Journal of Organometallic Chemistry 571 (1998) 21 – 29 X-ray crystallographic study of boroxazolidones obtained from L-ornithine, L-methionine, kainic acid and 2,6-pyridinedicarboxylic acid Jose ´ Trujillo a , Herbert Ho ¨pfl b , Dolores Castillo c , Rosa Santillan c , Norberto Farfa ´n c, * a Seccio ´n de Graduados y Departamento de Bioquı ´mica, Escuela Superior de Medicina, Instituto Polite ´cnico Nacional, Apartado Postal 42 -161, CP 11340 Me ´xico DF, Me ´xico b Uniersidad Auto ´noma del Estado de Morelos, Centro de Inestigaciones Quı ´micas, A. Uniersidad 1001, CP 62210 Cuernaaa, Morelos, Me ´xico c Departamento de Quı ´mica, Centro de Inestigacio ´n y de Estudios Aanzados del IPN, Apartado Postal 14 -740, CP 07000 Me ´xico DF, Me ´xico Received 3 April 1998; received in revised form 20 July 1998 Abstract In the present contribution, the boroxazolidones prepared from L-ornithine, L-methionine, kainic acid and 2,6-pyridinedicar- boxylic acid have been studied by X-ray crystallography. A comparison of the structural data with corresponding boroxazolidi- nes, bicyclic boronates and tricyclic borates has shown that in boron complexes with a boroxazolidone ring the B–O bond is longer in comparison to boron complexes with a boroxazolidine ring. At the same time the N B bond length is shorter indicating that the hydrolytic stability of the complexes with boroxazolidone rings is enhanced. © 1998 Elsevier Science S.A. All rights reserved. Keywords:  -Amino acids; Kainic acid; Boron complexes; Boroxazolidones; Boroxazolidines; Hydrolytic stability 1. Introduction For the past few years we have been interested in the synthesis and characterization of five- and six- membered borinates with a coordinative N B bond [1 – 6], one important class being the five-membered boroxazolidones [7]. Such boroxazolidones are readily prepared by condensation of  -amino acids and di- alkyl- or diarylborinic acids [7,8]: In these complexes with a coordinative N B bond both functional groups of the  -amino acid are simul- taneously bound to the boron atom. The hydrolytic stability is maintained in aqueous solution at pH 2–7 and the boroxazolidone ring does not decompose even in boiling water [9–12]. The simultaneous protection of the amino and car- boxyl group in  -amino acids renders boroxazolidones into useful reagents for selective reactions on further functional groups in the side chain of the correspond- ing  -amino acids [12,13]. Furthermore, studies with [N,N -dimethylglycinato-O,N ]borane have shown that the methylene hydrogen atoms between the coordi- nated amino and carboxyl groups are sufficiently acidic to undergo deprotonation and subsequent reac- tion with an electrophilic substrate [9], opening up the possibility of synthesizing substituted  -amino acids from N,N - dimethylglycine. The hydrolysis of boroxa- * Corresponding author. Tel.: +52 5 7577113; fax: +52 5 7577000; e-mail: jfarfan@mail.red.cinvestav.mx 0022-328X/98/$ - see front matter © 1998 Elsevier Science S.A. All rights reserved. PII S0022-328X(98)00893-6