Z. Lin / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 121 (2014) 254–258
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more information and knowledge regarding the structures of quin-
olones [3,4].
(S,S)-8-benzyl-2,8-diazabicyclo[4.3.0]nonane. The debenzylation
by catalytic hydrogenation over Pd/C gave (S,S)-2,8-diazabic-yclo-
[4.3.0]nonane. The reaction of 2,4,5-trifluoro-3-methoxybenzoyl
chloride with malonic acid monoethyl ester monopotassium
salt in the presence of triethylamine gave 2-(2,4,5-trifluoro-3-
methoxybenzoyl)acetic acid ethyl ester, which was condensed
with triethyl orthoformate to yield the corresponding ethoxymeth-
ylene derivative. The reaction of ethoxymethylene with cyclopro-
pylamine afforded the cyclopropylaminom-ethylene derivative,
which was finally cyclized to get 1-cyclopropyl-6,7-difluoro-8-
methoxy-4-oxo-1,4-dihydroquinoline-3-carboxylic acid by means
of NaF in DMF. (S,S)-2,8-diazabicyclo[4.3.0]nonane condensed with
1-cyclopropyl-6,7-difluoro-8-methoxy-4-oxo-1,4-dihydroquino-
line-3-carboxylic acid in basic medium produced the free base and
finally acidified with HCl, which resulted in the formation of the
hydrochloric salt. The molecular structures of free base and hydro-
chloride were shown in Figs. 1 and 2.
This paper reported the elaborations of the molecular structure
by Fourier-transform ion cyclotron resonance mass spectrometry
(FT-ICR-MS), as well as infrared spectra. Infrared absorption fre-
quencies of different groups were precisely attributed and the frag-
mentation pathways of CLF-HCl were investigated by electrospray
ionization multi-stage mass spectrometry (ESI-MSn). High resolu-
tion helped to improve the mass accuracy and precision by increas-
ing the assurance that the mass of the ion to be measured was not
skewed by an underlying interference. Product ion mass assign-
ment with an accuracy <5 ppm (parts per million) was attainable
when the ion mass could be determined via calculation from its
elemental composition [5].
The main goal in the current research was to explore the abun-
dant infrared and mass spectral information about this compound,
which would help us to analyze the similar quinolones by simple
IR and MS.
Results and discussion
Experiments
Infrared spectra
IR spectra were recorded on a Bruker VECTOR22 spectrometer.
MS was determined on Bruker Daltonics Apex ultra 7.0T Fourier
transform mass spectrometer with an Apollo ESI source. The condi-
tions employed for ESI source were a drying gas temperature of
180 °C, a nebulizing gas pressure of 2.0 L/min, with 4.0 kV on the
atmospheric side of the glass capillary, 3.5 kV on the atmospheric
chamber end cap shield, and the capillary exit voltage was kept
36 V to avoid capillary-skimmer dissociation in the ESI interface.
(10S, 60S)-1-cyclopropyl-7-(2,8-diazabicyclo[4.3.0] non-8-yl)-6-
fluoro-8-methoxy-4-oxo-1,4-dihydroquinoline-3-carboxylic acid
(free base, CLF) and its hydrochloride salt (CLF-HCl) was prepared
simply as the following method (Scheme 1): 8-benzyl-2,8-diazabi-
cyclo-[4.3.0]nonane-7,9-dione was reduced with LiAlH4 into
cis-8-benzyl-2,8-diazabicyclo[4.3.0]nonane. Subsequent optical
resolution of cis-8-benzyl-2,8-dia-zabicyclo[4.3.0]nonane was
performed by separation of the cis-(R,R)-isomer as crystalline
Since the IR spectrum of CLF-HCl had not been reported in de-
tails previously, it was necessary to assign the band of the bulk
spectra exactly. The band positions and assignments were listed
in Table 1. For the purpose of the discussion and assignments,
the salt was compared with the free base. Recorded infrared spec-
tra were shown in Figs. 3 and 4.
The region 4000–2400 cmꢁ1
From the recorded IR spectra, we could see that as the wave
number of adsorption peaks in the 4000–2400 cmꢁ1, significant
difference was observed between the salt and free base.
The OH stretching vibration of salt was shown at 3528.0 cmꢁ1
and the NH stretching vibration of was at 3472.6 cmꢁ1, whilst their
corresponding vibrations of free base were at 3588.1 cmꢁ1 and
3431.0 cmꢁ1 as little broad band, which indicated that OH and
NH were affected by the proton of hydrochloride.
L-(+)-tartrate salt and further purification of the cis-(S,S)-isomer
as the -(-)-tartrate salt afforded enantiomerically pure
D
Scheme 1. The synthesis scheme of CLF-HCl.