The synthesis and characterization of polypeptide-adriamycin conjugates and its complexes with adriamycin. Part I

Poly(α-l-glutamic acid) (PGA) was grafted with amino acid and oligopeptide spacers up to 5 amino acids with the use of N,N'-carbonyldiimidazole and 2,3-dihydro-1,2-benz-isothiazole-3-on-1, 1-dioxide (saccharin) as an additive, and these polypeptides were characterized. The antitumor antibiotic adriamycin was covalently coupled via an amide bond onto PGA and onto the grafted polymers with the use of N-ethoxycarbonyl-2-ethoxy-1, 2-dihydroquinoline (EEDQ); these conjugates were characterized. The conjugates containing Gly—Gly—l-Leu spacer arms did yield free adriamycin upon digestion with papain. Adriamycin gave fairly stable complexes with PGA—adriamycin and branched poly peptide—adriamycin conjugates; these complexes were characterized

Optimization of macromolecular prodrugs of the antitumor antibiotic adriamycin

In our earlier work [10] on aminoribosyl-bound prodrugs of adriamycin (ADR) using poly(α-l-glutamic acid) (PGA) grafted in high yield (90–100 mol.%) with various peptide spacers as a plasma-soluble macromolecular carrier we observed rather low cytotoxic activities in L1210 leukemia and B16 melanoma in vitro assays. These results may be tentatively explained by a decreased susceptibility of the spacer-bound adriamycin moiety to hydrolysis by lysosomal enzymes due to the high spacer load. This hypothesis was tested by the study of two conjugates prepared by a different route. Peptide conjugates of adriamycin (Gly-Gly-Leu—ADR and Gly-Gly-Gly-Leu—ADR) were synthesized using the trityl N-protecting group and were coupled to PGA in 4.5 mol.% load according to the method described earlier [11]. However, these conjugates were almost totally devoid of cell growth-inhibiting activity in L1210 and B16 in vitro tests. The data suggest that either the uptake of the polymeric prodrugs into the cell by pinocytosis is highly dependent on spacer load or molecular weight, or that lysosomal digestion is too slow for efficient release of ADR. Possibly, enzymatic degradation of PGA which is known to occur only between pH 4 and 6 is rate-limiting for release of the drug. Current studies include the enzymatic degradation of PGA—peptide spacer—drug systems using p-nitroaniline as a model drug and papain as the enzyme. By variation of the length and load of spacer it can be estimated under which conditions the release of drug (using UV spectrometry) is faster than degradation of the polymer (as determined by viscometry). In addition, the uptake of PGA and derivatives with a fluorescent label into tumor cells is studied using laser flow cytometry and laser microscopy

Synthesis of 5-O-α- and -β-D-glucopyranosyl-D-glucofuranose and 5-O-α-D-glucopyranosyl-D-fructopyranose (leucrose)

Reaction of 1,2-O-cyclopentylidene-α-D-glucofuranurono-6,3-lactone (2) with 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide (1) gave 1,2-O-cyclopentylidene- 5-O-(2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl)-α-D-glucofuranurono-6,3-lactone (3, 45%) and 1,2-O-cyclopentylidene-5-O-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)-α-D-glucofuranurono-6,3-lactone (4, 38%). Reduction of 3 and 4 with lithium aluminium hydride, followed by removal of the cyclopentylidene group, afforded 5-O-α-(9) and -β-D-glucopyranosyl-D-glucofuranose (12), respectively. Base-catalysed isomerization of 9 yielded crystalline 5-O-α-D-glucopyranosyl-D-fructopyranose (leucrose, 53%)

Synthesis of 5-O-β-D-galactofuranosyl-D-galactofuranose

Conversion of benzyl alpha beta-D-galactofuranoside into the 5,6-O-[α-(dimethyl-amino)benzylidene] derivative, followed by acetylation of HO-2 and HO-3, and selective ring opening or the acetal, gave benzyl 2,3-di-O-acetyl-6-O-benzoyl-α β-D-galactofuranoside (4). The title disaccharide was synthesised from 4 by reaction with 3,4,6-tri-O-acetyl-α-D-galactofuranose 1,2-(methyl orthoacetate) followed by removal of protecting group

Acid-catalysed hydrolysis of 1,2-O-alkylidene-α-D-glucofuranoses

The rates of acid-catalysed hydrolysis of 1,2-O-alkylidene-alpha-D-glucofuranoses indicate that, for oligosaccharide synthesis, cyclopentylidene and cycloheptylidene acetals are better protecting groups than the isopropylidene residue. Hydrolysis was impeded by a nitrate group at position 5 and more so by one at position 3. The hydrolyses were accompanied by a positive drift in optical rotation, except for the 5-O-substituted compounds where the formation of D-glucopyranose derivatives cannot occur

The synthesis of 5-O-(2-acetamido-2-deoxy-α-D-glucopyranosyl)-β-D-glucofuranose

Condensation of dimeric 3,4,6-tri-O-acetyl-2-deoxy-2-nitroso-α-D-glucopyranosyl chloride (1) with 1,2-O-isopropylidene-α-D-glucofuranurono-6,3-lactone (2) gave 1,2-O-isopropylidene-5-O-(3,4,6-tri-O-acetyl-2-deoxy-2-hydroxyimino-α-D-arabino-hexopyranosyl)-α-D-glucofuranurono-6,3-lactone (3). Benzoylation of the hydroxyimino group with benzoyl cyanide in acetonitrile gave 1,2-O-isopropylidene-5-O-(3,4,6-tri-O-acetyl-2-benzoyloxyimino-2-deoxy-α-D-arabino-hexopyranosyl)-α-D-glucofuranurono-6,3-lactone (4). Compound 4 was reduced with borane in tetrahydrofuran, yielding 5-O-(2-amino-2-deoxy-α-D-glucopyranosyl)-1,2-O-isopropylidene-α-D-glucofuranose (5), which was isolated as the crystalline N-acetyl derivative (6). After removal of the isopropylidene acetal, the pure, crystalline title compound (10) was obtained

A facile preparation of alkyl α-glycosides of the methyl ester of N-acetyl-D-neuraminic acid

The reaction of methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-2-chloro-2,3,5-trideoxy-β-D-glycero-D-galacto-2-nonulopyranosonate with primary and secondary alcohols in the presence of silver salicylate affords, after O-deacetylation, stereo-specifically the corresponding methyl (alkyl 5-acetamido-3,5-dideoxy-α-D-glycero-D-galacto-2-nonulopyranosid)onates. The preparation of methyl(neopentyl 5-acetamido-3,5-dideoxy-α-D-glycero-D-galacto-2-nonulopyranosid)onate in benzene solution shows that this glycosylation can be carried out in an inert solvent