WO 95/32741 А, 07.12.1995. Y.S.Lee et al. «Chiral synthesis of trans-1-Aminoindolo[2,3-]quinolizidine and trans-l-Aminobenzol[]quinolizidine Derivatives from L-Pyroglutamic Acid», The Journal of Organic Chemistry 1999, 64 (26), p.9727-9730. C.M.Acevedo et al. Synthesis and analysis of the sterically constrained L-glutamineanalogues (3S,4R)-3,4-dimethyl-L-glutamine and (3S,4R)-3,4-dimethyl-L-pyroglutamic acid, TETRAHEDRON 2001, 57, p.6353-6359. EP 0279307 A, 24.08.1988. RU 2059642 C1, 10.05.1996. WO 95/19186 A, 20.07.1995.