*3.4. Synthesis of Regioisomers 13 and 14*

A solution of 1*H*-indole-4,7-dione (**10**, 504 mg, 3.4 mmol) in MeCN (160 mL) was treated with a solution of 2-aminoethanesulfinic acid (482 mg, 4.42 mmol) in H2O (50 mL) in one portion and the mixture stirred for 20 h under an atmosphere of O2. The MeCN and H2O were removed by rotary evaporation to afford an orange solid, which was purified by flash chromatography (silica, 1:5 *v*/*v* MeOH/CH2Cl2 elution) to afford a 3.3:1 mixture of regioisomers **14** and **13**, respectively (307 mg, 36%). A portion of this material (40 mg) was pre-adsorbed to C18-bonded silica (1 g) overnight, then packed into a guard cartridge that was attached to a C18-bonded silica semi-preparative HPLC column. Isocratic HPLC conditions of 95% H2O (0.1% TFA)/5% MeOH (0.1% TFA) were employed for the first 10 min, then a linear gradient to 50% H2O (0.1% TFA)/50% MeOH (0.1% TFA) was run over 40 min, followed by a linear gradient to MeOH (0.1% TFA) in 1 min, then isocratic conditions of MeOH (0.1% TFA) for a further 9 min, all at a flow rate of 9 mL/min. Sixty fractions (60 × 1 min) were collected by time from the start of the HPLC run. All UV active fractions were analyzed by 1H-NMR spectroscopy and MS, and identical fractions were combined. This yielded **14** (5.0 mg, 1%, <sup>t</sup> R = 25.0–27.0 min) as a bright orange powder.

Compound **14**: Bright orange amorphous solid; 1H-NMR (500 MHz, DMSO-*d*6) δ<sup>H</sup> 3.28–3.33 (2H, m, H-2), 3.79–3.82 (2H, m, H-3), 6.53 (1H, d, *J* = 2.5 Hz, H-8), 7.40 (1H, d, *J* = 2.5 Hz, H-7), 8.89 (1H, br s, H-4), 12.81 (1H, br s, H-6); 13C-NMR (125 MHz, DMSO-*d*6) *δ*<sup>C</sup> 39.3 (C-3), 48.4 (C-2), 108.4 (2C, C-9a, C-8), 127.2 (C-8a), 128.2 (C-5a), 130.1 (C-7), 147.5 (C-4a), 167.9 (C-5), 174.7 (C-9); (+)-LRESIMS *m*/*z* (rel. int.) 253 (100) [M + H]+; (−)-LRESIMS *<sup>m</sup>*/*<sup>z</sup>* (rel. int.) 251 (100) [M − H]−; (+)-HRESIMS *<sup>m</sup>*/*<sup>z</sup>* 275.0087 [M + Na]<sup>+</sup> (calcd for C10H8N2NaO4S, 275.0097).

#### *3.5. Synthesis of Regioisomers 15 and 16*

A 3.3:1 regioisomeric mixture of **14** and **13** (90 mg, 0.36 mmol) from the synthesis described above (Section 3.4) in a solution of MeOH (10 mL) was treated with an aqueous KOH solution (6 mL, 12 M). The magnetically stirred reaction mixture was purged with O2, and maintained at 60 ◦C under a balloon of O2 for 4 h. The reaction mixture was cooled to 0 ◦C, carefully neutralized by the addition of an aqueous solution of HCl (1 M) and then the mixture was concentrated *in vacuo* to afford a residue that was subjected to flash chromatography through a small plug of silica (1:10 *v*/*v* MeOH/CH2Cl2 elution) and after concentration of the eluent *in vacuo*, the residue (40 mg) was pre-adsorbed to C18-bonded silica (1 g) overnight, then packed into a guard cartridge that was attached to a C18-bonded silica semi-preparative HPLC column. Application of same reversed-phase HPLC purification method described above (Section 3.4) resulted in the purification of compounds **16** (15 mg, 17%, <sup>t</sup> R = 28.0–30.0 min) and **15** (5 mg, 6%, <sup>t</sup> R = 32.0–34.0 min) as yellow and orange powders, respectively.

Compound **15**: Orange amorphous solid; 1H-NMR (500 MHz, DMSO-*d*6) δ<sup>H</sup> 6.49 (1H, d, *J* = 8.8 Hz, H-2), 6.66 (1H, d, *J* = 2.8 Hz, H-6), 7.07 (1H, d, *J* = 8.8 Hz, H-3), 7.27 (1H, d, *J* = 2.8 Hz, H-7), 11.07 (1H, br s, H-4), 12.99 (1H, br s, H-8); 13C-NMR (125 MHz, DMSO-*d*6) δ<sup>C</sup> 108.0 (C-6), 111.7 (C-2), 113.4 (C-9a), 121.8 (C-5a), 126.8 (C-7), 130.2 (C-3), 131.3 (C-8a), 140.5 (C-4a), 172.2 (C-9), 174.1 (C-5); (+)-LRESIMS *<sup>m</sup>*/*<sup>z</sup>* (rel. int.) 251 (100) [M + H]+; (−)-LRESIMS *<sup>m</sup>*/*<sup>z</sup>* (rel. int.) 249 (100) [M − H]−; (+)-HRESIMS *m*/*z* 272.9939 [M + Na]<sup>+</sup> (calcd for C10H6N2NaO4S, 272.9940).

Compound **16**: Yellow amorphous solid; 1H NMR (500 MHz, DMSO-*d*6) δ<sup>H</sup> 6.42 (1H, d, *J* = 8.8 Hz, H-2), 6.60 (1H, d, *J* = 2.6 Hz, H-8), 7.04 (1H, d, *J* = 8.8 Hz, H-3), 7.43 (1H, d, *J* = 2.6 Hz, H-7), H-4 and H-6 not observed; 13C-NMR (125 MHz, DMSO-*d*6) δ<sup>C</sup> 108.5 (C-8), 111.6 (C-2), 113.9 (C-9a), 126.9 (C-8a), 127.6 (C-5a), 129.8 (C-7), 130.1 (C-3), 140.2 (C-4a), 167.9 (C-5), 177.3 (C-9); (+)-LRESIMS *m*/*z* (rel. int.) 251 (100) [M + H]+; (−)-LRESIMS *<sup>m</sup>*/*<sup>z</sup>* (rel. int.) 249 (100) [M − H]−; (+)-HRESIMS *<sup>m</sup>*/*<sup>z</sup>* 272.9933 [M + Na]<sup>+</sup> (calcd for C10H6N2NaO4S, 272.9940).
