JPS6045879B2 - New penicillins and their production methods - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to novel penicillin derivatives and methods for their production.

First, the novel penicillin derivative which is the object of the present invention has the formula: However, in formula (1), R is a hydrogen atom or a hydroxyl group that may be acylated, and -COOR'' is a carboxyl group that may be esterified. These pharmaceutically acceptable salts or hydrates thereof are also included within the scope of the present invention.

More specifically, R in formula (1) is a hydrogen atom,
or a hydroxyl group that may be acylated, such as a free hydroxyl group or its acetate, propionate, butyrate, fluoroate, benzoate, methyl carbonate, ethyl carbonate, propyl carbonate, butyl carbonate esters, etc. In addition, the optionally esterified carboxyl group represented by 1COOR'' refers to a free carboxyl group; or its alkali metal salts such as sodium, potassium, etc.; organic amine salts such as triethylamine and diisopropylamine; methyl, Ethyl, benzyl, acetoxymethyl, α-
Acetoxyethyl, pivaloyloxymethyl, α-ethoxycarbonyloxymethyl, α-methoxycarbonyloxymethyl, α-methoxycarbonyloxyethyl,
．． These are esters such as benzhydryl, 1-indanyl, phthalidyl, dimethylaminoethyl, and trimethylsilyl. Compound (1), which is the object of the present invention, has excellent antibacterial activity against a wide range of pathogenic bacteria such as Gram-negative bacteria and Gram-positive bacteria, including Pseudomonas aeruginosa, and is a useful compound as a medicine.

The novel penicillin derivatives targeted by the present invention can be synthesized according to the following method.

(1) Compound (1) can be obtained by reacting a compound having the formula: (R, R'' are as defined above) with a compound having the formula: or a reactive derivative thereof.

Compounds used as raw materials in this method (■)
can be obtained by obtaining a compound of the formula: from a compound having the formula:, silylating this new compound, and then phosgenating the compound.

(Ii) A penicillin derivative (1) which is an object of the present invention can be obtained by reacting a compound of the formula: (R'' is the same as above) with a compound of the formula: (R is the same as above) or a reactive derivative thereof. can be obtained.

Here, the compound (■) is the compound (■) with the formula: (Xθ
is a halogen ion).

The novel compounds (■), (■), and (■) used in the production of the objective compound (1) of the present invention are of course not only important as synthetic intermediates for the objective compound (1), but also for other pharmaceuticals, It is also a useful compound as a synthetic intermediate for agricultural chemicals.

Furthermore, the new compound (■) is also an important compound as a synthetic intermediate for other antibiotics, antitumor peptides, etc. less than,
The method for producing the novel penicillin derivative of the present invention will be explained in more detail.

First, the raw material compound (■), for example, 1-benzalimino-2-oxoimidazolidone (■
) can be easily produced by steam distillation under sulfuric acid.

The reaction formula is as follows. Isolation and purification of this compound (■) can be carried out according to conventional methods.

The starting compound (■) is a new compound and can be synthesized by the following three methods.

(However, M is sodium or potassium, and X is a halogen atom.) In method (a), compound (■) is
, 3-dithiolane-2-thione without solvent, 80
This is carried out by heating at ~150°C until the generation of hydrogen sulfide stops, and the following purification is carried out by a conventional method.

In method (b), S-methyl-1,3-dithiolane-2-thione-halide (iodide) obtained by reacting 1,3-dithiolane-2-thione with an alkyl halide, generally methyl iodide, and compound (■) are combined. , in a suitable organic solvent such as methanol, ethanol, dimethylformamide, dimethylacetamide, acetonitrile, etc., at -10 to 80°C, and after confirming the completion of the reaction by thin layer chromatography, the reaction is carried out using a conventional method. Perform separation and purification.

In method (c), compound (■) is reacted with carbon disulfide in the presence of alkali hydroxide, and further halogenated ethylene (e.g. ethylene bromide, ethylene chloride) or a derivative thereof is added to give a reaction mixture of 50 to 100%. 'C to react.

Isolation and purification are then carried out according to conventional methods. Furthermore, the compound (■)
As a method for producing the reactive derivative (■)'', the following example can be cited as one that is excellent in both quality and yield.

That is, the silylating agent used in this reaction is preferably trimethylsilyl chloride, hexamethyldisilazane, bistrimethylsilylacetamide, or the like. After silylation, the new compound (■)'' can be easily obtained by contacting the product with phosgene or a phosgene precursor dissolved in an organic solvent such as tetrahydrofuran or dioxane. Although it can be recrystallized from an inert organic solvent, the above reaction can yield a product of such high purity that it can be used in the next reaction without purification. Further, compound (■)'' can be easily produced by reacting the above-mentioned compound (■) and compound (X) in an appropriate solvent in the presence of an acid absorbing agent.

Examples of the solvent used here include water, tetrahydrofuran, dioxane, acetone, dimethylformamide, dimethylacetamide, acetonitrile, or a mixed solvent thereof. On the other hand, as the deoxidizing agent, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, triethylamine, pyridine, dimethylaniline, etc. can be used. Reaction temperature is -10~5
0°C, and the compound (■) thus obtained is isolated and purified according to known methods. Furthermore, the compound of formula (■) is commercially available as ampicillin, amoxicillin, or a derivative thereof.

The novel penicillin derivative of the present invention can be produced by, for example, reacting (1) compound (■) with compound (■), or (Ii
) Compound (■) and compound (■) can be reacted.

First, in (1), compound (■) such as sodium, potassium, triethylamine, pyridine, dimethylaniline salt or silylated product and compound (■) are mixed with water,
It consists of reacting in a solvent such as ether, tetrahydrofuran, dioxane, acetone, acetonitrile, dimethylformamide, methylene chloride or mixtures thereof under low temperature conditions, generally at temperatures in the range -50 to 30C.

The products thus obtained are known in the art. Isolate and purify according to method.

Next, in (Ii), the compound (■) synthesized as described above and the compound (V) are condensed.

In this case, reactive derivatives of compound (■) are generally used. Examples of the reactive derivatives include acids. light,
Mixed acid anhydrides, active esters, etc. are used. In addition, when using free carboxylic acid as it is, it is necessary to use an appropriate condensation reagent, such as N,
N''-dicyclohexylcarbodiimide, N,N''-carbonylimidazole, phosphorus oxychloride, Vilsmeier's reagent, etc. are used. Such a reaction is well known in the fields of penicillin chemistry and peptide chemistry. These reactions are usually carried out in a suitable solvent such as methane dichloride, chloroform, tetrahydrofuran, dioxane,
It is carried out in dimethylformamide, dimethylacetamide, acetonitrile, acetone, dimethylsulfoxide, water or mixtures thereof.

The reaction temperature varies depending on the type of reactive derivative or condensation reagent, but is generally -50 to 30°C. Compound (1) thus obtained can be isolated and purified by a known method, and if necessary, it can be acylated in the case of a free hydroxyl group, and acylated in the case of a free carboxylic acid group, according to a known method. can also be converted into pharmaceutically acceptable salts or esters.

Thus, while the compound of formula (1) obtained according to the present invention has high antibacterial activity, it is not toxic at an effective dose (LD5O value when administered intravenously to mice is 5y/Kg or more). It is a compound useful as a medicine.

For example, the novel penicillin derivatives of the present invention exhibit excellent antibacterial activity against a wide range of pathogenic bacteria, Gram-negative and Gram-positive bacteria, including Pseudomonas aeruginosa. The penicillin derivative of the present invention can be administered to humans or animals in various administration forms, either orally or parenterally, and can be used alone or as a pharmaceutical agent. For example, tablets can be prepared by combining commonly used adjuvants, liquid diluents, binders, lubricants, humectants, etc.
Granules, sugar-coated tablets, powders, capsules, gels, syrups,
It is used in common pharmaceutical composition forms such as ampoules, suspensions, solutions, emulsions, tablets, pastes, creams, and suppositories.

Other additives that may be included include dissolution retardants, absorption enhancers, surfactants, etc., and any known pharmaceutically acceptable additives may be used.

The novel penicillin derivatives of the present invention can be used alone or as a mixture of two or more different derivatives as the active ingredient of the pharmaceutical composition, in an amount of about 0.1 to 99% by weight of the total pharmaceutical composition. .5%, preferably from about 0.5%
It is 95%.

The pharmaceutical composition of the present invention comprises, in addition to the novel penicillin derivative or mixture thereof, other pharmacologically active compounds.
It is also possible to mix them as active ingredients.

The daily dosage of the novel penicillin derivative of the present invention for patients depends on the type of animal, body weight, and treatment. Approximately 1 to 1000 m per 1 kg of body weight, although it varies depending on the desired condition.
9, preferably about 10-800 mg.

The present invention will be described in more detail below with reference to Examples. Reference Example 1: Production of Compound (■) When a mixed solution of 1-benzalimino-2-oxo-imidazoline 208f1 water 2e and concentrated sulfuric acid 125ml was subjected to steam distillation for 4 hours, the distillation of benzaldehyde almost stopped.

This reaction solution is filtered and extracted with chloroform. The solution is neutralized with sodium hydroxide and evaporated to dryness. The residue is extracted with chloroform 5e, and the chloroform is distilled off.
The obtained crude crystals are recrystallized from ethanol. Yield 62
y0 melting point 104-109 CIR (KBr) 1700c
m-1 (C=0) 3300c! n-1(
〉NH) 3400cm-1(-NII2
) NMR (D6-DMSOlOOrs/[Hz) δ3.
00-3.40 (4H, mCH2x2) 3.96 (21
(,S,-NH2)6.42(1H,s,>NH) Reference Example 2 Production of 1-(1,3-dithiolane-2-imino)-2-oxoimidazoline 1-Amino-2-oxoimidazoline 13. 7f- is dissolved in 30 ml of water, and a solution of 7.63' potassium hydroxide and 10 ml of water is added thereto.

12.4' of carbon disulfide was added dropwise to this for 1 hour. This mixture is stirred at room temperature for 1 hour and then at 45° C. for 5 hours. Next, excess carbon disulfide is distilled off under reduced pressure, a solution of 7.63 y of potassium hydroxide and 10 ml of water is added, and after stirring at room temperature, 25.6 f of ethylene bromide is added dropwise while cooling with water. Stir for 1 hour at room temperature. Water is added to the reaction solution in which crystals have precipitated, and the crystals are dissolved by heating. After washing by adding petroleum ether to this, it is extracted with chloroform and dried over anhydrous sodium sulfate. Next, the solvent is distilled off, and the residue is recrystallized from ethyl alcohol. Yield 9.8g, melting point 219-220℃
. IR (KBr) 1690cm-1 (C=0)
3260(1-77!-1(〉NH)MSm/e
:203 (M NMR (CDce3-D6DMSO4l
lOOMHz) δ3.18(21-[,SCH2)3.
28-3.56 (2H, mCH2) 3.50 (4H, sCH2x2) 6.72 (1H, sNH) Elemental analysis value C6H9ON3S2 CHN Actual value 35.714.4520.43 Calculated value 36.004.5020. 70 Reference Example 3 Production of 1-(1,3-dithiolane-2-imino)-2-oxoimidazolidine 3.03y of 1-amino-2-oxoimidazolidine and 3.407g of 1,3-dithiolane-2-thione were mixed. The mixture was heated and stirred for 3 hours in an oil bath at 110° C. in a nitrogen stream.

Add warm water to dissolve this, wash with a benzene-hexane mixture, and filter. Water is distilled off from the mustard liquor under reduced pressure, and the residue is recrystallized from ethanol. Yield 3.6g, melting point 21
9-220℃. Reference example 41-(1,3-dithiolane-2
Preparation of -imino)-2-oxo-imidazolidine 6.46 f of 1-amino-2-oxo-imidazolidine is dissolved in 50 mt of dimethylformamide.

Add 20 ml of triethylamine to this and cool to -5°C. While stirring this solution, 19.46 y of S-methyl-1,3-dithiolane-2-thione-iodide was added over 3 hours. After stirring at room temperature for 2 days, dimethylformamide is distilled off under reduced pressure. The residue is dissolved in water, washed with benzene, and then extracted with chloroform. After drying over anhydrous sodium sulfate, chloroform is distilled off. The residue is recrystallized from ethanol. Yield 6.8q1 Melting point 219~
220℃. Reference example 51-chlorocarbonyl-2-oxo-3-(1,3-dithiolane-2-imino)imidazoj
Preparation of Lysine A mixture of 3.5' of 1-(1,3-dithiolane-2-imine)-2-oxoimidazolidine and 7.4 ml of hexamethyldisilazane is heated under reflux in a nitrogen stream for 6 hours.

Next, excess hexamethyldisilazane is distilled off under reduced pressure. Add 50mt of tetrahydrofuran to this and dissolve it.
Phosgene is introduced for 5 hours at room temperature. Next, the reaction vessel is tightly stoppered and stirred overnight. The reaction solution is reduced in pressure to completely distill off volatile components. The desired crude crystal 4.89f was obtained. Melting point 103-107°C (decomposed). IR(KBr)1770
11712cIn-1 (C=0) Reference Example 6D-(-)-
α-([2-oxo-3-(1,3-dithiolane-2-
Preparation of D-(-)-1α-phenylglycine (2.57 f of imino)-imidazolidin-1-yl]monocarboxamido)-phenylacetic acid was dissolved in 10 ml of sodium hydroxide and 30 ml of water, and 10 ml of boh hydrochloric acid was added thereto to pH
7.6, and D-(-)-α-phenylglycine was precipitated in a finely dispersed form.

In this suspension, 1-chlorocarbonyl-2-oxo-3-
Add 4.89 V of crude crystals of (1,3-dithiolane-2-imino)-imidazolidine. While stirring the mixture, add △sodium monohydroxide to maintain the pH at 7.7.

Next, the solution is filtered and washed with chloroform, and then, while cooling on ice, diluted hydrochloric acid is added to adjust the pH to 2. Crystal 5.1f was obtained. Melting point 227-230°C. IR(KBr)165
0, 1730c "1 (C=O)
3325 cm-1 (>NH) MSm/e: 380 (M NMR (D6-DMSOlOOMHz) δ3.57 (8HmCH2×8) 5.28 (1H, s-NH) 7.30 (5H, s-C6H5) Element Analytical value CHN Actual value 46.704.1714.30 Calculated value 47.354.2414.73 Reference example 7 D-(1)-α-([2-oxo3-(1,3-dithiolane-2-imino)-imidazolidine- Preparation of 1-yl]monocarboxamide)-(4-hydroxyphenyl)monoacetic acid D-(1)-barahydroxyphenylglycine 4
．． Add and dissolve sodium hydroxide in a suspension of 676 g and 60 ml of water.

While vigorously stirring this solution, add HCl to pH 7.6.
shall be. To this suspension, 8.85 f of crude crystals of 1-chlorocarbonyl-2-oxo-3-(1,3-dithiolane-2-imino)-imidazolidine were added, and then sodium hydroxide was added to maintain the pH at 7.7. After 3 hours, the solution is filtered, and while cooling the solution on ice, the pH is adjusted to 2 with Beau hydrochloric acid. The precipitated crystals are separated and washed with water (the obtained crystals show 2 spots on thin layer chromatography).

This crude crystal was dissolved in 50 ml of 10% ammonia water,
After stirring for 5 hours, the mixture was washed with chloroform and filtered. Cool the liquid on ice and adjust the pH to 2 with hydrochloric acid. Separate the precipitated crystals, wash with water, and dry. 5.52 da of white crystals are obtained, showing a single spot on thin layer chromatography. Melting point 228-229°C. IR (KBr) 1720, 166
011608c! n-1 (C=0) 32
50~3300cm-1(〉NHOH)MS(FD)m
/E396(M+)NMR(CDC'3+D6DMSO
lOOMlI2p) δ3.55 (4H, sCH2×2
) 3.69 (4H, sCI1, x2) 5.25 (1H, α, J = 7 pressure Cα-H) 6.73x7.20 (4H, d, J = clear LC6H4)
8.78 (IH, d, J = 7 NH) Elemental analysis Cl
5Hl6N4O5S2 CHN Actual value 45.014.0214.10 Calculated value 45.454.0414.14 Example 1 6-(D-(1)-α-[(2-oxo 3-(1,3
-dithiolane-2-imino)-imidazolin-1-yl)-carboxamide]-α-phenylacetamide)-
Production of penicillanic acid Ampicillin trihydrate 3.227g
suspended in 60 ml of 80% aqueous tetrahydrofuran,
Add and dissolve the required minimum amount of triethylamine.

While cooling this on ice and stirring, 1-chlorocarbonyl-2
-Oxo-3-(1,3-dithiolane-2-imino)-
Add 2.425y of imidazolidine crude crystals little by little,
At the same time, triethylamine was added dropwise to pH 7. O~7.5
Keep it. After reacting for 1 hour, 100 ml of water was added to adjust the pH to 7, and the pressure was reduced to distill off tetrahydrofuran.

Next, the liquid was left overnight, cooled on ice, and diluted with bo-hydrochloric acid to pH 2.
shall be. The precipitated crystals are separated from P, washed with water, and dried in a vacuum desiccator. Yield 2.765y1 Melting point 148-153° C0IR (KBr) 177\172 to 16750-1 (
C=0) NMR (D6-DMSOlOOrl!4HZ)
δ1.40(3H,s,2-CH3)1.54(3H,
s2-CH3) 3.60 (8H, mCH2×4) 4.16 (1H, s3H) 7.32 (5H, sC6E5) 8.83 (1H, d, J=?eclipse NH) 9.22 (1H, d, J = clear NH) Elemental analysis value C23H26N6O6S3 CHN Actual value 47.354.6714.07 Calculated value 48.004.5014.50 Example 2 6(D-(-)-α-[(2-oxo3 -(1,3-dithiolane-2-imino)-imidazolidiwar-1-yl)monocarboxamide]-α-phenylacetamide)-
Preparation of penicillanic acidD-(-)-α-([2-oxo3-(1,3-dithiolane-2-imino)-imidazolidin-1-yl]carboxamido)-phenylacetic acid2.
Add 5 ml to 20 ml of anhydrous acetone, and add 0.9 ml of triethylamine and 0.013 ml of dimethylaminoethanol.
Add m1 and dissolve.

The solution was cooled to -30°C and 0.5% of methyl chloroformate was added.
Add 34ml. Then 6-aminopenicillanic acid 1.5
64f, 4.5mt of water, 6.3Tnt of acetone? Add a cooled solution of sodium monohydroxide to pH 8 while cooling with ice to the previous solution at once, stir at 0°C for 3 minutes, and then add 100 ml of water.
mL was added, and the acetone was distilled off under reduced pressure at 20°C. This solution was washed with 50 ml of chloroform, filtered, and adjusted to pH 2 with 2N hydrochloric acid while cooling on ice to precipitate white crystals. This is washed with water and dried in a vacuum desiccator. Yield 3.02q1 Melting point 150-155°C0 Example 36-(D-(-)-α-[(2-oxo 3-(
Preparation of 1,3-dithiolane-2-imino)-imidazolidin-1-yl)-carboxamide]-α-1(4-hydroxyphenyl)-acetamido)-penicillanic acid 2.097 V of amoxicillin trihydrate was suspended in 60 ml of 80% aqueous tetrahydrofuran. The mixture was made cloudy, and 1.593y of 1-chlorocarf-2-oxo-3-(1,3-dithiolane-2-imino)-imidazolidine was used to react in the same manner as in Example 7 to obtain 2.97y of the title compound.

Melting point: 175-185°C. 51R (KBr) 1770, 1
72011670CTf1-1 (C=0) NMR (D
6-DMSOlOOMHz) δ1.42 (3H,
s2-CH3) 1.56 (3H, s2-CH3) 3.60 (8H, mCII2×4) 1, 4
．． 16 (1H, s..3H) 6.68,7614
(4H, d, J = Sumise C6H4) 8.71 (1H
, d, J=81L7NH) 9.07(1H, dJ
=? Ox NH) Elemental analysis value C23H26N6O7S
3lCHN actual value 45.

564.4λ14.02 Calculated value 46.454.4114.13 Example 4 6-(D-(1)-α-[(2-oxo3-(1
, 3-dithiolane-2-imino)-imidazolidin-1-yl)-carboxamide]-α-1(4-acetoxyphenyl)-acetamido)-penicillanic acid 6-(D-(1)-α-[(2- Oxo 3-
(1,3-dithiolane-2-imino)-imidazolysin-1-yl)-carboxamide]-alpha-1(4-hydroxyphenyl)-acetamido)-penicillanic acid 1.7
83y, 25ml of water, 11N sodium monohydroxide 6ml
Add and dissolve.

While stirring this under ice-cooling, 1.674 g of acetic anhydride was added to 20
Add 1N sodium monohydroxide to maintain weak alkalinity during and after the dropwise addition. After 1 hour of filtration, the solution was adjusted to pH 2 with 2N monohydrochloric acid while cooling on ice to precipitate white crystals.

Wash with water and dry in a vacuum desiccator. Yield 1.
647f1 Melting point 160-165°C. IR(KBr)17
75s1720, 1670cm-1 (C=O)
1200C7F! -1NMR (Mountain-DMSO
lOOMHz) δ1.40 (3FI, s2-CH3) 1.
52 (3H, s12-CH3) 3.40-3.80 (8
H, mCH2×4) 4.20 (1H, s3-H) 5.3
2-5.78 (3FI, m, 5, 6αH) 7.10, 7
．． 42 (4H, d, J=?C6H4) 8.93 (1H,
d, J=? NH) 9.29 (1H, d, J=811$7
NH) Example 5 1-Ethoxycarbonyloxyethyl-6-(D-(-)-α-[2-oxo-3-(1,3-dithiolane-2-imino))-imidazolidin-1-yl)-carboxamide]-α- Preparation of (4-acetoxyphenyl)-acetamido)-penicillanate 6-(D
-(1)-α-[2-oxo-3-(1,3-dithiolane-2-imino)-imidazolidin-1-yl)-carboxamide]-α-(4-acetoxyphenyl)-acetamido)-penicillanic acid 1.46 Dissolve Da in 10 ml of dimethyl sulfoxide.

When 0.238y of potassium carbonate is added to this and stirred at room temperature, carbon dioxide gas is generated and the mixture becomes a potassium salt, becoming almost transparent. To this was added 100 mg of 18-crown-6 (crown ether manufactured by Nippon Soda), and further added 0.526 y of α-chlorodiethyl carbonate, and the mixture was stirred at room temperature for a specific time while passing nitrogen gas. This solution is poured into 100 ml of ice water and extracted with 150 ml of methylene chloride. The extract was washed twice with water, dried over anhydrous magnesium sulfate, and methylene chloride was distilled off. Ether is added to the residue to crystallize it, separated and dried. This is recrystallized from isopropanol. Yield 0
．． 9f1 melting point 120-127C0IR (KBr) 178
0,1760,1720,1680cm-1 (C=0)
1200C77! -1 NMR (D6-DMSOlOOMHz) δ1.00-1.64 (1211, m2-CH3X2
-CH2-9■, -CH-QI) 3.5-3.76 (8
H, mCH2×4) 4.15 (2H, q-q?-CH3
) 4.36 (1H, d3-H) 5.38-5.76 (3H, m, 5,6α-H) 6.5
8-6.80 (1H, m-0-CU-0-) 7.08,
7.

41 (4H, d, J = 81L7, C6H4) 8.90 (
1H, d, J = soaked BNH) 9.32 (1H, d, J = soaked LNH) Next, the minimum inhibitory concentration (
■C) was measured according to the standard method of the Japanese Society of Chemotherapy.

Claims (1)

[Claims] 1 Formula: ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (I) However,
A novel penicillin represented by the following formula, in which R is a hydrogen atom or a hydroxyl group that may be acylated, and -COOR' represents a carboxyl group that may be esterified. 2 Formula: ▲There are mathematical formulas, chemical formulas, tables, etc.▼(II) However, the formula (
In II), R is a hydrogen atom or a hydroxyl group that may be acylated, and -COOR' is a carboxyl group that may be esterified, and the formula: ▲ Numerical formula, chemical formula, table, etc. There are ▼ Formulas that are characterized by reacting with the compound represented by (IV) or its reactive derivative: ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (
I) A method for producing a novel penicillin, where R and R' are as defined above. 3 Formula: ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (V) However, in formula (V), -COOR' represents a carboxyl group that may be esterified. , tables, etc. ▼ (VI) However, in formula (VI), R represents a hydrogen atom or a hydroxyl group that may be acylated. Formula: ▲ Formula,
There are chemical formulas, tables, etc. ▼ (I) However, R, R'
is as defined above. A method for producing a novel penicillin.