Improvement of the synthesis of diphenylmethyl 7β-(o-hydroxy)benzylideneamino-3-hydroxymethyl-3-cephem-4-carboxylate

Article abstract of DOI:10.1016/S0014-827X(01)01115-6

The title product (I) is synthesized currently from 7-aminocephalosporanic acid, and diphenyldiazomethane (DDM) is used as a protective reagent of the acid function for further reactions. When DDM was prepared from benzophenone hydrazone by reaction with chloramine T, it was resulted impure by p-toluenesulfonamide, formed as side product, which cannot be removed during the final purification step carried out according to the literature procedure. Two simple methods are proposed here to obtain I with the suitable degree of purity necessary for a drug.

Full text of DOI:10.1016/S0014-827X(01)01115-6

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Il Farmaco 56 (2001) 629–631
Short Communication
Improvement of the synthesis of diphenylmethyl
7b-(o-hydroxy)benzylideneamino-3-hydroxymethyl-
3-cephem-4-carboxylate
Miguel Lo´pez a, Zalua Rodr´ıguez a, Ba´rbara Valde´s a, Herma´n Velez a, Juan Agu¨ero a,
Adamo Fini b,*, Maritza Gonza´lez b,1
a Centro de Quimica Farmaceutica (CQF), A6e. 200 y 21, Atabey, Playa, Ciudad de La Habana, Ha6ana, Cuba
b Istituto di Scienze Chimiche, Via San Donato 15, Bologna, Italy
Received 2 February 2001; accepted 8 March 2001
Abstract
The title product (I) is synthesized currently from 7-aminocephalosporanic acid, and diphenyldiazomethane (DDM) is used as
a protective reagent of the acid function for further reactions. When DDM was prepared from benzophenone hydrazone by
reaction with chloramine T, it was resulted impure by p-toluenesulfonamide, formed as side product, which cannot be removed
during the final purification step carried out according to the literature procedure. Two simple methods are proposed here to
obtain I with the suitable degree of purity necessary for a drug. © 2001 Elsevier Science S.A. All rights reserved.
Keywords: Diphenyldiazomethane; p-Toluenesulfonamide; Purification
This compound was prepared by alkaline hydrolysis
of 7-ACA under mild conditions, followed by protec-
1. Introduction
tion of the amino group by formation of a Schiff base
with salicylaldehyde, and of the carboxyl group by
Diphenylmethyl - 7b - (o - hydroxy)benzylideneamino-
3-hydroxymethyl-3-cephem-4-carboxylate (I) (Fig. 1) is
esterification with diphenyldiazomethane (DDM) [1,2].
a synthetic intermediate in the preparation of a class of
This compound is used widely in reactions of
cephalosporins from 7-aminocephalosporanic acid (7-
cephalosporins because it requires mild conditions both
ACA), such as cefixime and cefdinir [1,2].
to protect and de-protect a carboxyl group, avoiding
side reactions, such as lactonization of the dihydrothi-
azine ring.
DDM is an unstable reagent that needs to be pre-
pared just before use. To obtain this compound from
benzophenone hydrazone, chloramine T is used cur-
rently as an oxidant in the presence of iodine, as a
catalyst of the process, in aqueous solution of DMA or
DMF. The resulting product is extracted of the reaction
mixture with dichloromethane, purified with sodium
hydrogen carbonate solution and dried. However, an
Fig. 1. Diphenylmethyl-7b-(o-hydroxy)benzylideneamino-3-hydrox-
ymethyl-3-cephem-4-carboxylate.
accurate analysis of a sample of this material prepared
for the synthesis of I, according to the proposed
method, showed the presence of an impurity (Table 1),
* Corresponding author.
E-mail address: fini@biocfarm.unibo.it (A. Fini).
1 Postgraduate fellow from CQF.
0014-827X/01/$ - see front matter © 2001 Elsevier Science S.A. All rights reserved.
PII: S0014-827X(01)01115-6

630
M. Lo´pez et al. / Il Farmaco 56 (2001) 629–631
Table 1
1 was applied in the synthesis of DDM. This compound
was dissolved in n-hexane, where it is highly soluble,
leaving a white solid, insoluble in this solvent, that was
filtered and recrystallized from n-hexane/ethylacetate
1:1 (v/v). The residue was identified as p-toluenesulfon-
amide (PTSA), as it emerges in Table 2, by comparing
with a pure sample [4,5].
Evidently in the previous papers the final washing
with a sodium hydrogen carbonate solution was ineffi-
cient because PTSA, formed as a by-product of DDM,
was not eliminated completely and still contaminated I
when the protection of the acid function in the cephem
nucleus was carried out in a subsequent step.
Characterization of I obtained with diphenyldiazomethane (literature
method)
IR [w (cm−1)]
1H NMR [l (ppm)]
Reported
3470
Obtained
Reported
Obtained
3470
3328
3240
1760
1700
2.3 (s, 3H)
3.70 (s, 2H)
4.20 (s, 2H)
5.20 (t, 1H)
5.31 (d, 1H) J=5
Hz
3.70 (s, 2H)
4.30 (s, 2H)
5.15 (br, 1H)
5.45 (d, 1H) J=5
Hz
1768
1710
1620
1620
5.71 (d, 1H) J=5
Hz
5.70 (d, 1H) J=5
Hz
Although Variant 1 allows the precipitation of PTSA,
a more practical way was developed for its removal
(Variant 2). It consists in washing the final solution of
DDM with a sodium hydroxide solution, since PTSA
forms soluble salts in diluted alkaline solution.
The effectiveness of these procedures was verified by
carrying out the synthesis of I with DDM obtained by
means of the two purification variants.
Yields (%)
78.1
m.p. (°C)
97–98.5
6.96 (s, 1H)
7.0–7.7 (m, 14H)
8.80 (s, 1H)
6.90 (s, 1H)
7.0–7.7 (m, 20H)
8.80 (s, 1H)
79.5
95–98
which cannot be eliminated following the literature
method [3]. We did not find any report in the literature
about this side product or suggestions for its elimina-
tion: in the case of cephalosporin synthesis this aspect
appears important since the impurity is associated with
the final drug, decreasing both the yield and melting
point (m.p.); additionally it introduces an unforeseen
variable and a potential toxic component into the in
vivo test.
Physical–chemical parameters for I, such as m.p., the
yield of the reaction, IR frequencies and 1H NMR
chemicals shift are reported in Table 1 for our sample
and compared with those found in the literature [3].
Yield and m.p. overlap. However, in the IR spec-
trum, besides the characteristic bands of I, the presence
2. Synthesis of DDM
Benzophenone hydrazone (10.78 g, 55 mmol) and
iodine (2.2 ml; 1% w/v) were dissolved in 60 ml aqueous
DMA (1:10, v/v). A solution of chloramine T (15.5 g,
55 mmol) in the same solvent was then added slowly
over 30 min at 20°C. The mixture was stirred for 15
min before partition between dichloromethane (110 ml)
and 5% (w/v) sodium hydrogen carbonate solution (275
ml). The dichloromethane layer was washed with water
(1×100 ml and 3×50 ml), dried on anhydrous sodium
sulfate and made up to 200 ml.
Variant 1. After drying, the final solution was evapo-
rated under reduced pressure until dryness. The residue
was treated with n-hexane (30 ml) and the obtained
suspension filtered. The separated solid was washed
with n-hexane (30 ml) three times. The filtrates were
combined and adjusted to a final volume of 200 ml with
n-hexane.
of two additional bands was observed at frequencies of
as
NH2
3328 (w
) and 3240 (wsNH2), not belonging to I and
1
appearing typical of a NH2 group. Moreover, in the H
NMR spectrum all the signals expected for I were
obtained, although a signal at 2.3 ppm was registered
corresponding to a methyl group (not a part of the
structure of I), as well as a number of signals in the
range of aromatic protons.
As a result there appears to be an impurity mixed to
the desired product. To identify the impurity a Variant
Variant 2. At the end of the reaction,
dichloromethane and sodium hydroxide solution 5%
Table 2
Characterization of the impurity and comparison with pure PTSA
1H NMR [l (ppm)]
EM (m/z)
m.p. (°C)
Obtained
Reported
Obtained
Reported
Obtained
CH3
NH2
H (3.5)
H (2.6)
2.30 (s, 3H)
7.27 (s, 2H)
7.36 (d, 2H)
7.71 (d, 2H)
171 (M+
155
91
)
171 (M+
155
91
)
135–137
133–135
65
65
39
39

M. Lo´pez et al. / Il Farmaco 56 (2001) 629–631
631
1
Table 3
group of PTSA. In the H NMR spectrum the disap-
pearance of the signal at 2.3 ppm was also observed, as
well as a reduction in the total number of protons of
the aromatic region (6). It was confirmed that through
both variants it was possible to remove PTSA from
DDM and, as a consequence, the presence of this
impurity in I. Examination of the differences between
the yields without and with purification of DDM sug-
gest that the impurity represented an important share
of the final product, as suggested by the large increase
of the m.p. of the final product.
We concluded that the reported method for prepar-
ing DDM from the oxidation of benzophenone hydra-
zone with chloramine T needs purification according to
either variants in order to obtain cephalosporanic
derivatives with a better degree of purity. According to
our results, the best melting point of I is 125–127°C
and not 97–98.5°C, as reported [2].
Results of the synthesis of I with purified DDM
Comp.
Yield (%)
m.p. (°C)
Reported [2]
I (with DDM without purification)
78.1
79.5
97–98.5
95–98
123–125
125–127
I (with DDM purified with n-hexane) 67.4
I (with DDM purified with 5%
65.1
NaOH)
(275 ml) were added. Then the procedure was similar to
the one described above.
3. Diphenylmethyl-7b-(o-hydroxy)benzylideneamino-
3-hydroxymethyl-3-cephem-4-carboxylate (I)
A suspension of 7-ACA (9.0 g, 33 mmol) in 120 ml
water/methanol 1:1(v/v) was added dropwise to 7 ml of
10 M sodium hydroxide solution at −20°C. The mix-
ture was stirred at −20°C for 25 min and the pH
adjusted to pH 7.5 with conc. HCl. The solution was
then added to salicylaldehyde (4.6 ml, 44 mmol) at
15°C. Stirring was continued at this temperature for 1
h, then pH was adjusted to 4.0–4.5 with 1 M HCl and
a solution of DDM (7.85 g, 4.0 mmol) in ethyl acetate
(43 ml) was added (Note 1). The mixture was stirred for
1 h and the pH was kept in this range. The resulting
mixture was extracted with ethyl acetate (275 ml). The
separated organic layer was washed with brine (2×200
ml), dried and evaporated under reduced pressure until
dryness. The residue was triturated in the presence of
n-hexane (20 ml), washed with n-hexane (3×20 ml)
and dried at 40°C during 1 h.
The notable increase of the m.p. suggests a higher
purity of the final product, and this fact represents an
important contribution both because the final drug is
purified from a potential toxic compound and because
the improvement is obtained using a very simple
method.
Acknowledgements
This work was supported in part by the Funds from
Ministero degli Affari Esteri (Italy) to M.G.C.
References
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The results are shown in Table 3.
When applying the two variants it can be noted that
the yield of the reaction decreased with respect to the
reference value, while the melting point of the product
increased.
The IR spectra of the I, obtained with purified
DDM, lack the bands corresponding to the amino
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