass spectrum of the trimethylsiiyl ether of lactose, whereas these peaks are absent from the mass spectra of the maltose and cellobiose ethers. This result provides additional possibilities for the use of mass spectrometry in the study of the structures of ohgosaccharides. The authors thank Dr. V. N. Bochkarev and Mr. A. Sulima for assistance in the measurement of mass spectra_ Imtitute for Chemistry of NaturaZProducts, u. S. S. R. Academy of Sciences, ll!foscozu (U.
s.
s.
R.)
0. s. &IZHOV N_ V. MOLODTSOV N. K. KOCHETKOV
REFERENCES 1 0. S. CHIZHOV, L. A. POLYAKOVA, AND N. K. KOCHETSOV, Dokl. Akcrd. Mwk SSSR, 158 (1964) 685. 2 R. KUHN AND H. TRISCHMANN, Ber.,96 (1963) 284. 3 C. C. SWEELY, R. BEh?LEY, M. MAEITA, AND W_ W. WELLS, 3. Am. Chem. Sot., 85 (1963) 2491. 4 A.G. SHARKEY,R. A. FRIDEL,AND S.H.LANGER, Anal. Chem.,29 (1957) 770. 5 N. K. KOCHETKOV AND 0. S. CHIZHOV, Tetruhedrou, 21 (1965) 2029. (Receked
November
14th, 1966; in revised form, January 20th, 1967)
Carbohyd. Res., 4 (1967) 273-276