Synthesis of daunorubicin peptide conjugates

Duy Nhu Nguyen, Purdue University

Abstract

The conjugation of daunorubicin, a red pigment first isolated from Streptomyces peucetius, exhibiting a wide range of antitumor activity, to peptide using different linker arms is detailed. The methyl ketone (C14 center) was activated by converting to the bromomethyl ketone followed by reacting with potassium 3-mercaptopropanoate, in the presence of 18-crown-6 to give 14- ((carboxyethyl)thio) -3$\sp\prime$-N-trifluoroacetyldaunorubicin. This derivative was converted into the active ester and then successfully coupled with the different peptides. The reaction of the C13 carbonyl with hydrazine monohydrate, ethylenediamine, $\beta$-alanine ethyl ester, and ammonium acetate failed to give the desired product. Amination with 4-hydrazinobenzoic acid afforded the desired compound, 13- ((carboxyphenyl)hydrazono) -3$\sp\prime$-N-trifluoroacetyldaunorubicin. The conversion to active ester was successful, unfortunately, it could not be coupled to any peptide. Different active esters such as pentafluorophenol and HOBt were prepared but the conjugation also failed. Daunorubicin was successfully linked to aminooxyacetic acid hemihydrochloride. The 13- ((carboxymethyl)oxime) -3$\sp\prime$-N-trifluoroacetyldaunorubicin was converted into the active ester and coupled to the peptides without any problem. The C4$\sp\prime$ hydroxyl group was converted to the 4$\sp\prime$-epimer. It was further transformed into the triflate and tosylate derivatives. The reaction of these derivatives with various nucleophilic linker arms failed to give any desired product. The 3$\sp\prime$-N-trifluoroacetyldaunorubicin was allowed to react with succinic anhydride to afford the 4$\sp\prime$-succinyl-3$\sp\prime$-N-trifluoroacetyldaunorubicin. This derivative was successfully converted into the active ester and coupled with the peptides. The reaction of 3$\sp\prime$-N-allocdaunorubicin with succinic anhydride did not give the desired product because the alloc group was too bulky, thus preventing the reagents from reacting. The daunorubicin-AAAYGGFL and daunorubicin-YGGFL conjugates were tested for their binding affinity using radioimmunoassay. The antibody did not recognize the conjugates. In vitro binding assay showed that the C4$\sp\prime$ and to a minor extent the C14 conjugates exhibited good binding affinity. As expected, the conjugates did not have good cytotoxicity because of their N-trifluoroacetylation.

Degree

Ph.D.

Advisors

Byrn, Purdue University.

Subject Area

Pharmacology|Organic chemistry

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