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Rosental area, WRO-1047-3
Mattenstrasse 24
4058 Basel, Switzerland

Tel: + 41 61 685 95 00
E-mail: contact@spirochem.com


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The pentafluorosulfanyl group (SF5) has been known since the 1950’s, but until recently, it was mostly considered as a chemical oddity, mainly studied for its electronic properties in material science. The SF5 group is indeed very strongly electronegative and, when placed on aromatic rings, is the second most electron-withdrawing group after the nitro group, leading to a lot of research in the field of polymers, liquid crystals and other material. Beyond the electronic properties, which can be used to modulate the pKa of nitrogens around the aromatic ring, the SF5 group has very interesting properties. It is a very stable moiety, resistant to hydrolysis and oxidation. It is also very lipophilic, although less than one would think. It is actually less lipophilic than the more common tert-butyl group and slightly more lipophilic than the CF3 group. In terms of volume, the SF5 group is smaller than the tert-butyl group and slightly bigger than the CF3 group.

Despite all these interesting properties, SF5 fragments have not yet been used extensively in drug discovery. The main reason for this is probably the lack of diversity of commercially available building blocks containing SF5. Indeed, until recently, only simple SF5 building blocks (phenyl-SF5, tolyl-SF5 etc.) were available and discovery chemists had to perform several chemical transformations to make useful building blocks.

SpiroChem is a leading company in the field of bioisosteres and we identify the SF5 as potential replacements for lipophilic groups in our LipoSwitch concept. In order to make the SF5 groups readily incorporated in medicinal chemistry projects, we had to expand the scope of SF5 building blocks with medchem-relevant examples. For example, SpiroChem pioneered the commercialization of benzofused heteroarenes. Since our first move in the field, the SF5 has been studied in medicinal chemistry context by academic groups and more data is now available, showing the beneficial effect of SF5 over tert-butyl groups to improve ADME properties.1


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