Retinoic acid

Dermatology drugs

Retinoic acid（Tretinoin,302-79-4） is commonly used in dermatology drugs, which is the department of vitamin A (Victoria methanol) metabolic intermediates.It mainly affects the growth of bones and epithelial metabolism, can promote epithelial cell proliferation and updates, and can inhibit the proliferation and differentiation of keratinocytes, so hyperkeratosis can be back to normal. Therefore many complete or incomplete keratosis, hyperkeratosis of diseases have a certain therapeutic effect, treat a variety of skin diseases. The use of the drug can penetrate topical skin quickly, enable significantly increased epithelial cell turnover. This class of drugs has strong and rapid inhibition on the secretion of the sebaceous glands, can reduce sebum secretion. In addition, the product also has anti-tumor, promote wound healing and anti-inflammatory effects.

Clinical application

Retinoic acid(302-79-4) is mainly used in the treatment of psoriasis, ichthyosis, follicular keratosis, acne, lichen planus, verrucous epidermal nevus, impetigo, vitiligo, lichen psoriasis, the face of pityriasis alba, etc. In addition, the drugs also have some preventive effect on skin cancer.

Tretinoin Cream

Physicochemical property

Retinoic acid(302-79-4) is a yellow needle crystal, with a similar smell of vitamin acetate. Soluble in methanol, ethanol, acetone, chloroform, dichloromethane , also in vegetable oil and fatty. In case of light, it is thermal instability, suck up moisture in the air, polymerization and metamorphism in water. The melting point of all trans-vitamin A acid is 182~180°C, the melting range of which is mixed with a small amount of isomers is 170~190°C.

Tretinoin structure

Pharmacological action

Retinoic acid(302-79-4) can induce epidermal hyperplasia, and improve the granular layer and the cell layer thickness.It can influence the silk protein process and the formation of cross-linked film and promote the differentiation of epidermal granular layer cells in the late stage of the differentiation of the epidermal cells by affecting K10, K1 keratin solution. This product can significantly inhibit the formation of experimental acne, prevent and eliminate acne lesions. Tretinoin also affect melanocyte cell melanogenesis , it has more than a number of functional points, having inhibitory effect on the activity of Tyrosine hydroxylase, dopa oxidase and two hydroxyindole oxidase three catalyzing enzyme, so as to reduce the formation of melanin, reduce skin pigmentation. It has no effect on the normal black prime cellular tyrosinase activity and black pigment composition.

Pharmacodynamics

Tretinoin can increase the cell nucleus division and epidermal cell turnover, form of the stratum corneum cell adhesion, and easy to fall off. It can remove the existing acne, while inhibiting the formation of new acne, hair follicle epithelial replacement can prevent the blockage of the plug. The synthesis of keratin is also inhibited, which can affect the metabolism of epithelial cells. It has the effect of promoting the proliferation and differentiation of epithelial cells, and the dissolution of keratinocytes.

Pharmacokinetics

External use has a small amount of skin absorption, large area of application of the increase in absorption. About 5% of the amount of external use urine. This product is absorbed well, the blood can reach the concentration peak after 3 hours, blood concentration can reach 0.3~0.5mg/ml, after oral administration of 1 mg/kg. After oral absorption, it is widely combination with plasma protein and has half-life of 0.7 h in a mean elimination. After a single oral dose of 40mg, blood drug concentration can be up to the source metabolic level in 7~12 hours. Multiple oral administration has not seen in vivo accumulation, but the blood concentration of the drug is significantly decreased, which may be due to the induction of cytochrome P450 enzymes, and the elimination of the rate of increase and bioavailability. It mainly used in the liver metabolism, which is metabolites of glucose acid esters. 60% of metabolites is by renal excretion, and can also be excreted by bile but metabolite half-life is longer.

Vitamin A acid medicine

Vitamin A acid medicine is a kind of natural or synthetic existence with vitamin A activity of retinol (retinol) derivatives. The drug discovery is regarded as a new milepost for treatment of skin diseases and cosmetic pharmacology. In the last 20 years, the application of the dimension A acid has made great progress in the treatment of many skin diseases. So far, there have been 2500 retinoic acid derivatives. According to its development process and chemical structure, they can be divided into three generations: the first generation is class of non aromatic retinoid, tretinoin and isotretinoin as the representative. The second generation is class of single aromatic A acids, etretinate and acitretin as the representative; the third generation is class of aromatic dimensional A acid, aromatic methyl ethyl acetylene, adapalene and vitamin A acid ethyl ester as the represented.

use of of vitamin A in skin diseases

The indications

Used in the treatment of acne vulgaris, especially the blackhead acne lesions, senile, fluorescent or drug skin atrophy, ichthyosis and various abnormal keratinization and pigment excessive calm skin disease, and psoriasis.

Usage dosage

(1) ointment: use 0.1% ointment for the other skin lesions and 0.05% ointment for acne skin lesions in the topical application. Clean the skin with warm water after one time every night.
(2) gel: apply to the affected area. At the beginning of treatment , it can be taken one time every two days or every three days. Afterwards smear one time every night.

Adverse reaction

This product may cause skin irritation symptoms such as burning, erythema, swelling, desquamation, crusting, pigment increase or decrease, may make the skin lesions more obvious, but also showed that the drug is working, not aggravated illness. Most of the skin can be adapted and tolerated, the phenomenon can be gradually disappeared. If irritation persists or increased, you can take intermittent or suspended medication.

Precautions

(1) This drug is contraindicated in pregnant women and patients with the allergic to the Tretinoin, the A derivative of vitamin A, acute or subacute dermatitis, eczema, skin diseases.
(2) Allergic caution.
(3) Women should stop breastfeeding during the period of the nursing period. Women of childbearing age are prohibited during the period of pregnancy .Children with caution.
(4) The product should avoid contacting with eyes and other mucous membranes (e.g., mouth, nose, etc.). Do not use in skin of wrinkling location and skin ulceration.
(5) The site of using medicine, appearing the things such as burning, itching, redness, etc. should discontinue medication, and the local is washed clearly. Consult the doctor if necessary.
(6) For the treatment of acne, the first few weeks ache can be temporarily intensified, but should continue to treat more than 6 weeks to reach the maximum effect.
(7) The product should not be used in large areas, the daily dosage should not exceed 20g.
(8) During the course of medication, do not use other drugs ,which can cause irritation and damage to skin, cosmetics and cleaning agents, so as not to aggravate the skin reaction, resulting in increase in drug absorption and cause systemic adverse reactions.
(9) The sun can accelerate Tretinoin decomposition and stimulate heavier to the skin. Animal experiments suggest that Tretinoin can enhance the ability of ultraviolet radiation, so the product is most appropriate in the evening and bedtime application, the treatment process should avoid the sun, or the use of shading measures.

Drug interaction

(1)Retinoic acid combining with light sensitive drugs can increase the risk of photosensitiveness.
(2)Retinoic acid combining with soap and detergents, containing keratolytic agents (such as peroxy benzoic acid, Resorcinol, salicylic acid, sulfur,etc), ethanol preparation, isotretinoin can aggravate irritation or dryness to skin, and therefore must be used with caution.
(3) Retinoic acid combining with sago cimetidine, cyclosporine and diltiazem, verapamil and ketoconazole, can cause an increase in the blood concentration of the drug, and may lead to retinoic acid poisoning.
(4 Retinoic acid combining with pentobarbital, rifampicin, phenobarbital, can cause the blood concentration of the product decreasing.
(5) The product will affect the liver cytochrome P450 enzyme system, resulting in changes in blood concentrations of the drug.
(6)Taking drugs oryzanol, vitamin B1, vitamin B6 with Tretinoin, can make headache relieved or disappeared, because of adverse reactions of the drug.
There are Informations on Common tretinoin in the Department of Dermatology,incluing the pharmacological effects , pharmacokinetics, pharmacodynamics, indications, drug interactions, and adverse reaction of the drug, these were edited by Yuri Huang in the chemcialbook (2015-09-24).

Uses

(1) Applies to abnormal tyshiyongyupe of acne, fish phosphorus disease and abnormal psoriasis.
(2) Resistance to abnormal skin drugs.
(3) Tretinoin mainly affects the growth of bones and epithelial metabolism, can promote epithelial cell proliferation and updates, and can inhibit the proliferation and differentiation of keratinocytes, so hyperkeratosis can be back to normal. Therefore many complete or incomplete keratosis, hyperkeratosis of diseases have a certain therapeutic effect, treat a variety of skin diseases. Tretinoin is mainly used in the treatment of psoriasis, ichthyosis, follicular keratosis, acne, lichen planus, verrucous epidermal nevus, impetigo, vitiligo, lichen psoriasis, the face of pityriasis alba, etc.

Indications and Usage

Retinoic acid(302-79-4) is a commonly used dermatological drug and an intermediate product in bodily vitamin A (dimethyl alcohol) metabolism. It has a similar odor to that of vitamin A acetate. It is easily soluble in methanol, ethanol, acetone, chloroform, dichloromethane, and it is also soluble in vegetable oil and fats. It is instable when in contact with light and heat, hygroscopic in air, and polymerizes and metamorphosizes when in contact with water.
Retinoic acid also anti-tumor, wound-healing, and infection-resisting effects. It is mainly used clinically to treat psoriasis, hair follicle keratosis, acne, lichen planus, verrucous epidermis nevus, ureophora, vitiligo, pityriasis rosea, and facial pityriasis simplex, especially blackhead skin lesions, and senile, sun-induced, or drug induced skin atrophy, as well as various keratosis abnormalities and hyperpigmentation diseases. In addition, it also has certain preventative effects against skin cancer. Retinoic acid can significantly inhibit experimental acne breakouts.

Mechanisms of Action

Retinoic acid(302-79-4) mainly affects bone growth and epithelium metabolism, it can promote epithelium cell growth and renewal, and it can inhibit keratinocyte growth and differentiation to correct hyperkeratosis. Thus, it has certain curative effects on diseases related to keratinization, hypokeratinization and hyperkeratinization. A localized application can penetrate the skin very quickly and cause significant growth in epithelial cells. Retinoic acid has a strong and rapid inhibiting effect on sebaceous glands and can reduce sebum secretion. Retinoic acid promotes epidermal growth, thickens the stratum granulosum and stratum spinosum, and affects K1 and K10 keratinysis in late stage epidermal cell differentiation to influence the siloxin to silymeric protein process and cross-linked coating formation, thus promoting epidermal granulosa cells to differentiate towards the cuticle layer. It regulates follicular sebaceous gland epithelium keratinization abnormalities to remove keratin plugs, thus being able to prevent and remove acne lesions, and follicular epithelial renewal can also prevent keratin plugs and acne formation. In addition, retinoic acid can also affect melanogenesis of melanocytes with a multi-site effect, and it can inhibit the activity of tyrosine hydroxylase, dopa oxidase, dihydroxyl indole oxidase, and other type-three catalytic enzymes, thus lowering the formation of melanin and reducing hyperpigmentation. It has not impact on normal human melanocyte tyrosinase activity and melanin content.

Pharmacokinetics

A small amount is absorbed by the skin through external use, and absorption increases as application area increases. Approximately 5% of the externally applied amount is excreted through urine. This product is well-absorbed when taken orally and reaches peak blood concentration in 3 hours. With an oral dosage of 1mg/kg, blood concentration can reach 0.3-0.5 mg/ml. After oral absorption, it will bind universally with serum protein, and its average clearing half-life is 0.7 hours. After a single 40mg dose, blood concentration reaches its endogenous metabolism level in about 7-12 hours. Multiple oral doses do not appear to accumulate in the body, but blood concentration will noticeably decrease, possibly due to the induction of cytochrome P450, thus causing the clearing rate to increase and bioavailability to decrease. It is mainly metabolized in the liver, and its metabolite is esterified glucuronic acid. 60% of the drug is excreted by the kidneys, it can also be excreted through bile, and its metabolite’s half-life is longer than that of the drug itself.

Drug Interactions

• Combined use with light-sensitive drugs may increase the risk of light sensitivity.
• Use with caution when combined with soap and other detergents, preparations containing keratolytic (such as benzoyl peroxide, thalidomide, salicylic acid, and sulfur), preparations containing ethanol, or isotretinoin, as this may worsen skin irritation and dryness.
• Combined use with cimetidine, cyclosporine, diltiazem, verapamil and ketoconazole may increase the blood concentration of this drug and lead to retinoic acid poisoning.
• Combined use with pentobarbital, phenobarbital and rifampicin may decrease the blood concentration of this drug.
• This drug will impact the hepatic cytochrome P450 enzyme system and change the blood concentration of this drug.
• Taking oryzanol, vitamin B1 or vitamin B6 while also taking this drug may alleviate or eliminate adverse effects of this drug, including headaches.

Adverse reactions

May cause skin irritations such as a burning sensation, erythema, swelling, desquamation, scabbing, or change in pigmentation. May cause skin lesions to become more obvious, but this means that the drug is taking effect, and not that the condition is worsening. Mostly tolerated or tolerable on the skin, and irritation may subside gradually. If irritation continues or worsens, use periodically or cease use.

Warnings and Precautions

• Patients who are allergic to this drug or vitamin A derivatives, have acute or subacute dermatitis, have eczema or related skin diseases, and pregnant women should not use this drug.
• Use with caution if susceptible to allergies.
• Breastfeeding women should stop breastfeeding when using this drug, and women of childbearing age should not get pregnant when using this drug. Children should use with caution.
• Keep drug out of eyes and other mucosa (such as mouth and nose). Not suitable or skin folds and skin ulcerations.
• If the applied area experiences burning sensation, itching, or redness and swelling, stop use immediately, clean the applied area, and consult a physician if necessary.
• This drug is used to treat acne, and a couple weeks of use can prevent worsening, while continued use for over 6 weeks will have the best curative effect.
• This drug is not suitable use in large areas, and daily dosage should not exceed 20g.
• While using this drug, do not use any drugs, cosmetics, or cleansers that may irritate and damage the skin to prevent worsened skin reactions and adverse effect caused by increased drug absorption.
• Sunlight can increase retinoic acid’s irritation to skin and break down retinoic acid. Animal studies showed that retinoic acid can increase the carcinogenic ability of ultraviolet rays, so this drug is best used at night and before sleep. Avoid direct sunlight during treatment, or protect treated areas from sunlight.

Description

all-trans Retinoic acid is a metabolite of vitamin A and a ligand for retinoic acid receptors (RARs) with IC₅₀ values of 9, 3, and 10 nM for RARα, RARβ, and RARγ, respectively, in radioligand binding assays. It induces expression of a luciferase reporter in COS-7 cells expressing RARα, RARβ, or RARγ (EC₅₀s = 169, 9, and 2 nM, respectively). all-trans Retinoic acid (17 nmol) reduces papilloma formation induced by phorbol 12-myristate 13-acetate (TPA; ) in mice. It reduces bile duct proliferation, hydroxyproline levels, and liver inflammation in a rat model of α-naphthylisothiocyanate-induced chronic cholestasis and reduces plasma levels of alkaline phosphatase and bile salts in the Mdr2^-/- mouse model of cholestasis. all-trans Retinoic acid also reduces hepatic fat accumulation, triglycerides, body weight, and serum glucose levels in mice with Western diet-induced obesity.

Chemical Properties

Yellow-Orange Powder

Originator

Aberel,McNeil,US,1973

Uses

retinoic acid (tretinoin) is a vitamin A derivative. It has demonstrated an ability to alter collagen synthesis, increase dermal hyaluronic acid levels, and stimulate fibroblast growth and the extracellular matrix. It is used for keratinization disorders and for treating acne. Retinoic acid’s anti-aging effect has been convincingly documented and it is often used for treating the visible signs of aging, though these results can take approximately 6 months to be visible. It is associated with a number of adverse effects, including irritation, photosensitivity, skin dryness, redness, and peeling. It should also not be used while pregnant.

Uses

Physiological metabolite of vitamin A. Effects gene expression via nuclear retinoic acid receptors (RAR); mediates cellular growth and differentiation

Indications

Topical tretinoin (Retin-A, Renova, Avita), like isotretinoin, alters keratinization in the acroinfundibulum. In addition, it reverses certain premalignant and other histological changes associated with the photoaging changes that accompany chronic exposure to ultraviolet radiation. Topically applied tretinoin is indicated in comedogenic and papulopustular acne vulgaris, and its mild exfoliative effects make it sometimes useful in molluscum contagiosum, flat warts, and some ichthyotic disorders. It is often prescribed to lessen the clinical signs of photoaging (wrinkling and hyperpigmented macules).

Definition

ChEBI: Retinoic acid is a retinoid in which all four exocyclic double bonds have E- (trans-) geometry. It is a naturally occurring derivative of vitamin A (retinol). Retinoids such as tretinoin are important regulators of cell reproduction, proliferation, and differentiation and are used to treat acne and photodamaged skin and to manage keratinization disorders such as ichthyosis and keratosis follicularis.

Manufacturing Process

100 parts of beta-ionol are dissolved in 200 parts of dimethylforrnamide and after the addition of 165 parts of triphenylphosphine hydrobromide, stirred for 7 hours at room temperature. Then 70 parts of 4-methyl-1-al-hexadiene- (2,4)-acid-(6) (melting point 177°C, white needles from water) are added to the now clear solution. 150 parts of isopropanol are added and the whole cooled to -30°C. Into this solution, while stirring vigorously, 190 parts by volume of a 30% solution of sodium methylate in methanol are allowed to flow in. A vigorous exothermic reaction takes place and the temperature in the interior of the flask rises to +5°C. It is stirred for another 5 minutes and neutralized with 10% of sulfuric acid (until acid to Congo).
After stirring for 2 hours at room temperature, the mass of vitamin A acid has crystallized out. It is sharply filtered off by suction and washed with a little ice-cold isopropanol. From the filtrate, a further small amount of mainly all trans vitamin A acid crystallizes out upon the addition of water. The filter cake is suspended in 600 parts of water and stirred for 4 hours at room temperature; it is filtered by suction and the product washed with water. It is dried in vacuo at 40° to 50°C and 115 parts of vitamin A acid are obtained. The melting point lies between 146° and 159°C.
The mixture of the all trans and mainly 9,10-cis vitamin A acid may be separated by fractional crystallization from ethanol. All trans vitamin A acid has a melting point of 180° to 182°C and 9,10-cis vitamin A acid, which crystallized in the form of pale yellow fine needles collected into clusters, has a melting point of 189° to 190°C.

brand name

A-acido;Acid a vit;Acnavit;Acnavyse;Acretin;Airoderm;Aknebon;Aknefug;Anition;Antibio-aberel;Apsor;A-vitamisyre;Avitoin;Cordes vas;Dermoclar;Dermojuventas;Derugin;Locacid;Pigmanorm;R0 22-6595;Reiderma;Retin a;Ro 1-5488;Sebo-psor;Stie vaa;Stievaa;Tretin m;Vas dexa;Verra-med;Vitacid a.

Therapeutic Function

Keratolytic

World Health Organization (WHO)

Tretinoin, a retinol derivative, was introduced in 1973 exclusively for the topical treatment of severe acne. Preparations of tretinoin are indicated for topical use only since oral administration has been associated with risk of toxicity from hypervitaminosis-A and subsequently of teratogenicity.

General Description

Yellow to light-orange crystalline powder.

General Description

Tretinoin is available in 10-mg capsules for oral administrationin the treatment of APL. The mechanism of action involvespassive diffusion through the cell membrane andthen movement to the nucleus where it interacts with theretinoic acid receptor (RAR) portion of the PML-RAR fusionprotein. Binding of tretinoin allows the cell to differentiateand has also been shown to result in the destruction ofthe PML-RAR fusion protein. Resistance to tretinoin isproblematic and associated with an increase in cellularretinoic acid–binding proteins (CRAPBs) located in the cytosol.The complexation with tretinoin prevents movementinto the nucleus and may present the drug to metabolizingenzymes that inactivate it. Amino acid mutation of thePML-RAR protein has also been established as a mechanismof resistance. The agent is well absorbed upon oral administrationand highly (95%) protein bound. Metabolismoccurs in the liver and several inactive metabolites havebeen identified including 13-cis-retinoic acid, 4-oxo cisretinoic,4-oxo trans-retinoic acid and 4-oxo trans-retinoicacid glucuronide. Elimination occurs in the urine (63%) andfeces (31%) with an elimination half-life of 40 to 120 minutes.Vitamin A toxicity is seen in nearly all patients andpresents as headache, fever, dryness of the skin, skin rash,mucositis, and peripheral edema. APL differentiation syndromesuch as that seen for arsenic trioxide also occurs.Cardiovascular effects include flushing, hypotension, CHF,stroke, and myocardial infarction have been reported butoccur only rarely. There are also several CNS and GI effectsthat have been associated with the agent as well.

Air & Water Reactions

Tretinoin may be sensitive to prolonged exposure to air. Insoluble in water.

Reactivity Profile

Tretinoin may discolor on exposure to light. Tretinoin is extremely sensitive to exposure to light and, therefore, Tretinoin should be fully protected from light during all handling. Solutions are unstable in the presence of strong oxidizers. Tretinoin is incompatible with strong oxidizing agents. .

Fire Hazard

Flash point data for Tretinoin are not available; however, Tretinoin is probably combustible.

Biological Activity

Endogenous agonist for retinoic acid receptors. Also positively modulates PPAR δ receptors (K d = 17 nM). Promotes differentiation of embryonic stem cells (ESCs) into adipocytes, neurons and glia in vitro .

Biochem/physiol Actions

all?trans?Retinoic acid (ATRA) is a ligand for both the retinoic acid receptor (RAR) and the retinoid X receptor (RXR). The bound RAR and RXR act as transcription factors that regulate the growth and differentiation of both normal and malignant cells. Cytochromes P450 (CYPs) catalyze the 4-hydroxylation of ATRA. Retinoic acid primes embryonic stem cells to become neurons.

Clinical Use

The major toxic effect of tretinoin is erythema and irritation of the skin to which it is applied, especially if the skin is moist.This toxicity often decreases with continued therapy.

Toxicology

Oral retinoic acid has strong teratogenic effects on experimental animals (including mice, rats, hamsters, rabbits, monkeys, etc.) and humans[2]. Topical application of retinoic acid on the skin has clear embryotoxicity and teratogenicity to the mothers of mice, rats, hamsters and rabbits in the embryo sensitive period, and can cause maternal systemic toxicity. However, retrospective data so far have not found teratogenicity after topical administration of human skin. Retinoids are irritating to the skin. The skin reaction of the above-mentioned experimental animals is significantly heavier than the human reaction, which can cause different degrees of skin irritation, inflammation, redness, erosion, weakening of the stratum corneum barrier, increased drug absorption, and systemic toxicity depending on the drug concentration and the number of times of administration. Although external use on human skin is irritating, it does not have the above-mentioned serious reactions. It may be due to differences in skin structure and sensitivity to retinoic acid stimulation between animals and humans. Therefore, the safety data of local administration of retinoic acid in animals and its predictive significance for clinical drug safety should be carefully evaluated.

Safety Profile

Poison by ingestion, intraperitoneal, subcutaneous, and intravenous routes. Experimental reproductive effects. Questionable carcinogen with experimental neoplastigenic and teratogenic data. Human mutation data reported. A human skin irritant. When heated to decomposition it emits acrid smoke and irritating fumes. Used to treat acne and other skin problems.

Veterinary Drugs and Treatments

Topical tretinoin may be useful in treating localized follicular or hyperkeratotic disorders such as acanthosis nigrans, idiopathic nasal and footpad hyperkeratosis, callous pyodermas, or chin acne. Tretinoin’s exact mechanism of action is not well understood, but it stimulates cellular mitotic activity, increases cell turnover, and decreases the cohesiveness of follicular epithelial cells.

Drug interactions

Potentially hazardous interactions with other drugs
Antibacterials: possibly increased risk of benign intracranial hypertension with tetracyclines - avoid.
Antifungals: possible increased risk of tretinoin toxicity with fluconazole, ketoconazole and voriconazole.
Vitamin A: risk of hypervitaminosis - avoid.

Metabolism

Metabolised in the liver by the cytochrome P450 isoenzyme system to form isotretinoin, 4-oxo-transretinoic acid, and 4-oxo-cis-retinoic acid.
Tretinoin is excreted in the bile and the urine.

storage

Store at -20°C

Purification Methods

Purify the acid by chromatography on silicic acid columns, and eluting it with a small amount of EtOH in hexane. Also dissolve it in Et2O, wash it with H2O, dry (Na2SO4), evaporate and the solid residue is recrystallised from MeOH (0.53g /3.5mL MeOH to give 0.14g) or EtOH. It also recrystallises from i-PrOH, or as the methyl ester from MeOH. UV in MeOH has max at 351nm ( 45,000). 9-Cis-acid forms yellow needles from EtOH, with m 189-190o, and its UV in MeOH has max at 343nm ( 36,500); the 13-cis-acid forms red-orange plates from i-PrOH with m 174-175o, and UV has max at 345nm ( 39,800). Store it in the dark, in an inert atmosphere, at 0o [Robeson et al. J Am Chem Soc 77 4111 1955]. [Beilstein 9 IV 2387.]

References

1) Allenby (1993), Retinoic acid receptors and retinoid X receptors: interactions with endogenous retinoic acid; Proc. Natl. Acad. Sci. USA, 90 30 2) Dani et . (1997) Differentiation of embryonic stem cells into adipocytes in vitro; J. Cell Sci. 110 1279 3) Hu (2009) Differentiation Of Spinal Motor Neurons From Pluripotent Human Stem Cells; Nat. Protoc., 4 1295 4) Sasai (2002) Generation of dopaminergic neurons from embryonic stem cells J. Neurol., 249 II 41