TABLE 4. Metabolites of S-1 identified in rat feces of 0 to 24 h (using mobile phase system 2).

Numbers in bold are values of m/z for basic mass peaks in the corresponding MS spectrum.

Metabolite Identification	Retention Time	[M - H]−	MS/MS	Sites of Biotransformation or Confirmed Structure
	min	m/z	m/z
1*	26.62	213	111	3-(4-Fluorophenoxy)-2-hydroxy-2-methyl-propanoic acid
9	29.40	467	387, 127; MS3 of 387→259, 201, 175 127; MS4 of 259→229, 209, 201, 175	Nitro reduction, mono-hydroxylation on the B-ring and sulfation
17	32.34	387	259, 127; MS3 of 259→201, 175	Nitro reduction and mono-hydroxylation on the B-ring
12	32.55	467	387, 127; MS3 of 387→259, 201, 175 127; MS4 of 259→230, 201, 175	Nitro reduction, mono-hydroxylation on the B-ring and sulfation
6	38	301	221; MS3 of 221→191, 171	Mono-hydroxylation on 4-nitro-3-trifluoromethyl-phenylamine and sulfation
38	38.14	467	387, 127; MS3 of 387→259, 201, 175 127; MS4 of 259→229, 209, 201, 175	Nitro reduction, mono-hydroxylation on the B-ring and sulfation
21	39.01	387	259, 201,127; MS3 of 259→229, 201, 175	Nitro reduction and mono-hydroxylation on the B-ring
39	40.18	451	371; MS3 of 371→259, 231, 201, 175, 111; MS4 of 259→201, 175	Nitro reduction and sulfation
29	44.84	387	259, 127	Nitro reduction and mono-hydroxylation on the B-ring
31	45.52	387	275, 255, 111; MS3 of 275→255	Nitro reduction and mono-hydroxylation on the A-ring or phenylamine on the A-ring
32	47.19	371	259, 231, 201, 175, 111; MS3 of 259→229, 201, 175	Nitro reduction
24	50.01	577	401, 307, 261, 205, 175	Glucuronidation of S-1
40	52.56	307	289, 245, 205; MS3 of 289→245, 204	O-Dephenylation (the B-ring) {2,3-dihydroxy-2-methyl-N-[4-nitro-3-(trifluoromethyl)-phenyl]-propanamide}

^*indicates that the structure of the metabolite has been confirmed using a synthetic standard in LC-MSⁿ.