Synthesis and antitumor activity of sugar-ring hydroxyl analogues of daunorubicin.

Daunorubicin analogues in which the natural amino sugar, daunosamine, is replaced by neutral 2,6-dideoxy-hexopyranosyl residues have been prepared in high yields. Glycosidation of 3,4-di-O-acetyl-2,6-dideoxy-alpha-L-lyxo-hexopyranosyl chloride (13) with daunomycinone under Koenigs-Knorr conditions yielded exclusively the protected alpha-anomeric product 4, which was converted into the free glycoside 5. In contrast, the 1-chloro-D-ribo isomer 19, bearing p-nitrobenzoyl groups for hydroxyl-group protection, furnished a 5:3 mixture of the alpha (6) and beta (7) glycosides. Separation and individual deprotection afforded the target compounds 8 (from 6) and 9 (from 7). Whereas all of the D-ribo analogues (6--9) are inactive as antitumor agents in vivo against P388 lymphocytic leukemia in mice, the protected L-lyxo glycoside 4 (T/C 186) and also the free glycoside 5 (T/C 183) are highly effective in this test system; 5 is also active (T/C 146) in vivo against murine B16 melanocarcinoma.

New daunorubicin analogs. 3-Amino-2,3,6-trideoxy-alpha- and beta-D-arabino- and 3,6-diamino-2,3,6-trideoxy- alpha-D-ribo-hexopyranosides of daunomycinone.

Glycosidation of 2,3,6-trideoxy-3-trifluoroacetamido-4-O-trifluoroacetyl-alpha-D-arabino-hexopyranosyl chloride (19) (or the corresponding 4-p-nitrobenzoate, 20) with daunomycinone under Koenigs-Knorr conditions afforded, after separation of the anomers and removal of the protecting groups, the individual target glycosides 8 (alpha anomer; major product) and 9 (beta; minor) in acceptable yields. In contrast, the title diamino sugar, suitably protected with N-trifluoroacetyl and O-acetyl (or O-p-nitrobenzoyl) groups, underwent stereospecific coupling to the anthracycline aglycon by the glycal procedure to give, after deprotection, the alpha glycoside 12. All three analogs were assayed in vivo against P388 lymphocytic leukemia. They showed little (T/C 125 for 8; T/C 115 for 9) or no (compound 12) activity, but were essentially devoid of toxicity at the dose-levels tested.

Preparation of 3-amino-2,3,6-trideoxy-D-arabino-hexose hydrochloride and its N-trifluoroacetyl derivative.

Methyl 3-acetamido-4,6-O-benzylidene-2,3-dideoxy-alpha-D-arabino-hexopyranoside (5) was converted by treatment with N-bromosuccinimide into the 4-O-benzoyl-6-bromo derivative 6. Reduction with Raney nickel followed by catalytic transesterification of the resultant 4-benzoate 7 afforded methyl 3-acetamido-2,3,6-trideoxy-alpha-D-arabino-hexopyranoside (8), which could readily be converted into the 4-acetate 11. N-Decetylation of 7 and subsequent acid hydrolysis furnished 3-amino-2,3,6-trideoxy-D-arabino-hexose hydrochloride (9), the D enantiomorph of acosamine. The 3-benzamido analog (12) of 8 was prepared from 8 by N-deacetylation and subsequent benzoylation. Hydrolysis of 8 and 12 gave the 3-acetamido (10) and 3-benzamido (13) analogs of 9, which crystallized in the alpha anomeric form. 2,3,6-Trideoxy-3-trifluoro-acetamido-alpha-D-arabino-hexopyranose (15), a key intermediate for the synthesis of glycosidically coupled derivatives of 9, was obtained from 7 by saponification with barium hydroxide followed by N-trifluoracetylation of the resultant glycoside 14 and subsequent selective hydrolysis.

Preparative syntheses of 2,6-dideoxy-alpha-L-lyxo-hexose (2-deoxy-alpha-L-fucose) and its D-ribo epimer (digitoxose).

Methyl 4,6-O-benzylidene-2-deoxy-alpha-D-ribo-hexopyranoside (1) is converted into methyl 3,4-di-O-benzoyl-6-bromo-2,6-dideoxy-alpha-D-ribo-hexopyranoside (3) via the 3-O-benzoyl derivative (2) of 1 by subsequent treatment with N-bromosuccinimide. Compound 3 is the key intermediate in high-yielding, preparative syntheses of the title dideoxy sugars, which are constituents of many antibiotics, Dehydrohalogenation of 3 affords the 5,6-unsaturated glycoside 7, which undergoes stereospecific reduction by hydrogen with net inversion at C-5 to give methyl 3,4-di-O-benzoyl-2,6-dideoxy-beta-L-lyxo-hexopyranoside (8), whereas reductive dehalogenation of 3 provides the corresponding D-ribo derivative 4. The unprotected glycosides 9 (L-lyxo) and 5 (D-ribo) are readily obtained by catalytic transesterification, and mild, acid hydrolysis gives the crystalline title sugars 10 (L-lyxo) and 6 (D-ribo) in 45 and 57% overall yield from 1 without the necessity of chromatographic purification at any of the steps.

Reaction of derivatives of methyl 2,3-O-benzylidene-6-deoxy-alpha-L-mannopyranoside with butyllithium: synthesis of methyl 2,6-dideoxy-4-O-methyl-alpha-L-erythro-hexopyranosid-3-ulose.

Methyl 2,3-O-benzylidene-6-deoxy-alpha-L-mannopyranoside (2) reacted with butyllithium to give a mixture of 1,5-anhydro-3-C-butyl-1,2,6-trideoxy-L-ribo-hex-1-enitol (3) and its L-arabino analogue (4), together with methyl 2,3,6-trideoxy-alpha-L-erythro-hex-2-enopyranoside (5). In contrast, the 4-O-methyl-analogue (8) of 2 was converted by butyllithium into methyl 2,6-dideoxy-4-O-methyl-alpha-L-erythro-hexo-pyranosid-3-ulose (9), which was further characterized as its oxime 10. The 4-O-benzyl analogue of 8, obtained as two separate diastereoisomers (6 and 7) differing in configuration at C-2 of the dioxolane ring gave a complex misture of products on treatment with butyllithium.

Synthesis of 3-amino-2,3,6-trideoxy-D-ribo-hexose hydrochloride.

The title sugar, the 5-epimer of daunosamine, was prepared in a sequence of high-yielding steps from methyl alpha-D-mannopyranoside (1). Conversion of 1 into methyl 3-acetamido-4-O-benzoyl-6-bromo-2,3,6-trideoxy-alpha-D-ribo-hexopyranoside (2), followed by reduction with hydrogen and Raney nickel, gave the 4-benzoate (3) of methyl 3-acetamido-2,3,6-trideoxy-alpha-D-ribo-hexopyranoside (4). Saponification of 3 gave 4 as an oil that gave a crystalline 4-acetate (8). N-Deacetylation of 4 was effected with barium hydroxide, and the resultant glycoside was hydrolyzed to give 3-amino-2,3,6-trideoxy-D-ribo-hexose hydrochloride (7). The 3-benzamido analogue (5) of 4 was prepared from 4 by N-deacetylation and subsequent benzoylation, and hydrolysis of 5 gave crystalline 3-benzamido-2,3,6-trideoxy-D-ribo-hexose (6). The crystalline 3-acetamido analogue (9) of 6 was obtained by acid hydrolysis of the glycoside 4.

A preparative synthesis of 3-amino-2,3,6-trideoxy-L-lyxo-hexose (daunosamine) hydrochloride from D-mannose.

A simple, preparative route in nine steps from methyl alpha-D-mannopyranoside (1) is described that affords, in 40% overall yield, the title amino sugar 11, the sugar constituent of the antitumor antibiotics adriamycin and daunorubicin. The 2,3:4,5-dibenzylidene acetal (2) of 1 is converted by butyllithium into the 2-deoxy-3-ketone 3, whose oxime 4 is reduced with high stereoselectivity to the D-ribo amine, isolated as its N-acetyl derivative 5 and converted by action of N-bromosuccinimide into the 4-O-benzoyl-6-bromide 7. Dehydrohalogenation of gives the 5,6-unsaturated glycoside 8, which, after O-debenzoylation to 9, undergoes stereospecific reduction by hydrogen with net C-5 inversion to give the crystalline, N-acetylated methyl beta-glycoside (10) of daunosamine, readily converted into daunosamine hydrochloride (11) and into the crystalline N-benzoyl (14) and N-acetyl(15) derivatives. No chromatographic procedures for isolation are required in any of the steps.