Releasable linkage and compositions containing same

DETAILED DESCRIPTION Accordingly, it is an object of the invention to provide a compound where a ligand is covalently yet reversibly linked to a hydrophilic polymer.
Upon cleavage of the linkage, the ligand in its native form is regenerated.
In one aspect, the invention includes a compound having the general structure: ##STR1## wherein R.
sup.
1 is a hydrophilic polymer comprising a linkage for attachment to the dithiobenzyl moiety; R.
sup.
2 is selected from the group consisting of H, alkyl and aryl; R.
sup.
3 is selected from the group consisting of O(C.
dbd.
O)R.
sup.
4, S(C.
dbd.
O)R.
sup.
4, and O(C.
dbd.
S)R.
sup.
4 ; R.
sup.
4 comprises an amine-containing ligand; and R.
sup.
5 is selected from the group consisting of H, alkyl and aryl; and where orientation of CH.
sub.
2 --R.
sup.
3 is selected from the ortho position and the para position.
In one embodiment, R.
sup.
5 is H and R.
sup.
2 is selected from the group consisting of CH.
sub.
3, C.
sub.
2 H.
sub.
5 and C.
sub.
3 H.
sub.
8.
In another embodiment, R.
sup.
2 and R.
sup.
5 are alkyls.
In another embodiment, the amine-containing ligand R.
sup.
4 is selected from the group consisting of a polypeptide, an armine-containing drug and an amine-containing lipid.
In an embodiment where the amine-containing ligand R.
sup.
4 is an amine-containing lipid, the lipid includes either a single hydrocarbon tail or a double hydrocarbon tail.
In one preferred embodiment, the lipid is a phospholipid having a double hydrocarbon tail.
The hydrophilic polymer R.
sup.
1 can be, in yet another embodiment, selected from the group consisting of polyvinylpyrrolidone, polyvinylmethylether, polymethyloxazoline, polyethyloxazoline, polyhydroxypropyloxazoline, polyhydroxypropyl-methacrylamide, polymethacrylamide, polydimethyl-acrylamide, polyhydroxypropylmethacrylate, polyhydroxyethylacrylate, hydroxymethylcellulose, hydroxyethylcellulose, polyethyleneglycol, polyaspartamide, copolymers thereof, and polyethyleneoxide-polypropylene oxide.
In one preferred embodiment, the hydrophilic polymer R.
sup.
1 is polyethyleneglycol