X6???X5???X4???NH2 [0370] (e) reacting said amino group with a folate moiety; and [0371] (f) cleaving the protecting groups on said hydroxyl groups of step (b) to form a compound of formula XVII. [0372] The methods of the present invention also provide compounds of the formula XVII wherein R4 is a hydroxyl group protected with C1-C10 alkyl, C2-C10 alkenyl or C2-C20 alkynyl, the methods further com