Linezolid Hydroxymethyl Impurity

8-[(3R)-3-Amino-1-piperidinyl]-1-[[4-[[2-[[8-[(3R)-3-amino-1-piperidinyl]-7-(2-butyn-1-yl)-2, 3, 6, 7-tetrahydro-3-methyl-2, 6-dioxo-1H-purin-1-yl]methyl]-1, 4-dihydro-4-ethyl-4-quinazolinyl]methyl]-2-quinazolinyl]methyl]-7-(2-butyn-1-yl)-3, 7-dihydro-3-methyl-1H-purine-2, 6-dione ;