**4. Synthesis of SHetA2**

**GI50 Mean Graph for SHetA2 (NSC 726189) [33]**

72 Anti-cancer Drugs - Nature, Synthesis and Cell

Cancer panel Cell line Log GI50 (SHetA2) Log GI50 (ATRA)

HL-60(TB) −4.5 −4.7 K-562 −5.0 −4.3 MOLT-4 −4.7 −4.3 RPMI-8226 −4.5 −5.7 SR −4.9 −4.2

EKVX −4.9 −4.0 HOP-62 −4.7 −4.2 HOP-92 −4.7 −4.0 NCI-H226 −4.9 −4.3 NCI-H23 −4.9 −4.2 NCI-H322M −5.0 −4.0 NCI-H460 −4.6 −4.2 NCI-H522 −5.0 −4.2

HCC-2998 −5.4 −4.2 HCT-116 −4.8 −4.2 HCT-15 −4.9 −4.2 HT29 −4.6 −4.2 KM12 −5.0 −4.3 SW-620 −4.8 −4.2

SF-295 −5.0 −4.2 SF-539 −5.0 −4.2 SNB-19 −4.7 −4.2 SNB-75 −4.8 −4.0 U251 −5.0 −4.2

MALME-3M −5.6 −4.3 M14 −4.7 −4.2 MDA-MB-435 −4.9 −4.2 SK-MEL-2 −5.0 −4.4 SK-MEL-28 −4.8 −4.2 SK-MEL-5 −5.0 −4.2 UACC-257 −4.9 −4.2 UACC-62 −5.0 −4.0

Leukemia CCRF-CEM −4.9 −4.2

Nonsmall-cell lung carcinoma A549/ATCC −4.9 −4.3

Colon cancer COLO 205 −4.9 −4.2

CNS (gliomas) SF-268 −4.6 −4.0

Melanoma LOX IMVI −4.9 −4.4

Ovarian cancer IGROV1 −5.0 −4.0

The synthesis of SHetA2 mainly involved the preparation of the intermediate, aminothiochroman (**Figures 3** and **4**). Early synthetic procedure (**Figure 3**) involved using Fe/HOAc to reduce the nitro group with a yield of 40% [6]. The nitration reaction was the problematic step with only a 26% yield, since many additional by-products were formed in this reaction. In order to address this issue, Tallent et al. employed a nitrogen-containing starting material (4-acetamidobenzenethiol) [37] (**Figure 4**). They used methyllithium instead of methylmagnesium bromide to form the intermediate carbinol. In the cyclization procedure to form the thiochroman, chlorobenzene was used as solvent with a 58% yield avoiding the use of flammable and noxious CS2. This method circumvented the low-yielding nitration step and the subsequent reduction step to generate the amine group of aminothiochroman. The improved synthesis was shorter and afforded a 5-fold higher overall yield. The final product, SHetA2, was formed by reacting the aminothiochroman with 4-nitrophenyl isothiocyanate in tetrahydrofuran (**Figure 4**).

**Figure 3.** Synthesis of aminothiochroman.

**Figure 4.** Improved synthesis of aminothiochroman and SHetA2.
