Study of the fragmentation pathway of α-aminophosphonates by chemical ionization and fast atom bombardment mass spectrometry

Article abstract of DOI:10.1002/rcm.4938

The diastereoisomers of α-aminophosphonates are key intermediates in the synthesis of enantiomerically pure α-aminophosphonic acids, which are analogs of α-amino acids. Although several methods have been reported for the diastereoselective synthesis of α-aminophosphonates, their mass spectrometry (MS) fragmentation patterns have not yet been fully investigated. The work described here involved a detailed study of the fragmentation of enriched α-aminophosphonate diastereoisomers by chemical ionization (CI-MS) and fast atom bombardment (FAB)-MS. The complete characterization of the different conventional MS fragmentation pathways is represented and this intriguing exercise required the use of tandem mass spectrometry (MS/MS) experiments and high-resolution accurate mass measurements. All α-aminophosphonates gave prominent pseudomolecular ions, protonated molecules [MH]⁺, and their fragmentations mainly showed a loss of dimethyl phosphite to give the corresponding iminium ions as base peaks for α-aminophosphonates bearing methylbenzyl and 2,2-dimethylbutyl fragments. The loss of the chiral fragment from the iminium ions bearing the (S)-1-(1-naphthyl)ethyl group gave rise to a base peak due to aryl cations. The nature of all fragment ions were confirmed by high-resolution mass spectrometry (HRMS). Copyright

Full text of DOI:10.1002/rcm.4938

Research Article
Received: 2 December 2010
Revised: 17 January 2011
Accepted: 18 January 2011
Published online in Wiley Online Library
Rapid Commun. Mass Spectrom. 2011 25, 951–959
(wileyonlinelibrary.com) DOI: 10.1002/rcm.4938
Study of the fragmentation pathway of α‐aminophosphonates
by chemical ionization and fast atom bombardment mass
spectrometry
*
Gaurao D. Tibhe, Victoria Labastida‐Galván and Mario Ordóñez
Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos, Av. Universidad No. 1001, 62210
Cuernavaca, Mor., México
The diastereoisomers of α‐aminophosphonates are key intermediates in the synthesis of enantiomerically pure
α‐aminophosphonic acids, which are analogs of α‐amino acids. Although several methods have been reported for
the diastereoselective synthesis of α‐aminophosphonates, their mass spectrometry (MS) fragmentation patterns
have not yet been fully investigated. The work described here involved a detailed study of the fragmentation of
enriched α‐aminophosphonate diastereoisomers by chemical ionization (CI‐MS) and fast atom bombardment
(FAB)‐MS. The complete characterization of the different conventional MS fragmentation pathways is represented
and this intriguing exercise required the use of tandem mass spectrometry (MS/MS) experiments and high‐
resolution accurate mass measurements. All α‐aminophosphonates gave prominent pseudomolecular ions,
protonated molecules [MH]+, and their fragmentations mainly showed a loss of dimethyl phosphite to give the
corresponding iminium ions as base peaks for α‐aminophosphonates bearing methylbenzyl and 2,2‐dimethylbutyl
fragments. The loss of the chiral fragment from the iminium ions bearing the (S)‐1‐(1‐naphthyl)ethyl group gave rise
to a base peak due to aryl cations. The nature of all fragment ions were confirmed by high‐resolution mass
spectrometry (HRMS). Copyright © 2011 John Wiley & Sons, Ltd.
In the last 35 years there has been a tremendous leap in the
development of suitable synthetic methodologies for the
preparation of α‐aminophosphonic acids and their deriva-
tives, in optically pure form. In this context, several protocols
for the efficient asymmetric synthesis of α‐aminophosphonic
acids and derivatives have emerged in recent years and
several reviews have been published.[1]
α‐Aminophosphonic acids are mimetics of α‐amino acids.
In this class of compound, the planar and less bulky
carboxylic acid (CO2H) is replaced by a tetrahedral phos-
phonic acid functionality (P(O)(OH)2). This difference
between these two types of compound is reflected in their
shape, acidity, and several other properties. α‐Aminophos-
phonic acids and their derivatives have interesting biological
and biochemical properties and have found applications as
antibacterial, antiviral and antifungal agents, inhibitors of
enzymes, in the treatment of osteoporosis, and as haptens
for catalytic antibodies. These compounds are also commer-
cially important as insecticides and herbicides.[2] Some
racemic α‐aminophosphonates have potential anticancer
properties. These compounds have also been reported to
serve as starting materials for the preparation of potent
inhibitors of HIV‐1 protease. Many natural and synthetic
α‐aminophosphonic acids, their phosphonic esters and short
peptides incorporating these units exhibit a variety of
biological properties.[3] In addition, the incorporation of
cyclic amino acids with a medium‐sized ring into key
positions in peptide chains plays an important synthetic role,
and constitutes the most prominent pathway to conforma-
tionally constrained peptidomimetics, a widely used tool in
modern drug discovery.[4] However, it is well known that the
biological activity of the α‐aminophosphonic acids and
derivatives depends on the absolute configuration of the
stereogenic α‐carbon to phosphorus.[5]
Although several methods have been reported for the
diastereoselective synthesis of α‐aminophosphonates, the gas‐
phase mass spectrometry fragmentation patterns of these
compounds have not yet been fully investigated.[6] In
this context, and after our recent investigation on the
diastereoselective synthesis of α‐aminophosphonates in
a one‐pot reaction, we report here a detailed study of the
gas‐phase fragmentation pathway of several synthetic dia-
stereoisomerically enriched α‐aminophosphonates bearing
(S)‐α‐methylbenzylamine, (S)‐1‐(1‐naphthyl)ethylamine and
(S)‐3,3‐dimethyl‐2‐butylamine using chemical ionization
(CI)‐MS and fast atom bombardment (FAB)‐MS.
All the gas‐phase fragmentation routes and fragment ion
structures described here were elucidated on the basis of a
reasonable interpretation and were confirmed by MS/MS
linked‐scans under FAB‐MS conditions together with high‐
resolution accurate mass data.
* Correspondence to: M. Ordóñez, Centro de Investigaciones
Químicas, Universidad Autónoma del Estado de Morelos,
Av. Universidad No. 1001, 62210 Cuernavaca, Mor.,
México.
E-mail: palacios@ciq.uaem.mx
Rapid Commun. Mass Spectrom. 2011, 25, 951–959
Copyright © 2011 John Wiley & Sons, Ltd.

G. D. Tibhe, V. Labastida‐Galván and M. Ordóñez
EXPERIMENTAL
used was 99.999%. CI‐MS experiments in positive ion
form were performed with a temperature source at 230°
C, ionization energy of 200 eV, an ionization trap current of
300 μA, and methane was used as the reacting gas.
Fast atom bombardment (FAB) mass spectra in positive ion
detection mode were obtained in the same mass spectro-
meter at 10 eV emissions and 6 keV; the temperature
source was at 25°C, xenon gas was used for bombardment
and 3‐nitrobenzyl alcohol was used as matrix. A direct
insertion probe was used. Polyethylene glycols 600
were used as internal mass references in the HR‐MS
measurements. The scan range for these mass measure-
ments was set to include two standard peaks that
encompassed the sample peak of interest. Accurate mass
measurements were performed at a resolution of 10 000
(10% valley definition) and 120 s/decade, respectively. The
accurate mass was calculated as the mean of the
Instrumentation
A
high‐resolution double‐focusing mass spectrometer
with reversed geometry (JEOL MStation JMS‐700 mass
spectrometer) was used in the present work. The mass‐
analyzed ion kinetic energy spectrometric (MIKES) tech-
nique was employed to obtain the translational energy
spectra of product ions generated. Namely, the magnetic
sector field was adjusted to select the precursor ion and its
products were analyzed by scanning the electron
sector potential. Collision gas was introduced into the cell
located between magnetic and electric sectors. The gas
handling system was purged first and the collision
gas pressure was adjusted to yield 50% attenuation of the
precursor ion beam. The purity of the helium collision gas
O
H
N
R
O
O
P(OMe)2
no catalyst
R
NH2
+
+
H P(OMe)2
R'
no solvent
80 oC, 5-8 h
79-93%
H
Me
R'
70:30 to 93:7 dr
Me
1a-h; R = Ph
2a-i; R = 1-naphthyl
3a-j; R = t-Bu
R' = a; C6H5, b; 4-FC6H4, c; 4-ClC6H4, d; 4-MeOC6H4, e; Bn,
f;i-Bu, g; i-Pr, h; t-Bu, i; 3,4-di-MeOC6H3, j; 3-HOC6H4
Scheme 1. Uncatalyzed one‐pot diastereoselective synthesis of α‐aminophosphonates 1–3 in solvent‐free conditions.
O
H
P(OMe)2
R
+
O H
H
N
CH2
H
N
HO P(OMe)2
+
+
P(OMe)2
R
R
NH2
R'
7a-j
R'
Me
Me R'
+
+
4a-h; m/z = [M H] - 110
+
+
5a-i; m/z = [M H] - 110
+
+
6a-j; m/z = [M H] - 110
H
H
O
+
NH
R'
P(OMe)2
N
R
R'
Me
+
R
+
+
1a-h; m/z = [M H]
+
O
P(OMe)2
+
2a-i; m/z = [M H]
+
Me
H2N
+
3a-j; m/z = [M H]
8; R = Ph
9; R = 1-naphthyl
10; R = t-Bu
R'
Scheme 2. Proposed fragmentation pathway for the α‐aminophosphonates 1–3.
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Copyright © 2011 John Wiley & Sons, Ltd. Rapid Commun. Mass Spectrom. 2011, 25, 951–959

Fragmentation pathway of α‐aminophosphonates
values measured in 5–10 scans, determined from the
mass centroids of the ion peak of interest. Theoretical
elemental compositions were calculated within a mass
window of 10 ppm from the measured accurate mass
using the program installed in the data system; the
elemental composition with the theoretical mass that best
fitted the measured value, and that also made chemical
sense, was assigned to the ion. The fragmentation pathway
was confirmed by linked‐scanning BE in the 1st FFR (field‐
free region) and the spectra were measured using a
resolution of 3000.
by an uncatalyzed one‐pot reaction under solvent‐free
conditions. A mixture of the different reactants, which
contained an aliphatic or aromatic aldehyde, chiral amine
[(S)‐α‐methylbenzylamine, (S)‐1‐(1‐naphthyl)ethylamine or
(S)‐3,3‐dimethyl‐2‐butylamine] and dimethyl phosphite,
was heated at 80°C for 5–8 h (Scheme 1).[7]
RESULTS AND DISCUSSION
We report here a detailed study involving chemical ionization
(CI) and fast atom bombardment (FAB) mass spectrom-
etry (MS) of α‐aminophosphonates (1a–h, 2a–i and 3a–j)
(Scheme 2). In general, identical fragment ions were
observed under CI‐MS and FAB‐MS conditions for all 26
molecules studied, and therefore we propose a general
Synthetic methodology
The diastereoisomerically enriched α‐aminophosphonates
1a–h, 2a–i and 3a–j were easily prepared in excellent yields
+
H
N
O
H
P(OMe)
Me
(a)
(b)
(c)
1a
+
H
N
O
H
P(OMe)
Me
2a
+
H
N
O
H
P(OMe)
Me
3a
Figure 1. FAB‐MS spectra for the α‐aminophosphonates: (a) 1a, (b) 2a, (c) 3a.
Rapid Commun. Mass Spectrom. 2011, 25, 951–959 Copyright © 2011 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/rcm

G. D. Tibhe, V. Labastida‐Galván and M. Ordóñez
gas‐phase fragmentation pattern involving several path-
ways. All of the α‐aminophosphonates exhibit prominent
peaks for protonated molecules [M+H]+ together with
the protonated dimer cluster [2M+H]+.
ions [R′CH = NH2]+ 7a–j, which were observed in low
abundance. The iminium ions [R′CH = NHCHCH3R]+ 4–6
also lost the fragment [R′CH = NHCHCH3R – R′CH = NH]+
to give the fragment ions [CH3CHR]+; 8 (R = Ph, m/z = 105), 9
(R = 1‐naphthyl, m/z = 155) and 10 (R = t‐Bu, m/z = 85). The
fragment ions 9 correspond to the base peak upon FAB
ionization. It can be seen from Scheme 2 that the fragment
ions [CH3CHR]+ 8–10 (second fragmentation pathway)
should also be formed from the protonated molecule
[M+H]+ through loss of the corresponding α‐amino-
The corresponding iminium fragment ion [M–HP(O)(OMe)2]+
(at m/z = [M+H]+ –110) was attributed to the protonated
molecule [M+H]+ losing a mass of 110 Da, which corresponds
to the loss of dimethyl phosphite HP(O)(OMe)2; [4a–h; R= Ph,
5a–i; R =1‐naphthyl, and 6a–j; R =t‐Bu]. Such a process has been
proposed in theoretical studies[8] and the peak was assigned to
[R′CH = NHCHCH3R]+. These latter iminium fragment ions
4a–h and 6a–j correspond to the base peak in FAB ionization.
Additionally, the iminium ions 4–6 lose the fragment
[R′CH = NHCHCH3R ‐ RCH = CH2]+ to afford the iminium
phosphonate; however,
a detailed study by tandem
mass spectrometry (MS/MS) showed that the frag-
ment ions [CH3CHR]+ 8–10 are formed directly from
the iminium ions [R′CH = NHCHCH3R]+ 4–6. The spectra
+
H
N
O
H
P(OMe)
2
Me
1a
(a)
(b)
(c)
+
H
N
O
H
P(OMe)2
Me
2a
+
H
N
O
H
P(OMe)2
Me
3a
Figure 2. CI‐MS spectra for the α‐aminophosphonates: (a) 1a, (b) 2a, (c) 3a.
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Copyright © 2011 John Wiley & Sons, Ltd. Rapid Commun. Mass Spectrom. 2011, 25, 951–959

Fragmentation pathway of α‐aminophosphonates
for the α‐aminophosphonates 1a–3a are shown in Figs. 1–3.
The formation of each fragment ion was confirmed by FAB
high‐resolution studies and the results are summarized in
Tables 1–3.
fragmentation of the α‐aminophosphonates involved the loss of
dimethyl phosphite to give the iminium ions as the base peak.
Additionally, all fragment ions were confirmed by a detailed
interpretation of MS/MS experiments and by high‐resolution
mass spectrometry.
CONCLUSIONS
Acknowledgements
The uncatalyzed one‐pot, three‐component diastereoisomerically
enriched synthesis of α‐aminophosphonates 1–3 was carried out
under solvent‐free conditions and gave excellent yields. The
products were fully characterized and their complete elucidation
by CI‐MS and FAB‐MS is an intriguing exercise. The main
This work was carried out with the financial support of
CONACYT‐MEXICO (Project 41657‐Q) and CONACYT‐CSIC
(Projects J000.400/2009 and 2008MX0044). G.T. also wishes
to thank CONACYT for a Graduate Scholarship (228881).
H
+
N
Me
4a
(a)
+
+
H
N
O
H
P(OMe)
Me
8a
Me
1a
+
Me
H
+
9a
N
(b)
Me
+
H
N
O
H
P(OMe)
5a
Me
2a
H
+
H
N
O
H
+
N
+
P(OMe)
Me
10a
Me
Me
6a
3a
(c)
Figure 3. FAB‐MS tandem‐MS/MS spectra for the α‐aminophosphonates, showing the precursor and product ion: (a) 1a,
(b) 2a, (c) 3a.
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G. D. Tibhe, V. Labastida‐Galván and M. Ordóñez
Table 1. Relative abundance (%) of selected ions in CI and FAB mass spectra for compounds 1a–h
Compound
+
H
N
Ph
NH2
R'
+
O H
H
N
+
Ph
P(OMe)2
Ph
Me
Me R'
8a-h
7a-h
R'
1a-h
Me
4a-h
320 (100)a
320 (25)b
320.1433c
320.1416d
1a; R’ = C6H5
1b; R’ = 4‐FC6H4
1c; R’ = 4‐ClC6H4
1d; R’ = 4‐MeOC6H4
1e; R’ = Bn
210 (53)
105 (5)
106 (4)
210 (100)
210.1288
210.1283
C15H16N
228 (100)
228(100)
228.1207
228.1189
C15H15FN
244 (100)
244 (100)
244.0928
244.0893
C15H15ClN
240 (100)
240 (100)
240.1398
240.1388
C16H18NO
224 (29)
224 (100)
224.1445
224.1439
C16H18N
190 (100)
190 (100)
190.1590
190.1596
C13H20N
176 (44)
105 (58)
105.0705
105.0704
C8H9
105 (12)
105 (79)
105.0695
105.0704
C8H9
106 (45)
106.0661
106.0657
C7H8N
124(7)
124 (43)
124.0550
124.0563
C7H7FN
140 (33)
140 (29)
140.0203
140.0267
C7H7ClN
136 (4)
C17H23NO3Pe
338 (92)a
338 (21)b
c
338.1317
338.1321d
C17H22FNO3Pe
354 (47)a
105 (68)
105 (95)
105.0680
105.0704
C8H9
354 (25)b
354.1033c
354.1026d
C17H22ClNO3Pe
350 (17)a
105 (4)
350 (11)b
105 (54)
105.0702
105.0704
C8H9
136 (40)
136.0761
136.0762
C8H10NO
120(4)
350.1498c
350.1521d
C18H25NO4Pe
334 (100)a
334 (30)b
105 (5)
105 (89)
105.0695
105.0704
C8H9
120 (62)
120.0819
120.0813
C8H10N
86 (21)
c
334.1578
d
334.1572
C18H25NO3Pe
300 (72)a
1f; R’ = i‐Bu
105 (25)
105 (45)
105.0713
105.0704
C8H9
300 (45)b
86 (27)
300.1747c
86.0967
86.0970
C5H12N
72 (2)
300.1729d
C15H27NO3Pe
286 (100)a
286 (30)b
1g; R’ = i‐Pr
105 (7)
176 (100)
176.1437
176.1439
C12H18N
190 (74)
190 (100)
190.1589
190.1596
C13H20N
105 (54)
105.0707
105.0704
C8H9
72 (34)
286.1577c
72.0816
72.0813
C4H10N
86 (2)
286.1572d
C14H25NO3Pe
300 (100)a
300 (14)b
1h; R’ = t‐Bu
105 (5)
105 (42)
105.0713
105.0704
C8H9
86 (30)
300. 1726c
300.1729d
C15H27NO3Pe
86.0964
86.0970
C5H12N
aIons by CI‐MS.
bIons by FAB‐MS.
cHRMS observed by FAB‐MS.
dHRMS calculated.
eElemental composition.
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Copyright © 2011 John Wiley & Sons, Ltd. Rapid Commun. Mass Spectrom. 2011, 25, 951–959

Fragmentation pathway of α‐aminophosphonates
Table 2. Relative abundance (%) of selected ions in CI and FAB mass spectra for compounds 2a–i
Compound
Ar
H
N
NH2
R'
O H
H
N
+
Ar
P(OMe)2
Ar
Me
9a-i
Me
5a-i
R'
7a-i
R'
2a-i
Me
2a; R’ = C6H5
370 (7)a
260 (100)
260 (35)
260.1426
260.1439
C19H18N
294 (89)
294 (27)
294.1038
294.1050
C19H17ClN
290 (100)
290 (78)
290.1527
290.1545
C20H20NO
274 (100)
274 (21)
274.1557
274.1596
C20H20N
240 (100)
240 (35)
240.1762
240.1752
C17H22N
226 (73)
226 (41)
226.1604
226.1596
C16H20N
240 (100)
240 (46)
240.1735
240.1752
C17H22N
320 (100)
320 (70)
320.1625
320.1651
C21H22NO2
155 (73)
155 (100)
155.0871
155.0861
C12H11
155 (84)
155 (100)
155.0874
155.0861
C12H11
155 (51)
155 (100)
155.0878
155.0861
C12H11
155 (77)
155 (100)
155.0865
155.0861
C12H11
155 (76)
155 (100)
155.0843
155.0861
C12H11
155 (37)
155 (100)
155.0851
155.0861
C12H11
155 (97)
155 (100)
155.0871
155.0861
C12H11
155 (63)
155 (100)
155.0817
155.0861
C12H11
106(14)
106 (20)
106.0661
106.0657
C7H8N
370 (8)b
370.1604c
370.1572d
C21H25NO3Pe
404 (100)a
404(11)b
2c; R’ = 4‐ClC6H4
2d; R’ = 4‐MeOC6H4
2e; R’ = Bn
140(10)
140 (11)
140.0255
140.0267
C7H7ClN
136(10)
136 (26)
136.0780
136.0762
C8H10NO
120 (19)
120 (16)
120.0809
120.0813
C8H10N
86 (7)
404.1180c
404.1182d
C21H24ClNO3Pe
400 (3)a
400(20)b
400.1647c
400.1678d
C22H27NO4Pe
384 (98)a
384 (9)b
384.1721c
384.1729d
C22H27NO3Pe
350 (72)a
2f; R’ = i‐Bu
350 (12)b
86 (14)
350.1904c
350.1885d
C19H29NO3Pe
336 (100)a
336 (12)b
86.0963
86.0970
C5H12N
72 (2)
2g; R’ = i‐Pr
72 (15)
336.1713c
336.1729d
C18H27NO3Pe
350 (11)a
72.0808
72.0813
C4H10N
86 (7)
2h; R’ = t‐Bu
350 (5)b
86 (18)
350.1858c
350.1885d
C19H29NO3Pe
430 (74)a
86.0960
86.0970
C5H12N
166 (33)
166 (22)
166.0829
166.0868
C9H12NO2
2i; R’ = 3,4‐di‐MeOC6H3
430 (10)b
430.1779c
430.1783d
C23H29NO5Pe
Ar = 1‐naphthyl.
aIons by CI‐MS.
bIons by FAB‐MS.
cHRMS observed by FAB‐MS.
dHRMS calculated.
eElemental composition.
Rapid Commun. Mass Spectrom. 2011, 25, 951–959 Copyright © 2011 John Wiley & Sons, Ltd.
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G. D. Tibhe, V. Labastida‐Galván and M. Ordóñez
Table 3. Relative abundance (%) of selected ions in CI and FAB mass spectra for compounds 3a–j
Compound
t-Bu
H
N
NH2
R'
+
O H
H
N
+
t-Bu
P(OMe)2
t-Bu
Me
10a-j
7a-j
R'
Me
6a-j
R'
3a-j
Me
3a; R’ = C6H5
300 (100)a
300 (25)b
300.1726c
300.1729d
190 (16)
85 (0)
106 (1)
190 (100)
190.1589
190.1596
C13H20N
208 (100)
208 (100)
208.1500
208.1502
C13H19FN
224 (21)
85 (6)
106 (31)
106.0651
106.0657
C7H8N
85.1021
85.1017
C6H13
85 (0)
C15H27NO3Pe
318 (21)a
3b; R’ = 4‐FC6H4
3c; R’ = 4‐ClC6H4
3d; R’ = 4‐MeOC6H4
3e; R’ = Bn
124 (6)
318 (31)b
85 (8)
124 (28)
124.0574
124.0563
C7H7FN
140 (0.5)
140 (28)
140.0294
140.0267
C7H7ClN
136 (1)
318.1639c
318.1634d
C15H26FNO3Pe
334 (100)a
334 (29)b
85.1022
85.1017
C6H13
85 (0)
224 (100)
224.1206
224.1206
C13H19ClN
220 (100)
220 (100)
220.1725
220.1701
C14H22NO
204 (87)
85 (12)
85.1022
85.1017
C6H13
85 (0)
334.1345c
334.1339e
C15H26ClNO3Pe
330 (46)a
330 (16)b
85 (4)
136 (25)
136.0745
136.0762
C8H10NO
120 (3)
330.1828c
330.1834d
C16H29NO4Pe
314 (100)a
314 (28)b
85.1015
85.1017
C6H13
85 (1)
204 (100)
204.1768
204.1752
C14H22N
170 (100)
170 (100)
170.1918
170.1909
C11H24N
156 (100)
156 (100)
156.1758
156.1752
C10H22N
170 (100)
170 (100)
170.1895
170.1909
C11H24N
250 (100)
250 (100)
250.1806
250.1807
C15H24NO2
206 (100)
206 (100)
206.1555
206.1545
C13H20NO
85 (7)
120 (32)
120.0816
120.0813
C8H10N
86 (5)
314.1870c
314.0946d
C16H29NO3Pe
280 (77)a
85.1014
85.1017
C6H13
85 (1)
3f; R’ = i‐Bu
280 (29)b
85 (1)
86 (19)
280.2028c
280.2040d
C13H31NO3Pe
266 (10)a
85.1029
85.1017
C6H13
85 (0)
86.0979
86.0970
C5H12N
72 (3)
3g; R’ = i‐Pr
266 (25)b
85 (7)
72 (21)
266.1874c
266.1885d
C12H29NO3Pe
280 (6)a
85.1013
85.1017
C6H13
85 (0)
72.0807
72.0813
C4H10N
86 (3)
3h; R’ = t‐Bu
280 (19)b
85 (4)
86 (17)
280.2062c
280.2042d
C13H31NO3Pe
360 (59)a
85.1005
85.1017
C6H13
85 (0)
86.0964
86.0970
C5H12N
166 (1)
3i; R’ = 3,4‐di‐MeOC6H3
3j; R’ = 3‐HOC6H4
360 (15)b
85 (4)
166 (21)
166.0870
166.0868
C9H12NO2
122 (0)
122 (32)
122.0602
122.0606
C7H8NO
360.1939c
360.1950d
C17H31NO5Pe
316 (17)a
85.1013
85.1017
C6H13
85 (0)
316 (21)b
85 (6)
316.1656c
316.1678d
C15H27NO4Pe
85.1009
85.1017
C6H13
aIons by CI‐MS.
bIons by FAB‐MS.
cHRMS observed by FAB‐MS.
dHRMS calculated.
eElemental composition.
wileyonlinelibrary.com/journal/rcm
Copyright © 2011 John Wiley & Sons, Ltd. Rapid Commun. Mass Spectrom. 2011, 25, 951–959

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Rapid Commun. Mass Spectrom. 2011, 25, 951–959 Copyright © 2011 John Wiley & Sons, Ltd.
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