This alkaloid is isolated as the oxalate from the leaf extract of Rauwolfia canescens L. from which the free base may be obtained as colourless needles which are laevorotatory with [α]30D - 40° (EtOH). The alkaloid forms crystalline salts: the hydrochloride, m.p. 27S-2S00C (dec.); [α]30D + 74° (H20); nitrate, m.p. 257-SoC (dec.); oxalate, m.p. 245-6°C and the picrate, m.p. 20SoC. Two active hydrogens are present and the alkaloid furnishes a monoacetyl derivative, m.p. 2l6-SoC (dec.). Treatment with concentrated ammonia solution at room temperature converts the base into rauwolscinic acid, C2oH2403N2.H20, m.p. 262-4°C (dec.); [α]23D + l36.So (H20) which yields a crystalline hydrochloride, m.p. 255.5-257.5°C (dec.) and on esterification with MeOH reverts to the original alkaloid. On distillation with Zn dust, rauwolscine yields harman, 2-methylindole (skatole) and isoquinoline.
Chakravarti has shown that the alkaloid is a cardiovascular depressant, shows hypotensive activity and is relatively highly toxic.
Standard alpha-2 adrenergic antagonist
Rauwolscine is a natural alkaloid that acts as a selective and reversible α2-adrenergic receptor antagonist (Ki = 12 nM). It is a stereoisomer of yohimbine, which potently antagonizes both α1- and α2-adrenergic receptors. Rauwolscine also acts as a receptor antagonist at the serotonin 5-HT2B receptor (Ki = 14.3 nM) and as a weak partial agonist at 5-HT1A (IC50 = 1.3 μM).The α2-adrenergic receptor has diverse physiological functions and antagonists like rauwolscine have numerous applications, including the modulation of mood and behavior.
Rauwolscine hydrochloride is a standard α2-adrenergic antagonist (Ki values are 3.5, 4.6, and 0.6 nM at cloned human α2A, α2B, and α2C-adrenoceptors respectively). Partial agonist at 5-HT1A receptors. Also available as part of the α2-Adrenoceptor Tocriset? .
Mukherjee., J. Ind. Chern. Soc., 18, 33, 485 (1941)
Mukherjee., ibid, 20, 11 (1943)
Mukherjee., ibid, 23, 6 (1946)
Pharmacology:
Chakravarti., Sci. Cult., (Calcutta), 7, 45S (1942)
