Chemical Properties
(+)-Abscisic acid (pure substance) is a colorless crystalline solid. It has a melting point of 160–161°C and sublimes at 120°C. The partition coefficients are 1.8 for the electrically neutral form and 0.94 for the ionic form. Its relative density is 1.21. The solubility in water is 3102 mg/L (at pH 4). The specific rotation is [α]²⁰D = +40.997° (c = 10.1 mg/mL in ethanol, at 20°C). The pKa is 4.61. It is soluble in chloroform, acetone, ethyl acetate, and diethyl ether but only sparingly soluble in benzene and water. The UV maximum absorption wavelength (in methanol) is 252 nm.
Uses
(+)-Abscisic acid is the natural isomer of the abscission-accelerating plant hormone and a plant growth regulator that exhibits multiple physiological effects, including inducing plant dormancy, inhibiting seed germination and plant growth, and stimulating stomatal closure.
Definition
ChEBI: The naturally occurring (1'S)-(+) enantiomer of abscisic acid. It is an important sesquiterpenoid plant hormone which acts as a regulator of plant responses to environmental stresses such as drought and cold.
Biochem/physiol Actions
Plant hormone and growth regulator that is involved in several physiological mechanisms including seed dormancy, leaf abscission, stomatal movement, and plant stress responses. Through complex interactions with several intracellular signaling systems, it can regulate the expression of hundreds of plant genes.
Synthesis
Enantioselective total synthesis of (+)-Abscisic acid (ABA)[1]:
Purification Methods
Crystallise the acid from CCl4/pet ether, EtOH/hexane and sublime it at 120o. Also purify it by dissolving ~30g in 30mL of EtOAc, adding 100mL of hexane and allow to crystallise overnight (yield 8.4g), m 156-158o, 161-163o, [] D +426o (c 0.005M H2SO4 in MeOH). [Cornforth et al. Nature (London) 206 715 1965, Soukemp et al. Helv Chim Acta 72 361 1989.] The RS-isomer was purified on a Kieselgel F254 plate with toluene/EtOAc/AcOH (50:50:3) and has m 188-190o [Cornforth et al. Aust J Chem 45 179 1992]. [Beilstein 17/3 V 13.]
References
[1] Concise and Practical Total Synthesis of (+)-Abscisic Acid. ACS Omega 2020, 5, 22, 13296–13302. DOI:
10.1021/acsomega.0c01332
