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Novel structure-activity relationships (SAR) distinct from known SAR for ellipticines have been revealed for certain ellipticinium salts. In particular, ellipticiniums such as the prototypical 9-methoxy-2-methylellipticinium (I- or OAc-) were found to be preferentially cytotoxic to the brain tumor cell line subpanel of the NCI 60 cell-line screening panel. Similar specificity also was apparent with 9-unsubstituted ellipticiniums, or others bearing 9-methyl or 9-chloro substituents. In contrast, 9-hydroxy-substituted ellipticiniums, as well as all nonquaternized ellipticines tested, were devoid of brain tumor specificity. Therefore, it did not appear that this unusual preference was correlated with the relative availability of redox cycling mechanisms, since redox cycling presumably is blocked in 9-methyl- and 9-chloroellipticiniums. Indeed, related investigations have indicated that the brain tumor specificity is mediated by preferential uptake and intracellular accumulation of the specific ellipticiniums. The present study further supports that the NCI in vitro "disease-oriented" primary screen can facilitate the discovery of novel, selectively cytotoxic leads for in vivo and mechanistic investigations.

Reductive N,N-dialkylation of daunorubicin with 2,2'-oxydiacetaldehyde and NaBH3CN occurred in two steps without interruption and with cyclization to form 3'-(4-morpholinyl)-3'-deaminodaunorubicin. This derivative retained the antitumor efficacy of doxorubicin against mouse leukemia P388 but at one-fortieth the dose; hence, it is the most potent anthracycline analogue synthesized so far. The 4-methoxy-1-piperidinyl derivative, similarly prepared with 3-methoxyglutaraldehyde, showed improved efficacy against P388, though at normal doses. Results with a series of analogues indicate that incorporation of the N in the new ring and the presence of an ether O at the 4-position are critical for enhanced activity.

Treatment of doxorubicin with formaldehyde and NaCN afforded the N-(cyanomethyl) derivative as a stable alpha-cyanoamine with but moderate antitumor activity in mice, although it was prototypal to the intensely potent alpha-cyanomorpholine derivative. 2-Methoxyacetaldehyde and NaCN afforded the N-(2-methoxy-1-cyanoethyl) derivative as an open-chain analogue of the cyanomorpholine. This analogue underwent rapid hydrolysis to doxorubicin and appeared to act as a prodrug, giving increased antitumor efficacy although with decreased potency. N-(Carboxymethyl)daunorubicin was a highly water-soluble but inactive analogue, synthesized by N-alkylation with ethyl iodoacetate and saponification. The similar N-alkylation of N-(cyanomethyl) daunorubicin demonstrated the combining of N-alkyl chains having different functional substituents.

The C-glycosyl isostere of 4-demethoxy-9-desacetyldaunorubicin and its 7,9-diepi isomer have been synthesized via Diels-Alder reaction of a protected daunosaminyl-2,4-pentadiene with quinizarin quinone.

Treatment of daunorubicin with methanolic ammonia affords 5-iminodaunorubicin, the first quinone-modified analogue of either daunorubicin or adriamycin. This product retains antileukemic activity in mice, is less cardiotoxic by electrocardiographic measurements in rats, and is nonmutagenic in Salmonella typhimurium (Ames test).

Stereospecific coupling of a pentadienyl chain to C.1 of daunosamine followed by Diels-Alder reactions with quinones gave a new synthesis of C-glycosides, including the first intermediates to anthracycline C-glycosyl isosteres.

3'-Deamino-3'-(3-cyano-4-morpholinyl)doxorubicin is a new analogue that is 100 to 1000 times more potent than doxorubicin against tumors in cell culture or in mice, that is active by intraperitoneal, intravenous, or oral dosing, and that does not produce chronic myocardial lesions in mice. This analogue was encountered in studies on the reductive alkylation of doxorubicin and daunorubicin with 2,2' - oxybis [acetaldehyde], which constructs a morpholino ring incorporating the amino N. The morpholinyl nitrile byproducts are separated by virtue of their nonbasicity from the expected morpholino derivatives. The 13-dihydro and 5-imino derivatives are also described in this important new class of anthracyclines.

The 3-(hydroxymethyl) branched homologue of 2-deoxyribofuranose was synthesized from the corresponding branched ribofuranose 2-O-(S-methyl dithiocarbonate) with tributyltin hydride in the first direct, one-step deoxygenation at C-2 of a ribofuranose. Nucleoside coupling afforded the corresponding 3'-branched 2'-deoxyribonucleosides of thioguanine. The alpha- and beta-nucleosides were equally inhibitory to growth of WI-L2 human lymphoblastoid cells, were phosphorylated and incorporated into the DNA of Mecca lymphosarcoma in mice to the same degree, and were more effective in these tests than the parent analogue alpha-2'-deoxythioguanosine. These results indicate that the hydroxy functions at the 3' and 5' positions of 2'-deoxynucleosides are interchangeable and that acceptance by the that the furanose ring oxygen and 2'-methylene are corresponding interchangeable, and that acceptance by the enzymes is improved if primary hydroxyls are provided at both the 3' and 5' positions.

One-step treatment of daunomycinone with excess 2-aminoethanethiol and 2-aminoethanol in trifluoroacetic acid afforded at C-7 the thioether (77% yield) and ether (30% after recycling), respectively. Stereoselectivity for the natural 7S over the 7R configuration was greater for the ether (97:3) than for the thioether (2.5:1). Esterification of daunomycin at C-7 with beta-alanine was accomplished through the mixed anhydride of Z(OMe)-beta-alanine. Preliminary biological tests suggests that the antitumor and DNA interactive properties of the anthracyclines can be retained in such structures.

Previously we reported that reductive alkylation of doxorubicin with 2,2'-oxybis[acetaldehyde] and NaBH3CN to form the 4''-morpholinyl derivative also gave the intensely potent 3''-cyano-4''-morpholinyl as a byproduct, by addition of CN- to an iminium intermediate in place of hydride. We now find that sugar 4'-OH is a third nucleophile that can add to the iminium intermediate in this reaction. Bridging of the 4'-OH to the morpholine ring at C.5'' formed a novel byproduct with an oxazolidino ring fused to the sugar and morpholine. The new product was minor at neutral pH but predominant at an acidic pH. When tested against tumors in mice it was 4-6 times more potent than doxorubicin. Hence, in comparison with the 3''-cyano-4''-morpholinyl, potency was reduced up to 100-fold by the O bridge. Analytical HPLC showed the presence of three of the four possible diastereoisomers, and two were isolated. The diastereoisomers appeared to differ in stability. In vitro tests suggested that biological potency varied inversely with stability.

In the first approach by total synthesis to the structure of the antitumor antibiotic septacidin, analogues have been obtained which show similar inhibition of RNA-DNA synthesis in cultured leukemia L1210 cells and similar activity against transplanted leukemia P388 in mice. In these analogues, the natural aminoheptose moiety is replaced by 4-amino-4-deoxy-and 4-amino-4,6-dideoxy-L-glucose, to retain the natural configuration of the pyranose ring. Also retained is the lipophilic fatty acid-amino acid side chain attached to the 4-amino group and glycosylation at the 6-NH2 of adenine. If the fatty acid chain was shortened from C16 to C6, if the fatty chain was shifted to the glycine unit, or if the glycine unit was omitted, activity was completely lost. However, activity was retained if the C16 chain was shortened only to C12 or if the glycine unit was extended to beta-alanine. Both active and inactive analogues were nonbinding to DNA and nonmutagenic to Salmonella strains. The synthetic approach was to start with a suitably protected sugar (L-fucose and L-galactose), construct the adenine moiety at C-1 introduce a 4-amino group, and finally attach the preformed side chain.