Some trimethylsilyl derivatives of nicotianamine and related amino acids have been studied by capillary gas chromatography/mass spectrometry. This method gives useful data for structure determination.
INTRODUCTIONNicotianamine (1) has been identified as the 'normalizing factor' which restores growth, development and chlorophyll synthesis of the nicotianamine-less mutant chloronerua of Lycopersicon esculentum Mill.' This amino acid proved to be of general distribution in the plant A series of analogues were synthesized, e.g. 5," 13,5 16,5 216 and 24,6 to study their biological activities.' The hitherto known phytosiderophores possess related structures, e.g. mugineic acid (9)' or avenic acid A (19).' Mass spectrometry was used in the structure determination of these compounds. Field desorption only gives quasi-molecular ions," whereas electron impact (EI) is not very suitable for these polar amino acids.' Therefore, some derivatives were studied,"." but a systematic investigation in this field is not available. The present paper deals with capillary gas chromatography/mass spectrometry (GC/MS) measurements on trimethylsilyl (TMS) derivatives.
EXPERIMENTAL GCWSA Varian 3700 gas chromatograph combined with a Finnigan MAT 312 mass spectrometer was used. GC was performed on a 30 m x 0.32 mm id. methylpolysiloxane fused-silica column, film thickness 0.20 pm, with hydrogen as a carrier gas (2 ml min-I). Temperatures: injection, 280 "C, ion source, 200 "C; temperature programme: from 80 "C (2 min) to 280 "C (3 "C min-', 30 min). The EI energy was 70 eV.
Linear retention indices (LRI)A mixture of standard hydrocarbons with even numbers of carbon atoms (Clo to c28) was used.
High-resolution mass spectrometryA Finnigan MAT 8500 was used (resolution 10000). The EI energy was 70 eV.
Preparation of TMS derivativesAmino acid (0.26-1.0 mg) was heated with 50 p1 of 2,2, 2-trifluoro-N-methyl-N-TMS-acetamide in a small reaction vial equipped with screw cap and teflon/silicone septum at 50 "C for 24 h. The N-TMS amino acid esters are stable for a period of at least six days when stored at 5 "C in a tightly capped vial. Reaction at 100 "C for 3 h gives lower yields and other ratios of the TMS derivatives.
RESULTS AND DISCUSSIONAfter trimethylsilylation of nicotianamine (1) and the analogous amino acids 5,9,13,16,19,21 and 24 several derivatives are observed in general which differ in the number of TMS groups and in the formation of lactam rings' (see formulae 1-26). Only y-lactams are produced. Lactam formation could occur thermally in the gas chr~matograph,'~ e.g. formation of 4 from 2. Only one hydrogen of the primary amino groups is replaced by TMS. Table 1 displays the LRI. The important ions in the mass spectra are listed in Table 2. The structures of 'further ions' of Table 2