Abstract: The present invention provides a compound comprising a steroidal ring system and an optional group R1 selected from any one of —OH, a sulphamate group, a phosphonate group, a thiophosphonate group, a sulphonate group or a sulphonamide group; wherein the D ring of the steroidal ring system is substituted by a group R2 of the formula -L-R3, wherein L is an optional linker group and R3 is selected from groups which are or which comprise one of a nitrite group, an alcohol, an ester, an ether, an amine and an alkene, provided that when R3 is or comprises an alcohol, L is present; and wherein the A ring of the steroidal ring system is substituted at position 2 or 4 with a group R4, wherein R4 is a hydrocarbyl group.