Oxytetracycline powder is a light yellow to yellow brown crystalline powder with a polymorphic crystal structure. Molecular formula C22H24N2O9, CAS 79-57-2. Studies have shown that oxytetracycline exists in multiple crystal forms (such as alpha and beta), and there are differences in solubility, dissolution rate, and bioavailability among different crystal forms. For example, the alpha form has slightly higher solubility in water than the beta form, but their stability under acidic conditions is similar. The crystalline morphology (such as needle like or flake like) affects its fluidity and compressibility. In the production of formulations, it is necessary to optimize the crystallization process (such as solvent selection and temperature control) to obtain suitable crystal forms, in order to ensure that the tablet hardness and dissolution meet the standards. Degradation may occur at high temperatures, producing degradation products with nephrotoxicity. Commonly used to treat various infectious diseases caused by sensitive bacteria, such as respiratory infections such as pneumonia and bronchitis, urinary system infections such as cystitis and pyelonephritis, intestinal infections such as bacterial dysentery and amoebic enteritis, skin and soft tissue infections such as cellulitis and abscesses, and eye infections such as trachoma and conjunctivitis.
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Oxytetracycline +. COA
Solubility and pH dependence
The solubility of oxytetracycline shows a significant pH dependence, and its solubility curve follows a "U" - shaped distribution:
Acidic conditions (pH<3):
The solubility significantly increases, reaching 10-20 mg/mL (such as a solubility of 15 mg/mL in 0.1N HCl).
Neutral conditions (pH 6-8):
Extremely low solubility (<0.5 mg/mL), prone to precipitation.
Alkaline conditions (pH>9):
The solubility slightly increases, but the drug is prone to hydrolysis reactions, resulting in the formation of ineffective 4-isomer.
Clinical significance:
Formulation design:
Oral formulations should be avoided from being used in combination with antacids (such as sodium bicarbonate) to prevent a decrease in absorption due to an increase in gastric pH.
Injection compatibility:
When intravenous infusion, a separate route is required to avoid mixing with solutions containing calcium and magnesium ions (such as Ringer's solution) to prevent the formation of insoluble chelates.
Localized medication:
Eye ointment (3% concentration) needs to be adjusted to pH 4.5-5.5 to balance drug solubility and eye irritation.
Acid base bisexuality and salt formation
Oxytetracycline powder molecules contain phenolic hydroxyl groups (pKa ₁=3.27) and enol hydroxyl groups (pKa ₂=7.32), exhibiting acid-base amphiphilic behavior
Acidic environment: Reacts with alkali to produce sodium salts (such as sodium oxytetracycline), with solubility increased to over 100 mg/mL, suitable for injection.
Alkaline environment: reacts with acid to form hydrochloride salt (such as oxytetracycline hydrochloride), with a solubility of 50 mg/mL, commonly used in oral preparations.
Stability difference:
Sodium oxytetracycline: Stable in alkaline solution, but easily decomposed when exposed to light, and needs to be stored away from light.
Oxytetracycline hydrochloride: Stable in acidic solution, but may precipitate crystals after long-term storage, and the storage temperature needs to be controlled (2-8 ℃).
Application scenarios:
Animal premix: using oxytetracycline calcium salt to reduce the absorption rate of the drug in the gastrointestinal tract, prolong the action time, and reduce tissue residue.
Long acting injection: Prolonged drug half-life and reduced dosing frequency through esterification modification (such as palmitate).
Oxytetracycline is a broad-spectrum tetracycline antibiotic, which is mainly synthesized through microbial fermentation. Chemical synthesis methods are less commonly used in industry due to their high cost and complex steps. The following systematically elaborates on the synthesis pathway and key technologies of oxytetracycline from four dimensions: microbial fermentation, chemical synthesis, semi synthesis, and modern biotechnology optimization.
Microbial fermentation method: the core path of industrial production
Microbial fermentation is the mainstream technology for the industrial production of oxytetracycline, and its core is to utilize the metabolic capacity of Streptomyces rimosus or Streptomyces aureofaciens to achieve efficient synthesis by optimizing fermentation conditions.
High yield strain screening: Streptomyces strains are isolated from soil and induced to mutate using ultraviolet radiation, chemical mutagens (such as nitrosoguanidine), or gene editing techniques (such as CRISPR-Cas9) to screen for high-yielding tetracycline producing mutant strains. For example, after mutagenesis, the production of oxytetracycline powder in Streptomyces sp. M528 increased by 30%.
Culture preservation technology: Adopting inclined low-temperature preservation method (4 ℃ refrigerator preservation for 3 months), sand tube preservation method (dry sand mixed and sterilized, preservation period of 1-10 years), vacuum freeze-drying method (rapid freezing below -15 ℃, vacuum sublimation of water, preservation period of 5-15 years), to ensure the stability of culture activity.
Carbon source selection: Starch and dextrin are the main sources, while glucose is prone to metabolic inhibition and needs to be added at a controlled amount (usually<5%). For example, in a certain process, the amount of starch used in a fermentation tank reaches 546kg/10m ³, accounting for over 90% of the total carbon source.
Nitrogen source regulation: Organic nitrogen sources such as soybean cake powder and corn syrup are used in combination with inorganic nitrogen sources such as ammonium sulfate to promote bacterial growth and antibiotic synthesis. Add 1.74kg/500L ammonium sulfate to the three-stage fermentation tank, and control the nitrogen source concentration at 0.03% -0.05%.
Mineral salt addition: Calcium carbonate (1.39kg/500L) adjusts pH, sodium chloride (1.74kg/500L) maintains osmotic pressure, and potassium dihydrogen sulfate (10.49g/500L) provides phosphorus source.
Use of defoamer: a large amount of foam is produced during fermentation, and vegetable oil (such as soybean oil 1L/500L) or foam enemy (polyether defoamer) should be added to control the height of foam.
Temperature segmented management: The three-stage fermentation tank adopts temperature control in stages of 30-31 ℃: from 0-50 hours, 31 ℃ promotes bacterial growth, from 51-150 hours, 30 ℃ optimizes metabolic pathways, and from 151 hours to 151 hours, the temperature rises to 31 ℃ to accelerate product release.
PH dynamic adjustment: During the initial stage of fermentation, the pH is controlled between 6.3-6.5 and maintained by adding ammonia water; After 100 hours, the pH drops to 6.2-6.3, promoting the synthesis of oxytetracycline; Stop ammonia injection 8 hours before placing the can to avoid product degradation.
Dissolved oxygen and stirring: A tubular heat exchanger and stirring blade (speed 100-150rpm) are used to increase dissolved oxygen, with a ventilation rate of 0.5-1.0vvm (air volume per cubic meter of fermentation broth per minute) to ensure aerobic demand.
Feeding strategy: Add starch fermentation solution based on residual sugar value (4g/L residual sugar control before 100 hours) to avoid bacterial autolysis caused by carbon source depletion; Simultaneously supplementing nitrogen sources such as ammonium sulfate to maintain metabolic balance.
Total fermentation time: 160-200 hours (about 7-8 days), bacterial biomass reaches 20-30g/L, and oxytetracycline potency is 8000-10000u/ml.
Product distribution: After fermentation, about 70% of oxytetracycline is deposited in the mycelium, and 30% is present in the fermentation broth, which needs to be released through acidification treatment.
Chemical synthesis method: a technical pathway for laboratory research
The chemical synthesis method constructs the molecular structure of oxytetracycline powder through multiple organic reactions, but due to the cumbersome steps and high cost, it is only used for laboratory research or structural modification.
Using penicillin G potassium salt as raw material, tetracycline parent nucleus was constructed through oxidation, ring expansion, ring opening and other reactions. For example, the potassium salt of penicillin G reacts with trichloroethyl chloroformate in the presence of pyridine to form the intermediate trichloroethyl ester, which is then oxidized by hydrogen peroxide to obtain penicillin sulfoxide.
Ring expansion reaction: Sulfopenicillin undergoes C-C bond cleavage and recombination after treatment with phosphoric acid, forming a 12 membered ring of oxytetracycline core.
Functional group introduction: Introducing functional groups such as dimethylamino (C4 position) and hydroxyl (C5, C6 position) through acylation, oxidation, and other reactions. For example, the C6 hydroxyl group is introduced through selective oxidation reaction, and the reaction conditions need to be controlled to avoid excessive oxidation.
Differential Isomer Control: Under acidic conditions (pH 2-6), the C4 dimethylamino group is prone to undergo differential isomerization, resulting in the formation of 4-differential oxytetracycline without antibacterial activity. It is necessary to suppress isomerization by controlling pH (>6) or adding stabilizers (such as citric acid).
Solvent extraction: Use ethyl acetate or methanol to extract oxytetracycline, and transfer the product to the organic phase by adjusting the pH (8.5-9.0).
Crystallization process: Add concentrated hydrochloric acid to the organic phase and heat it to 40-60 ℃. Oxytetracycline hydrochloride crystallizes and precipitates. After washing and drying, the pure product is obtained.
Semi synthetic method: optimization path for structural modification
The semi synthetic method uses natural oxytetracycline as the raw material and improves its physicochemical properties or antibacterial activity through chemical modification. The typical representative is the synthesis of deoxytetracycline (doxycycline).
C6 deoxygenation modification:
Under acidic conditions (such as 50% sulfuric acid, heated at 50 ℃), oxytetracycline undergoes dehydration of its C6 hydroxyl group to produce deoxytetracycline. The product has a 50 fold increase in lipid solubility, an oral absorption rate of 95%, an extended half-life of 18 hours, and a 10 fold increase in antibacterial activity.
Differential isomer inhibition:
The C5 hydroxyl group of tetracycline forms an intramolecular hydrogen bond with the C4 dimethylamino group, which stabilizes the alpha configuration and reduces isomerization. Further enhance hydrogen bonding and improve product stability through structural modifications, such as introducing fluorine atoms.
Optimization of Modern Biotechnology: Frontier Exploration of Synthetic Biology
With the development of synthetic biology, gene editing and metabolic engineering have been applied to optimize the biosynthetic pathway of oxytetracycline.
Cloning and Expression of Gene Clusters
Clone the oxytetracycline biosynthesis gene cluster (approximately 30kb) from Streptomyces fissilis, introduce it into Escherichia coli or yeast, and construct a heterologous expression system. For example, expressing the polyketide synthase gene (otcY) in Escherichia coli to achieve the synthesis of tetracycline precursor substances.
Metabolic pathway regulation
By knocking out competitive pathway genes (such as genes encoding secondary metabolites) or overexpressing key enzyme genes (such as polyketide synthase genes), the production of oxytetracycline powder can be increased. For example, overexpression of the otcB gene (encoding malonyl CoA carboxylase) increased tetracycline production by 40%.
Intelligent fermentation process
By combining online monitoring (such as pH, dissolved oxygen, and residual sugar sensors) with feedback control systems, fermentation parameters can be adjusted in real-time. For example, when the dissolved oxygen is below 20%, the stirring speed or ventilation rate is automatically increased to ensure the metabolic needs of the bacterial cells.
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