s, or together with R2 or R4 is a lower alkylene bridge of 2-4 carbon atoms; R4 is hydrogen, a lower alkyl group of 1-6 carbon atoms or together with R3 is a lower alkylene bridge of 2-4 carbon atoms; or an amino group; R5 is hydrogen, or a lower alkyl group of 1-6 carbon atoms; with the proviso that at least one of R1, R2, R3, R4 or R5 is other than hydrogen; or R is an acyl or a lower alkylsulfo