Bis-trimethylsilyl cefamandole and process therefor

Bis-trimethylsilyl cefamandole is useful for regenerating cefamandole of excellent purity.

BACKGROUND OF THE INVENTION 
Cefamandole is a cephalosporin antibiotic which is useful for combating 
infectious diseases such as enterobacter infections as disclosed in U.S. 
Pat. No. 3,903,278. Cefamandole is 
7-(D-mandelamido)-3-(1-methyl-1,2,3,4-tetrazol-5-yl)thiomethyl- 
3-cephem-4-carboxylic acid and was first disclosed by Ryan in U.S. Pat. 
No. 3,641,021, Example 5. The process for making cefamandole by acylating 
"tetrazole nucleus," 7-amino-3-(1-methyl-1,2,3,4-tetrazol-5-yl) 
thiomethyl-3-cephem-4-carboxylic acid, with D-anhydro O-carboxymandelic 
acid is described by Greene in U.S. Pat. No. 3,840,531. The silylation of 
a cephalosporin nucleus is described by Jackson in U.S. Pat. No. 
3,671,449. Jackson also describes the acylation of a silylated 
cephalosporin nucleus in U.S. Pat. No. 3,694,437. German 
Offenlegungsschriff 2522997 (Derwent 81950W/50) discloses 
7-(D-.alpha.-hydroxyphenylacetamido)- 3-(6-hydroxypyridazin-3-yl or 
tetrazolo[4,5-b]-pyridazin-6-yl)thiomethyl- 3-cephem-4-carboxylic acid 
compounds which are protected on the .alpha.-hydroxyl and carboxylic acid 
functions. The silylated compounds are merely mentioned as incidental 
intermediates to the final products. Their preparation or properties are 
not expressly described in the disclosure. 
Cefamandole or its sodium salt in crude form are extremely difficult to 
purify by recrystallization. Therefore, a practical method of purification 
is necessary to provide the purity required for pharmaceutical 
preparations. Crystalline sodium cefamandole can be obtained from 
cefamandole acid provided the acid is in a pure state. 
The use of silyl groups as protecting groups which can be easily removed is 
widely recognized in the art. However, silylated cephalosporin compounds 
are generally so unstable that relatively few of them have been 
characterized as such. 
It is a purpose of this invention to provide a stable crystalline 
cefamandole silyl derivative which is readily converted to cefamandole 
acid of excellent purity. By the process of this invention crude lots of 
cefamandole can be converted to the silyl derivative or the silyl 
derivative can be prepared ab initio by silylation of the cephalosporin 
tetrazole nucleus followed by acylation with anhydro O-carboxymandelic 
acid. 
The reagents used in the processes of this invention are either 
commercially available or described in the literature. Both 
N-trimethylsilylacetamide (MSA) and N,O-bis(trimethylsilyl)acetamide (BSA) 
are commercially available. The preparation of the acylating agent 
D-anhydro-O-carboxymandelic acid, 
##STR1## 
is described by Greene in U.S. Pat. No. 3,840,531, Example V. 
SUMMARY OF THE INVENTION 
This invention is concerned with the process for the preparation of 
bis-trimethylsilyl cefamandole represented by Formula I 
##STR2## 
which comprises reacting 
7-amino-3-(1-methyl-1,2,3,4-tetrazol-5-yl)thiomethyl- 
3-cephem-4-carboxylic acid with a silylating agent selected from 
N-trimethylsilylacetamide, N,O-bis(trimethylsilyl)acetamide, 
N,O-bis(trimethylsilyl)trifluoroacetamide, 
N-trimethylsilyl-N-methyltrifluoroacetamide or N-trimethylsilylimidazole 
and acylating the product so formed with D-anhydro O-carboxymandelic acid 
in substantially anhydrous ethyl acetate. 
It is a further object of this invention to provide a process for the 
purification of crude cefamandole which comprises the steps of 
A. reacting 7-(D-mandelamido)-3-(1-methyl-1,2,3,4 
-tetrazol-5-yl)-3-cephem-4-carboxylic acid with a silylating agent 
selected from N-trimethylsilylacetamide, 
N,O-bis-(trimethylsilyl)acetamide, 
N,O-bis(trimethylsilyl)trifluoroacetamide, 
N-trimethylsilyl-N-methyltrifluoroacetamide or N-trimethylsilylimidazole 
in substantially anhydrous ethyl acetate to provide trimethylsilyl 
7-[D-(O-trimethylsilyl)mandelamido]-3-(1-methyl-1,2,3,4tetrazol-5-yl)thiom 
ethyl-3 -cephem-4-carboxylate; and 
B. reacting said silylated compound with a) water admixed with ethanol or 
isopropanol or b) isopropanol admixed with a primary alcohol selected from 
methanol, ethanol, propanol or butanol to provide 
7-(D-mandelamido)-3-(1-methyl- 
1,2,3,4-tetrazol-5-yl)thiomethyl-3-cephem-4-carboxylic acid isopropyl 
solvate and reacting said isopropyl solvate with water; and recovering 
said cefamandole as a hydrate. The primary hydrolysis product of 
bis-trimethylsilyl cefamandole is a metastable pentahydrate which is 
readily converted to the more stable trihydrate. 
The cefamandole hydrate can be readily converted to sodium cefamandole of 
excellent purity by reaction with sodium 2-ethylhexanoate or sodium 
acetate.

DETAIL DESCRIPTION AND PREFERRED EMBODIMENTS 
According to the process of this invention crude cefamandole can be 
silylated to provide bis-trimethylsilyl cefamandole (Formula I), 
hereinafter named BTMS-cefamandole, by reaction with silylating agents 
selected from the following group: 
N-trimethylsilylacetamide (MSA), 
N,o-bis(trimethylsilyl)acetamide (BSA), 
N,o-bis(trimethylsilyl)trifluoroacetamide (BSTA), 
N-trimethylsilyl-N-methyltrifluoroacetamide or 
N-trimethylsilyl imidazole (TMSI). 
The use of silylating agents which produce bases as by-products such as 
hexamethyldisilazane should be avoided because they cause undesirable 
isomerization of the cephalosporin .DELTA..sup.3 double bond. The 
silylated acetamide reagents produce neutral acetamide by-products and 
therefore they are preferred. Especially preferred for silylating 
cefamandole in the process of this invention are MSA and BSA. Two 
trimethylsilyl equivalents are required to silylate both the hydroxyl and 
carboxyl functions of cefamandole. Therefore, two molar equivalents of MSA 
and one molar equivalent of BSA are sufficient for complete silylation of 
cefamandole when the reagents are in a pure state. However, it has been 
found that an excess of silylating agent is preferred to provide 
crystalline BTMS-cefamandole in good yields when the reagents are of 
commercial grade quality. Therefore, it is desirable to react cefamandole 
with a two fold excess or at least 4 molar equivalents of commerical grade 
MSA. Usually one molar equivalent or a slight excess of commercial grade 
BSA is satisfactory for efficient silylation, the BSA being of better 
quality than MSA apparently. 
The silylation can be carried out at ambient temperature in a substantially 
anhydrous inert solvent such as ethyl acetate. By substantially anhydrous 
is meant that only trace amounts of water are permitted which will not 
materially affect the primary reaction. Ethyl acetate is preferred as a 
solvent because BTMS-cefamandole is only slightly soluble in said solvent, 
precipitates as a crystalline product from the reaction mixture, and is 
easily recovered by filtration. Unreacted materials and silylated 
impurities remain in the solvent solution. Because of the unique 
hydrophobic character of BMTS-cefamandole which renders it stable to water 
the acetamide by-product which often coprecipitates with the product is 
conveniently separated by washing with water. The silylation reaction is 
exothermic and when carried out at ambient temperature the temperature of 
the reaction mixture rises to about 40.degree. C. Although the reaction 
can be carried out at temperatures between 0.degree. and 80.degree. C. 
ambient temperature is preferred. The formation of BTMS-cefamandole 
product is rapid at ambient temperature and usually the product begins to 
precipitate within minutes of the addition of the reagents. Preferably the 
reaction is completed within two hours but longer reaction times can be 
used, although no improvement in yields accrues thereby. The quality of 
the BTMS-cefamandole obtained by the process described above is of 
sufficient purity for conversion to crystalline cefamandole. However 
BTMS-cefamandole can be recrystallized from ethyl acetate neat or from 
chloroform or methylene chloride by precipitation with n-hexane if it is 
desired or necessary to separate other organic impurities. 
BTMS-Cefamandole can be prepared ab initio from tetrazole nucleus by first 
silylating the nucleus and then acylating with D-anhydro O-carboxymandelic 
acid in substantially anhydrous ethyl acetate. Two trimethylsilyl 
equivalents are required for complete silylation of the nucleus to provide 
trimethylsilyl 7-trimethylsilylamino-3 
-(1-methyl-1,2,3,4-tetrazol-5-yl)thiomethyl-3-cephem-4-carboxylate in 
situ. Two molar equivalents of MSA or one equivalent of BSA or a slight 
excess thereof are preferred for silylation of the nucleus. With 
commercial grade MSA four molar equivalents are preferred for silylation. 
The silylation reaction proceeds rapidly at ambient temperature and the 
tetrazole nucleus goes into solution. Upon solution of the primary 
reactants the silylated nucleus is acylated preferrably with one molar 
equivalent or slight excess thereof of D-anhydro O-carboxymandelic acid. 
The acylation can be carried out by adding the silylated nucleus to the 
acylating agent or adding the acylating agent to the silylated nucleus. As 
the acylation proceeds the BTMS-cefamandole product precipitates out of 
solution and can be recovered by filtration. A unique result of the 
process is that the silylated product is obtained as a crystalline 
material which is stable to moisture and can be stored for propitious 
conversion to cefamandole pentahydrate or trihydrate as the case may be. 
The reaction conditions for the preparation of BTMS-cefamandole ab initio 
are analogous to those for the preparation from cefamandole as described 
hereinabove. The reactant ratios can be desirably varied according to the 
purpose, purity and cost of the reagents. For example excess silylating 
agent can be used to react with trace amounts of water in the reaction 
solvent. Recognizing that the cephalosporin reactant is the most expensive 
component, it is preferrable to use suitable excesses of the silylating or 
acylating reagents for more efficient conversion. 
The BTMS-cefamandole obtained by either of the methods described above can 
be converted to cefamandole by hydrolysis. Alternatively BTMS-cefamandole 
can be converted by solvolysis to an isopropyl solvate which in turn can 
be hydrolyzed to cefamandole under very mild conditions. In either case 
cefamandole pentahydrate is recovered as the primary product of the 
hydrolysis. However, cefamandole pentahydrate is a metastable material 
which can be easily converted to the more stable trihydrate form upon 
heating or prolonged drying. Therefore, it is more convenient to simply 
convert the hydrolysis product to cefamandole trihydrate by drying. 
Since BTMS-cefamandole is virtually insoluble in water, aqueous solvent 
mixtures are preferred for the hydrolysis. The silyl compound can be 
reacted with water admixed with ethanol or isopropanol. The hydrolysis can 
be best accomplished by heating the silyl compound in said solvent 
mixtures at the boiling temperature. Once solution of the silyl compound 
is achieved by heating, hydrolysis occurs at a rapid rate and is completed 
in a short time, usually within minutes. The pentahydrate compound can be 
recovered by evaporation of the solvents in vacuo or crystallization from 
solution by cooling. Upon drying the pentahydrate is converted to the more 
stable cefamandole trihydrate. 
BTMS-Cefamandole can also be reacted with isopropanol admixed with a 
primary alcohol selected from methanol, ethanol, propanol or butanol to 
form an isopropyl solvate. Cefamandole isopropyl solvate is readily 
hydrolyzed to cefamandole by reaction with cold water. Again the 
hydrolysis product can be recovered as cefamandole pentahydrate which upon 
drying is converted to the trihydrate. 
The following examples further illustrate the intermediates, compounds and 
processes of this invention. 
EXAMPLE 1 
Bis-Trimethylsilyl Cefamandole via Cefamandole 
7-(D-Mandelamido)-3-(1-methyl-1,2,3,4-tetrazol-5-yl)thiomethyl-3-cephem-4-c 
arboxylic acid, 4.0 g (8.6 mmoles), 5.4 g (34.4 mmoles) of 
N-trimethylsilylacetamide, and 50 ml of ethyl acetate were stirred for 2 
hours at room temperature. The precipitated product was filtered and dried 
in vacuo. The crude product was washed with water, dried and 
recrystallized from a mixture of chloroform and n-hexane to yield 3.3 g 
(63.5 percent) of trimethylsilyl 
7-[D-O-(trimethylsilyl)mandelamido]-3-(1-methyl-1,2,3,4-tetrazol-5-yl)thio 
methyl-3-cephem-4-carboxylate. 
Analysis C.sub.24 H.sub.34 N.sub.6 O.sub.5 S.sub.2 Si.sub.2 MW 606. 
Calcd: C, 47.55; H, 5.65; N, 13.87; S, 10.58. Found: C, 47.73; H, 5.40; N, 
14.02; S, 10.86. 
EXAMPLE 2 
Bis-Trimethylsilyl Cefamandole via Tetrazole Nucleus 
In this example the acylating agent is added to the silylated tetrazole 
nucleus. 
Eight grams (24.4 mmoles) of 
7-amino-3-(1-methyl-1,2,3,4-tetrazol-5-yl)thiomethyl-3-cephem-4-carboxylic 
acid, 12.8 g (97.6 mmoles) of N-trimethylsilylacetamide, and 100 ml of 
ethyl acetate were stirred at room temperature until the reactants 
dissolved. D-anhydro O-carboxymandelic acid, 4.77 g (26.8 mmoles), as a 
solution in ethyl acetate was added to the stirred reaction mixture. The 
reaction was stirred for 2 hours and seeded with trimethylsilyl 
cefamandole (Example 1). The product precipitated from solution and was 
filtered. The crude product was washed with water to remove acetamide and 
dried. The product was recrystallized from a mixture of methylene chloride 
and n-hexane to yield trimethylsilyl 
7-[D-(O-trimethylsilyl)mandelamido]3-(1-methyl-1,2,3,4-tetrazol-5-yl)thiom 
ethyl-3-cephem-4-carboxylate. 
Analysis C.sub.24 H.sub.34 N.sub.6 O.sub.5 S.sub.2 Si.sub.2 MW 606 
Calcd: C, 47.55; H, 5.65; N, 13.87; N, 10.43. Found: C, 46.12; H, 5.22; N, 
13.89; N, 10.58. 
EXAMPLE 3 
Cefamandole Isopropyl Solvate 
Trimethylsilyl 
7-[D-(O-trimethylsilyl)mandelamido]-3-(1-methyl-1,2,3,4-tetrazol-5-yl)thio 
methyl-3-cephem-4-carboxylate, 23.2 g, was dissolved in 75 ml of ethanol by 
boiling. The homogeneous solution was diluted with 500 ml of isopropanol 
and allowed to cool. The solution was concentrated in vacuo. The residue 
was dissolved in 250 ml of isopropanol, filtered and cooled to yield 14.85 
g of 
7-(D-mandelamido)-3-(1-methyl-1,2,3,4-tetrazol-5-yl)thiomethyl-3-cephem-4- 
carboxylic acid isopropyl solvate after filtration. A sample of the product 
gave an NMR spectrum consistent with the isopropyl solvate of cefamandole. 
EXAMPLE 4 
Cefamandole Pentahydrate 
One gram of trimethylsilyl 
7-[D-(O-trimethylsilyl)mandelamido]-3-(1-methyl-1,2,3,4-tetrazol-5-yl)thio 
methyl-3-cephem-4-carboxylate was dissolved in aqueous ethanol (2 ml of 
water, 25 ml ethanol) by boiling and heating for 10 minutes. The solution 
was diluted with 50 ml of water and cooled. The product crystallized to 
yield 0.9 g of 
7-(D-mandelamido)-3-(1-methyl-1,2,3,4-tetrazol-5-yl)thiomethyl-3-cephem-4- 
carboxylic acid pentahydrate. A sample of the product gave an NMR spectrum 
(deuteroacetone) consistent with cefamandole pentahydrate and indicating 
the absence of the trimethylsilyl groups. 
EXAMPLE 5 
Bis-Trimethylsilyl Cefamandole via BSA 
Four hundred and fifty four grams (0.98 mole) of cefamandole acid was added 
to a solution of 219.79 (1.08 moles) of N,O-bis(trimethylsilyl)acetamide 
(BSA) in 2300 ml of ethyl acetate. Within a few minutes the silyl 
derivative began to crystallize from solution. The mixture was stirred for 
about 2 hours. The insoluble product was filtered to yield 412.2 g (69.4 
percent) of trimethylsilyl 
7-[D-(O-trimethylsilyl)mandelamido]-3-(1-methyl-1,2,3,4-tetrazol-5-yl)thio 
methyl-3-cephem-4-carboxylate. 
EXAMPLE 6 
Bis-Trimethylsilyl Cefamandole via Silylated Tetrazole Nucleus 
In this example the tetrazole nucleus is first silylated and then added to 
the acylating agent. Eight grams (24.4 mmoles) of tetrazole nucleus, 
7-amino-3-(1-methyl-1,2,3,4-tetrazol-5-yl)thiomethyl-3-cephem-4-carboxylic 
acid, were reacted with 12.8 g (97.6 mmoles) of N-trimethylsilylacetamide 
in 45 ml of ethyl acetate at 60.degree. C until solution occurred. The 
mixture was allowed to cool to room temperature. The solution of silylated 
nucleus was added to 2.82 g (15.8 mmoles) of D-anhydro O-carboxymandelic 
acid in 35 ml of ethyl acetate at ambient temperature and stirred for 2 
hours. The insoluble product was filtered and dried in vacuo. The silyl 
product was washed in 300 ml of water to remove acetamide. The material 
was dried to yield 7.4 g of trimethylsilyl 
7-[D-(O-trimethylsilyl)mandelamido]3-(1-methyl-1,2,3,4-tetrazol-5-yl)thiom 
ethyl-3-cephem-4-carboxylate. 
EXAMPLE 7 
Conversion of Cefamandole Isopropyl Solvate to Cefamandole Trihydrate 
Cefamandole isopropyl solvate (Ex. 3), 3.85 g, was stirred for 1 hour with 
a mixture of water (300 ml) and ice. The insoluble product was filtered 
and dried in vacuo to yield 3.1 g of material. A sample of the product was 
subjected to X-ray powder analysis. The X-ray pattern was identical to 
that of an authentic sample of cefamandole trihydrate. 
EXAMPLE 8 
Bis-Trimethyl Cefamandole via N-(Trimethylsilyl)imidazole 
Ten millimoles (4.62 g) of 
7-(D-mandelamido)-3-(1-methyl-1,2,3,4-tetrazol-5-yl)thiomethyl-3-cephem-4- 
carboxylic acid were added to a solution of ethyl acetate (25 ml) and 4 ml 
(3.0 mmoles) of N-(trimethylsilyl imidazole. Upon solution of the 
reactants the product began to precipitate. The mixture was stirred for an 
hour. The insoluble product was filtered and washed with ethyl acetate and 
ether. The product was dried in vacuo to yield 6.06 g (45 percent) of 
trimethylsilyl 
7-[D-O-(trimethylsilyl)mandelamido]-3-(1-methyl-1,2,3,4-tetrazol-5-yl)thio 
methyl-3-cephem-4-carboxylate. A sample of the product gave an NMR spectrum 
identical to the spectrum of BTMS-cefamandole which was obtained by the 
method of Example 1. 
EXAMPLE 9 
Bis-Trimethyl Cefamandole via N,O-bis(Trimethylsilyl)trifluoroacetamide 
Two and one half grams (5.4 mmoles) of 
7-(D-mandelamido)-3-(1-methyl-1,2,3,4-tetrazol-5-yl)thiomethyl-3-cephem-4- 
carboxylic acid were added to a mixture of ethyl acetate (15 ml) and 3.5 ml 
of N,O-bis(trimethylsilyl)trifluoroacetamide. The mixture was stirred for 
2 hours. The precipitated product was filtered and dried in vacuo to yield 
2.0 g (61 percent) of trimethylsilyl 7-[D-O-(trimethylsilyl) 
mandelamido]-3-(1-methyl-1,2,3,4-tetrazol-5-yl 
thiomethyl-3-cephem-4-carboxylic acid. A sample of the product gave an NMR 
spectrum identical to the spectrum of BTMS-cefamandole which was obtained 
by the method of Example 1.