Name | Paclitaxel |
Synonyms | taxal taxol a PACLITAXEL Paclitaxel PACLITAXOL Paclitaxelx Paclitaxel HCL PACLITAXEL, TAXUS SPECIES Paclitaxel(natural crude) PACLITAXEL, TAXUS BREVIFOLIA N-BENZYL-BETA-PHENYLISOSERINE ESTER 7,11-methano-5h-cyclodeca[3,4]benz[1,2-b]oxete benzenepropanoic acid deriv. |
CAS | 33069-62-4 |
EINECS | 608-826-9 |
InChI | InChI=1/C47H51NO14/c1-25-31(60-43(56)36(52)35(28-16-10-7-11-17-28)48-41(54)29-18-12-8-13-19-29)23-47(57)40(61-42(55)30-20-14-9-15-21-30)38-45(6,32(51)22-33-46(38,24-58-33)62-27(3)50)39(53)37(59-26(2)49)34(25)44(47,4)5/h7-21,31-33,35-38,40,51-52,57H,22-24H2,1-6H3,(H,48,54)/t31?,32-,33+,35?,36?,37+,38?,40?,45+,46-,47+/m0/s1 |
InChIKey | RCINICONZNJXQF-MZXODVADSA-N |
Molecular Formula | C47H51NO14 |
Molar Mass | 853.92 |
Density | 0.200 |
Melting Point | 213°C (dec.)(lit.) |
Boling Point | 774.66°C (rough estimate) |
Specific Rotation(α) | D20 -49° (methanol) |
Flash Point | 9℃ |
Water Solubility | 0.3mg/L(37 ºC) |
Solubility | Insoluble in water, easily soluble in chloroform, acetone and other organic solvents. |
Vapor Presure | 0mmHg at 25°C |
Appearance | White crystalline powder |
Color | white |
Maximum wavelength(λmax) | 227nm(MeOH)(lit.) |
Merck | 14,6982 |
BRN | 1420457 |
pKa | 11.90±0.20(Predicted) |
Storage Condition | 2-8°C |
Stability | Stable. Incompatible with strong oxidizing agents. Combustible. |
Refractive Index | -49 ° (C=1, MeOH) |
MDL | MFCD00869953 |
Physical and Chemical Properties | Melting Point: 213-216°C |
Use | Broad-spectrum antineoplastic plant medicine for the treatment of ovarian cancer, breast cancer and other diseases |
Hazard Symbols | Xn - Harmful |
Risk Codes | R37/38 - Irritating to respiratory system and skin. R41 - Risk of serious damage to eyes R42/43 - May cause sensitization by inhalation and skin contact. R62 - Possible risk of impaired fertility R68 - Possible risk of irreversible effects R40 - Limited evidence of a carcinogenic effect R48 - Danger of serious damage to health by prolonged exposure R20/21/22 - Harmful by inhalation, in contact with skin and if swallowed. R68/20/21/22 - |
Safety Description | S22 - Do not breathe dust. S26 - In case of contact with eyes, rinse immediately with plenty of water and seek medical advice. S36/37/39 - Wear suitable protective clothing, gloves and eye/face protection. S45 - In case of accident or if you feel unwell, seek medical advice immediately (show the label whenever possible.) |
UN IDs | 1544 |
WGK Germany | 3 |
RTECS | DA8340700 |
FLUKA BRAND F CODES | 10-21 |
HS Code | 29329990 |
Hazard Class | 6.1(b) |
Packing Group | III |
Toxicity | LD50 intraperitoneal in mouse: 128mg/kg |
Taxol is a monomeric diterpenoid extracted from the bark of Taxus, which is a complex secondary metabolite, it is also the only known drug that can promote the polymerization of microtubules and stabilize the polymerized microtubules. Isotopic tracing indicates that paclitaxel binds only to polymerized microtubules and does not react with unpolymerized tubulin dimers. After exposure to paclitaxel, cells accumulate a large number of microtubules in the cell. The accumulation of these microtubules interferes with the various functions of the cell, especially the cell division stops in the mitotic phase, blocks the normal division of cells. Through Ⅱ-Ⅲ clinical research, paclitaxel is mainly applied to ovarian cancer and breast cancer, and has certain curative effect on lung cancer, colorectal cancer, melanoma, head and neck cancer, lymphoma and brain tumor.
The treatment of ovarian cancer and platinum-resistant ovarian cancer, breast cancer has a good effect on the treatment of prostate cancer, head and neck cancer, esophageal cancer, germ cell tumors, endometrial cancer, lymphoma, bladder cancer, upper gastrointestinal cancer, small cell and non-small cell lung cancer have good prospects.
The appearance was white crystalline or amorphous powder. It was first isolated from Taxus brevis by American chemist Wall et al. In1967. It can bind to tubulin and promote tubulin polymerization to assemble into microtubule dimer, thus inhibiting cell microtubule depolymerization and preventing cell rapid reproduction. Clinical trials have shown that paclitaxel has a significant effect in the treatment of metastatic ovarian cancer and breast cancer, and also has a certain effect in the treatment of small cell and non-small cell lung cancer, cervical cancer, anti-chemotherapy leukemia and so on. Taxol only exists in the genus Taxus, a total of 11 species, China has 4 species and 1 variety, they are TAXUS yunnanensis, Tibet TAXUS (also known as Himalaya), taxus chinensis, taxus chinensis var. Mairei (also known as Taxus chinensis). In addition to Taxol, these plants also contain a variety of other taxane diterpenes.
There are three methods for producing paclitaxel. The first is a synthetic method, the second is a bacterial culture method, and the third is a direct separation from Taxus. Although the first two methods have achieved significant research results, they have not achieved industrialization. At present, the separation from natural or cultivated Taxus is still the main way to produce Taxol. The separation process is generally methanol or ethanol leaching (or ultra-off boundary extraction) a hexane de-esterification of dichloromethane or chloroform extraction of crude extract a multiple silica gel column chromatography preparative HPLC, TLC, HSCCC was purified and recrystallized to give the product. Since it is difficult to separate paclitaxel from another derivative Cephal omanmne by silica gel column chromatography and the product yield is low, Kingston et al. used 03 to selectively oxidize Olefinic Bonds in Cepha-lomannine molecules, and then purified paclitaxel by silica gel column chromatography. In recent years, great progress has been made in the decolorization and separation of crude extracts of Taxus chinensis by using polymer resin, which overcomes the problems of low yield, small yield, high cost and long growth cycle of the original separation methods.
can be used for the treatment of metastatic ovarian cancer and breast cancer; Also for the treatment of small cell and non-cell lung cancer, cervical cancer, anti-chemotherapy leukemia and so on.
docetaxel is a potent inhibitor of bone marrow activity derived from the yew tree. Blood cell and platelet counts are monitored during treatment. The mechanism of action of the drug is similar to that of paclitaxel, which inhibits the depolymerization of microtubules and inhibits cell division. Treatment of advanced or metastatic breast cancer and non-small cell lung cancer by intravenous infusion.
Jiangsu Red Bean Group has invested tens of millions of yuan three or four years ago to build the largest Taxus chinensis fast-growing forest base in east China, with a total area of 7400 mu, and received high praise from the relevant departments of the United Nations and the leaders of the domestic Forestry Department. It is expected that the Red Bean Group will start production of paclitaxel raw material and injection this year, and design an annual output of 6 million paclitaxel injections. The project has passed the acceptance of the National Drug Inspection Bureau and the provincial and municipal drug administration.
In addition, China's Northeast forest area and some mountainous areas in Yunnan and Guizhou provinces are also vigorously developing TAXUS fast-growing forest cultivation techniques. In the next 3 to 5 years, these places are expected to form new TAXUS forest areas, so as to provide a valuable new source of paclitaxel raw material in China. Hunan, Hubei and other southern mountainous provinces are also building TAXUS cultivation bases, as one of the measures to help local farmers out of poverty and become rich. According to this development trend, the annual production of paclitaxel in China is expected to exceed 100 in the next few years, thus becoming the world's major producer of paclitaxel raw materials and preparations.
needle-like crystals or amorphous powders were precipitated from methanol. Melting Point 213~216 °c (decomposition). [Α] D20-49 ° (methanol). UV absorption maximum (methanol):227,273nm(& epsilon;29800,1700).
a. Infrared absorption: The main absorption band in the infrared spectrum is consistent with the control.
B. HPLC identification: in the content detection, the retention time of the main peak in the chromatogram prepared by the detection is consistent with the retention time of the main peak in the standard preparation chromatogram.
Purity: 99-100%, based on dry product without water and solvent.
Related Substances: total related substances ≤ 2.0%
Organic volatile impurities: meet the requirements of the United States Pharmacopoeia (USP) and Chinese Pharmacopoeia (CP) organic volatile impurities.
Specific rotation:[α]20 D =-49.0 ° ~ 55.0 °(10mg/mL methanol solution), based on dry product without water and solvent.
Moisture: ≤ 4.0%
Residue: ≤ 0.2%.
This includes a. Extraction to obtain an extract containing Taxol using TAXUS as a raw material; B. Removal of pectin and removal of colloid impurities in the extract; And c. Separation and purification.
The bark of Taxus chinensis is crushed (the finer the better),85% ~ 95% alcohol (what is the ratio of material to liquid?) 35-55 ° C hot reflux extraction three times (how much time is needed each time?), 50-70 ℃ vacuum decompression concentration to heat specific gravity 1.1~1.2g/ml, chloroform extraction, extract concentration into paste, paclitaxel content 1% chloroform paste, the paclitaxel content of 1% chloroform paste and chloroform dissolved completely, and silica gel stirred evenly, cool dry, sieved, filled into the column, chloroform-methanol gradient elution, TLC detection, segment combined concentration, the semi-finished product with paclitaxel content of 5-8% was prepared. The semi-finished product with paclitaxel content of 5-8% was completely dissolved by adding acetone, mixed with silica gel, dried, sieved, and filled into the chromatography column, acetone-petroleum ether gradient elution, TLC detection, combined and concentrated, paclitaxel content of 20 ~ 25% semi-finished products, with acetone-petroleum ether system crystallization 3~4 times, Suction filtration, 50 ℃ vacuum drying under reduced pressure, the semi-finished product with paclitaxel content of 75-80% was obtained. The product with paclitaxel content ≥ 99.5% was obtained by 16Mpa pressure chromatography, TLC detection, fractional merging and concentration.
The high-pressure silica gel column chromatography removes the colloid, and simultaneously, the taxane compound is separated into paclitaxel, cephalomannine, and 7-epipaclitaxel 3 fractions.
chromatographic conditions and system suitability test using eighteen alkyl silane bonded silica gel as filler; Methanol-water-acetonitrile (23:41:36) as mobile phase, the detection wavelength was 227nm. The system applicable solution 10 & micro;l under related substances shall be injected into the liquid chromatograph, and the separation degree of paclitaxel peak from paclitaxel impurity A peak and impurity B peak shall be greater than 1.0.
standard sample of paclitaxel (manufactured by Guizhou di-da), about 12mg, precision weighing, add 100ml measuring flask, add acetonitrile to dissolve and dilute to the scale, shake, 10 & micro;l was injected into the liquid chromatograph for precise measurement, and the chromatogram was recorded. According to the external standard method to calculate the peak area, that is.
This product is natural extraction or semi-synthetic preparation. This product is (2S,5R,7S,10R,13s)-10, 20-bis (acetyloxy)-2-benzoyloxy -1, 7-dihydroxy-9-oxo-5, 20-epoxytaxane -11-ene -13-YL (3S)-3-benzoylamino-3-phenyl-d-lactate. The content of C47H51NO14 shall be 98.0% ~ 102.0% calculated as dry product.
overview | paclitaxel is a monomeric diterpenoid extracted from the bark of the natural plant Taxus genus. it is a complex secondary metabolite and the only drug known so far that can promote microtubule polymerization and stabilize polymerized microtubules. Isotope tracing showed that paclitaxel only bound to the polymerized microtubules and did not react with the unpolymerized tubulin dimer. After contacting paclitaxel, cells will accumulate a large number of microtubules in the cell. The accumulation of these microtubules interferes with various functions of the cell, especially the cell division stops in the mitotic phase and blocks the normal division of the cell. Through Ⅱ-Ⅲ clinical research, paclitaxel is mainly suitable for ovarian cancer and breast cancer, and has certain curative effect on lung cancer, colorectal cancer, melanoma, head and neck cancer, lymphoma and brain tumor. |
indication | treatment of ovarian cancer and platinum-resistant refractory ovarian cancer and breast cancer has a good effect, and has a good prospect for the treatment of prostate cancer, head and neck cancer, esophageal cancer, germ cell tumor, endometrial cancer, lymphoma, bladder cancer, upper gastrointestinal cancer, small cell and non-small cell lung cancer. |
small history | In 1963, American chemists M.C. Wani and Monre E. Wall first isolated a crude extract of paclitaxel from the bark and wood of a Pacific fir (Pacific Yew) growing in the great forest of western United States. In the screening experiment of Taxus chinensis, Wani and Wall found that the crude extract of paclitaxel had high activity on in vitro cultured mouse tumor cells, and began to isolate this active ingredient. Due to the extremely low content of the active ingredient in plants, it was not until 1971 that they cooperated with Andre T. McPhail, a professor of chemistry at Duke University, to determine the active ingredient through x-ray analysis The chemical structure-a tetricyclic diterpene compound, and named it taxol. Taxol was discovered in Taxus chinensis in 1971 and found a unique anti-cancer mechanism. In 1992, the U.S. government transferred the patent to Squibb, and paclitaxel was introduced. In 1994, paclitaxel created the world's global sales champion of anti-cancer drugs. In 2000, the sales volume of paclitaxel reached 10 billion (the supply of raw materials did not increase further). In 2002, the central government issued a document prohibiting the cutting of wild yew and encouraging artificial planting. In 2004, Squibb's patent expired, and more pharmaceutical companies around the world were involved in the production of paclitaxel. In 2004, Huayuan began to operate the yew project and set up a directly affiliated paclitaxel refining and processing plant, with the goal of becoming the largest yew base in China and even Asia. In 2005, the central government issued a document again to conduct a national census of yew resources and encourage planting. In 2005, this project accepted investment from individual investors. |
method for efficient separation and purification of paclitaxel | it includes a, extraction, using yew as raw material to obtain an extract containing paclitaxel; B, remove colloid, remove colloid impurities in the extract; C. separation and purification. It is characterized in that the production process of paclitaxel is as follows: yew bark is crushed (the finer the better),85% ~ 95% alcohol (what is the ratio of solid to liquid?)35-55 ℃ hot reflux leaching three times (how long does it take each time?),50-70 ℃ vacuum decompression concentration to thermal specific gravity of 1.1~1.2 g/ml, chloroform extraction, extraction liquid concentration into paste, to obtain paclitaxel content of 1% chloroform paste, paclitaxel content of 1% chloroform paste with chloroform dissolved completely, add silica gel to stir evenly, cool and dry, sieve, fill into chromatography column, chloroform-methanol gradient elution, TLC detection, segmented concentration, to obtain paclitaxel content of 5 ~ 8% semi-finished products, the semi-finished product with paclitaxel content of 5-8% is completely dissolved with acetone, silica gel is added and stirred evenly, cooled and dried, sieved, and filled into a chromatography column. Acetone-petroleum ether gradient elution, TLC detection, segmented combination and concentration are carried out to obtain semi-finished product with paclitaxel content of 20-25%, crystallized with acetone-petroleum ether system for 3-4 times, filtered by suction, vacuum decompression drying at 50 ℃ to obtain semi-finished product with paclitaxel content of 75-80%, which is, TLC detection, segmented consolidation and concentration, target segment concentrate acetone-petroleum ether crystallization, suction filtration, drying, to obtain taxol content ≥ 99.5% finished products; The process of removing colloid is: high pressure silica gel chromatography column chromatography to remove colloid, and at the same time separate taxane compounds into paclitaxel, harringtonine, 7-table paclitaxel 3 parts. |
docetaxel | docetaxel is a very strong bone marrow activity inhibitor drug extracted from yew tree. blood cell and platelet count must be monitored during treatment. The mechanism of action of the drug is similar to that of paclitaxel, that is, it inhibits the depolymerization of microtubules and inhibits cell division. Treatment of advanced or metastatic breast and non-small cell lung cancer by intravenous infusion. |
international market analysis | so far, there are only two kinds of paclitaxel raw materials in the international market: one is from the bark of various yew; The other is to extract "10-berylatin" from European ornamental yew branches and then semi-synthesize it, the structure of docetaxel (docetaxel) is very similar to that of naturally extracted paclitaxel. These two APIs are best-selling APIs in the international pharmaceutical market, and have been in short supply for a long time. According to estimates by relevant departments, the sales ratio of paclitaxel APIs to docetaxel APIs is about 10:1. In the United States, paclitaxel injection (trade name: Paclitaxel) is mainly produced exclusively by Bristol-Myers Squibb. Currently, about two or three pharmaceutical companies produce paclitaxel raw materials and preparations, but the market is basically monopolized by Bristol-Myers Squibb. The total sales of paclitaxel preparations produced by several other companies are only a fraction of Bristol-Myers Squibb. Docetaxel APIs and preparations are mainly produced by France's Planck company, Britain, Italy and other companies, with Planck's largest output. Paclitaxel is the preferred anti-tumor drug in hospitals all over the world. In recent years, the incidence of tumors in various countries in the world has nearly doubled compared with 10 years ago. Malignant tumors such as lung cancer, breast cancer and ovarian cancer are also showing a frequent trend. These cancer patients are the main users of paclitaxel. On the whole, sales of paclitaxel will only rise, not fall, until no new plant-based anti-cancer drug can take its place. According to the latest figures released by the World Health Organization, the United States has now become the world's number one cancer-prone country, with 1.4 million new cancer cases each year, accounting for about 14% of the world's cancer patients that year. The United States is still the largest consumer of paclitaxel. With the increasing incidence of cancer in the United States, paclitaxel, as the main drug against advanced malignant tumors, can be believed that its sales will continue to maintain a rapid upward trend. The United States and other developed countries have already summarized a set of optimal compatibility schemes for paclitaxel and other anti-cancer drugs in the course of clinical use for more than ten years. Its medical department is inseparable from the "backbone" of paclitaxel. Therefore, the demand for paclitaxel raw materials will also rise. |
domestic situation | Jiangsu hongdou group has invested tens of millions of yuan to build the largest fast-growing yew forest base in east China three or four years ago, with a total area of 7400 mu. the artificially cultivated yew seedlings have long been lulled into forests and have been highly praised by the relevant departments of the United Nations and the leaders of the domestic forestry department. It is expected that Hongdou Group will start production of paclitaxel raw materials and injections this year, with an annual output of 6 million paclitaxel injections. The project has passed the acceptance of the State Drug Administration and the provincial and municipal drug administrations. In addition, my country's northeastern forest areas and some mountainous areas in Yunnan and Guizhou provinces are also vigorously developing fast-growing yew forest cultivation techniques. In the next 3 to 5 years, these places are expected to form new yew forest areas, thereby providing valuable products for the country New sources of paclitaxel raw materials. Hunan, Hubei and other southern mountainous provinces are also building yew cultivation bases as one of the measures to help local farmers get rid of poverty and become rich. According to this development trend, the annual output of paclitaxel raw materials in China is expected to exceed 100kg in the next few years, thus becoming the world's major producer of paclitaxel raw materials and preparations. |
precautions for injection | 1. hematological toxicity: as the main factor limiting the increase of dose, G-CSF should be used to assist when white blood cells are lower than 1500/mm3, and blood components should be transfused when platelets are lower than 30,000/mm3. 2. Allergic reaction: In addition to pretreatment, if there are only mild symptoms such as flushing, skin reaction, slightly faster heart rate and slightly lower blood pressure, it is not necessary to stop the drug, and the drip speed can be slowed down. However, if there are serious reactions such as low blood pressure, angioedema, dyspnea, and systemic measles, the drug should be stopped and given appropriate treatment. Patients with severe allergies should not be treated with paclitaxel again next time. 3. Nervous system: The most common is numbness of fingers and toes. About 4% of patients, especially at high doses, may have obvious sensory and motor disorders and reduced tendon reflexes. There have been individual reports of grand epileptic seizures during instillation. 4. Cardiovascular: transient tachycardia and hypotension are more common and generally do not need to be treated. However, it should be closely observed in the first hour of instillation, except for patients with severe conduction block, it is not necessary to observe every hour. 5. Joints and muscles: About half of the patients will feel joint and muscle pain 2 to 3 days after medication, which is related to the dosage used. It usually recovers within a few days. Muscle pain will worsen in patients given G-CSF. 6. Hepatobiliary system: Since most of the paclitaxel is excreted from bile, patients with hepatobiliary diseases should be observed with caution. In thousands of cases, about 8% of patients had elevated bilirubin, 23% of patients had elevated alkaline phosphatase, and 18% had elevated aspartate aminotransferase. However, there is no data to show that paclitaxel has serious damage to liver function. 7. Other: Although gastrointestinal reactions are common but generally not serious, a few may have diarrhea and mucositis. Mild alopecia is also more common. |
chemical properties | needle crystal or amorphous powder is precipitated from methanol. Melting point 213~216 ℃ (decomposition). [α]D20-49 ° (methanol). UV maximum absorption (methanol):227,273nm(ε 29800,1700). |
use | broad-spectrum anti-tumor botanicals for ovarian cancer, breast cancer, etc. broad-spectrum anti-tumor botanical drugs, used to treat ovarian cancer, breast cancer and other diseases anti-tumor drugs. For the treatment of metastatic breast cancer and metastatic ovarian cancer. Broad-spectrum anti-tumor botanical drugs for the treatment of ovarian cancer, breast cancer and other diseases effective anti-tumor drugs; combined with the N-terminal region of β-tubulin, it promotes a highly stable microtubule formation, Resist depolymerization, prevent normal cell division and capture in the G2 / M phase of the cell cycle. An anti-microtubule drug that inhibits depolymerization by promoting tubulin polymerization, maintains tubulin stability, and inhibits cell mitosis. On human endothelial cells, IC50 is 0.1 pM. |
production method | natural products separated and purified from yew bark, woody roots, leaves, twigs and seedlings, with the highest content in bark. The scientific name of Taxus in the Botany of China is Taxus, and the plant classification belongs to the gymnosperm subphylum, Pinus, Taxus, Taxus. Taxus family contains 5 genera and 23 species. There are 4 genera, 12 species and 1 variety in China, namely Tibetan Taxus wallichinanaZucc or Himalayan Taxus, Taxus yunnanensis, Taxus chinensis vat.Mairei and Taxus cuspidata. Distributed in Tibet, Yunnan, Guizhou, Sichuan, Guangxi, Guangdong, Hunan, Hubei, Jiangxi, Fujian, Zhejiang, Anhui, Henan, Shanxi, Shaanxi, Gansu and Jilin mountainous areas. Extracted from the bark or leaves of Taxus plants. Taxus bark or leaves are dried in the shade, ground, and extracted with 95% ethanol. The extract is concentrated to dry, and the remainder is mixed with water and dichloromethane. The organic layer is separated from the rest, and the water layer is extracted with dichloromethane many times. After the extract and the organic layer are combined, they are concentrated to dryness. The residue is dissolved in ethyl acetate-methanol (3:1), mixed with fresh diatomite, and then evaporated to remove the solvent under reduced pressure. The remaining powder was subjected to rapid column chromatography, first washed with hexane, and then eluted with dichloromethane. The latter is collected and the dichloromethane is steamed under reduced pressure. The residue is dissolved in ethyl acetate, and 70 sets (3-4 sets per set) of medium-pressure rapid chromatographic columns with silica gel are used for chromatography, and different ratios of hexane-acetone are used for elution. Collect the components containing the product and concentrate it. The residue is then purified by a medium-pressure rapid chromatographic column filled with silica gel, and eluted with different ratios of methanol-dichloromethane. Collect the components containing the product and concentrate them under reduced pressure. The residue is then separated by a preparative high performance liquid chromatography, and the obtained product is recrystallized twice with aqueous methanol to obtain pure paclitaxel. Yield: bark 0.028%, leaves 0.0088%. Yield: bark 93.3%, leaves 88%. Melting point 212~214 ℃,[α]D20-49 (1%, chloroform). The stem bark of Taxus chinensis was crushed, dried in the shade, soaked in 1% citric acid aqueous solution for 24 hours and then began to percolate. The percolate is extracted with dichloromethane, the extract is dried, concentrated, and vacuum drained. Second column chromatography was performed with silica gel, and the collected effluent contained paclitaxel and harringtonine. Based on their different side chain structures, dissolve them in carbon tetrachloride and add bromine, only brominate harringtonine, and then undergo silica gel column chromatography to obtain an effluent containing only paclitaxel. After treatment, the taxol is obtained with a 99.19% content, a yield of 4.5 × 10-5, and a recovery rate of 70%. |
EPA chemical information | The information is: ofmpub.epa.gov provides (external link) |
toxic substance data | The information is: pubchem.ncbi.nlm.nih.gov Provide (external link) |