Synthetic routes to potent steroidal and nonsteroidal sulfamate-based active site-directed inhibitors of the enzyme steroid sulfatase, a topical target in the treatment of postmenopausal women with hormone-dependent breast cancer, are described. Novel compounds were examined for estrone sulfatase (E1-STS) inhibition in intact MCF-7 breast cancer cells and placental microsomes. Reaction of the sodium salt of estrone with sulfamoyl chloride gave estrone 3-O-sulfamate (EMATE, 2) which inhibits E1-STS activity potently (>99% at 0.1 mM in intact MCF-7 cells, IC50 = 65 pM) in a time- and concentration-dependent manner, suggesting that EMATE is an active site- directed inhibitor. EMATE is also active in vivo orally. 5,6,7,8- Tetrahydronaphthalene 2-O-sulfamate(7) and its N-methylated derivatives (8 and 9) were synthesized, and 7 inhibits the E1-STS activity in intact MCF-7 cells by 79% at 10 µM. 4-Methylcoumarin 7-O-sulfamate (COUMATE) and its derivatives (14, 16, and 18) wee prepared to extend this series of nonsteroidal inhibitors, and COUMATE educes the E1-STS activity in placental microsomes by >90% at 10 µM. Although the orally active COUMATE is less potent than EMATE as an active site-directed inhibitor, it has the important advantage of being nonestrogenic. Analogues (20, 22, 24, 26, 27, 31, 33, 39, and 44) of COUMATE were synthesized to study its structure-activity relationships, and sulfamates of tetralones (46 and 48) and indanones (49, 51, and 53) wee also prepared. While most of these compounds were found to inhibit E1-STS activity less effectively than COUMATE, one analogue, 3,4- dimethylcoumarin 3-O-sulfamate (24), was found to be some 12-fold more potent than COUMATE as an E1-STS inhibitor in intact MCF-7 cells (IC50 = 30 nM for 24, cf. 380 mM for COUMATE). Hence, highly potent sulfamate-based inhibitors of steroid sulfatase, such as EMATE, COUMATE, and 24, possess therapeutic potential and will allow the importance of estrogen formation in breast tumors via the E1-STS pathway to be assessed. A pharmacophore for active site-directed sulfatase inhibition is proposed.