β-Nitraminoalanine and its decarboxylation product N-nitroethylenediamine were identified in Agaricus silvaticus. A survey of secondary amino acids in mushrooms [1] revealed the presence of two new amino acids in Agaricus silvaticus Vitt. ex Fr. from North Carolina and in a closely related Puget Sound species [2] sometimes referred to as A. silvaticus. Electrophoresis at pH 2 and 6 suggests that one of the new compounds is as acidic as aspartic acid and the other is basic. Both give the same transiently-abnormal ninhydrin reaction: initial bright yellow, turning brown and, finally, brownish purple in a few hr. The electrophoretic behavior, chromatographic mobility and identity of ninhydrin reactions suggests that the basic compound is the decarboxylation product of the acidic amino acid. The acidic amino acid was isolated by cationic and anionic exchange enrichment, followed by chromatography and crystallization. The elemental analysis showed an unusually high nitrogen content: C₃H₇N₃O₄. The PMR in D₂O consisted of a two-proton doublet and a one-proton triplet typical of a β-substituted alanine. The remaining four hydrogens are exchangeable. Chemical ionization MS confirmed the molecular formula C₃H₇N₃O₄ (M + 1 = 150). The most distinctive feature of the MS was the dominant β-cleavage (m/e = 88, base peak) confirmed as a direct decomposition product of the quasimolecular ion at m/e 150 by observation of the metastable at m/e 51.7. The complementary β-cleavage ion (with H transfer) was also observed at m/e 60 as well as minor fragments due to loss of CO₂ (m/e 106) and H₂O (m/e 132). The elemental analysis, PMR and MS require an alanine having a β-substituent of composition HN₂O₂. Although quite a few isomeric HN₂O₂ groups are possible, only two, N-nitroamine and N-nitrosohydroxylamine, appear to have any stability. Therefore, the new amino acid would be either 1 or 2. The two can be conveniently distinguished by UV [3]. The λₘₐₓ of simple aliphatic N-nitroamines, ca 230 nm (ε 7000), is virtually unchanged by shifting pH from 1 to 13, while the maximum for N-nitrosohydroxylamines shifts from 230 nm (ε 6000) in acid or water to about 250 nm (ε 8000) in dilute NaOH. The UV spectrum of the new amino acid, λₘₐₓ 230 nm (ε 7700) remains the same at pH 1, 6 and 13. The new amino acid is therefore 1. Its isomer 2, alanosine, has been discovered previously in a Streptomycetes [4]. The isomeric naturally-occurring amino acids 1 and 2 are readily distinguished by PMR as well as by UV. In aqueous NaOD the α-proton triplet of alanosine occurs upfield of the β-methylene doublet, while in the PMR of β-nitraminoalanine in aq Na₂CO₃ the relative positions of these signals is just reversed. The logical structure 3 for the other new compound was proved by synthesis of N-nitroethylenediamine from ethylenediamine. The mp, IR, UV and PMR of the natural and synthetic compound were identical. One other related compound, N-nitroglycine, has been found as a natural product in Streptomyces noursei [5].