. "Groups that have been found to be particularly useful for R5 include alkoxy-substituted alkyl groups such as --CH2 CH2 OCH3, CH2 CH2 OC2 H5, and --(CH2)3 OCH(CH3)2 ; alkanoic acids such as --(CH2)5 COOH; and multi-hydroxyl substituted alkyl groups such as the group derived from d-glucamine." . . .