title: The lactam of alpha-guanidinoglutaric acid (1-amidino-2-pyrrolidone-5-carboxylic acid).
abstract: alpha-Guanidinoglutaric acid (alpha-GGA) has been reported to occur in the cerebral cortex after epileptic seizures. No physical characteristics of alpha-GGA have been given. A practical procedure for the preparation of alpha-GGA is reported here. alpha-GGA forms a lactam in aqueous solution at 80 degrees 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(-)-alpha-guanidinoglutaric acid: mp 165-168 degrees C, [alpha]22D = -22.7 (C = 4, 2 M HCl). alpha-GGA reacted promptly with excess reagent to form a salt, S-methylisothiourea-alpha-guanidinoglutarate: mp 209-210 degrees C, [alpha]22D = -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 degrees C). Alternatively, the salt was added to a cation exchange column, and the alpha-GGA was eluted with molar ammonium acetate buffer, pH 9.5. Its lactam, 1-amidino-2-pyrrolidone-5-carboxylic acid, mp 248-249 degrees C, [alpha]22D = +2.1 (C = 4, 2 M HCl), formed a picrate (mp 196-199 degrees C).
mesh_terms: D055598:Chemical Phenomena; D002621:Chemistry; D005971:Glutamates; D018698:Glutamic Acid; D005977:Glutarates / Q000138:chemical synthesis; D007550:Isothiuronium / Q000031:analogs & derivatives; D009682:Magnetic Resonance Spectroscopy; D009904:Optical Rotation; D010851:Picrates; D011760:Pyrrolidinones / Q000138:chemical synthesis*; D013055:Spectrophotometry, Infrared
chemical_list: D005971:Glutamates; D005977:Glutarates; D010851:Picrates; D011760:Pyrrolidinones; C049785:1-amidino-2-pyrrolidone-5-carboxylic acid; D007550:Isothiuronium; D018698:Glutamic Acid; C028262:alpha-guanidinoglutaric acid; C005858:picric acid; C027744:S-methylisothiopseudouronium