Add time:08/01/2019         Source:sciencedirect.com

α-Guanidinoglutaric acid (α-GGA) has been reported to occur in the cerebral cortex after epileptic seizures. No physical characteristics of α-GGA have been given. A practical procedure for the preparation of α-GGA is reported here. α-GGA forms a lactam in aqueous solution at 80°C. It is proposed to substitute this lactam, 1-amidino-2-pyrrolidone-5-carboxylic acid (pAGlu), for pyroglutamic acid (pGlu) at the N-terminal position in neuropeptides to modify their biological characteristics. l(+)-Glutamic acid was reacted with S-methylisothiourea (I) at pH 10 in aqueous solution to form l(−)-α-guanidinoglutaric acid: mp 165–168°C, [α]d22 = −22.7 (C = 4.2 m HCl). α-GGA reacted promptly with excess reagent to form a salt, S-methylisothiourea-α-guanidinoglutarate: mp 209–210°C, [α]d22 = −13.0 (C = 4,2 m HCl). I was removed from the salt with aqueous picric acid, since I readily formed an insoluble picrate, S-methylisothiourea picrate (mp 225–228°C). Alternatively, the salt was added to a cation exchange column, and the α-GGA was eluted with molar ammonium acetate buffer, pH 9.5. Its lactam, 1-amidino-2-pyrrolidone-5-carboxylic acid, mp 248–249°C, [α]d22 = +2.1 (C = 4,2 m HCl), formed a picrate (mp 196–199°C).

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