Synthesis of Novel Conformationally Locked Carbocyclic Nucleosides Derived from 5,5- and 6,6-Bis(hydroxymethyl)bicyclo[2.2.1]heptan-2-ol

New carbocyclic N(6)-substituted adenine and pyrimidine nucleoside analogues with a bicyclo[2.2.1]heptane fragment as sugar moiety; synthesis, antiviral, anticancer activity and X-ray crystallography

New nucleoside analogues with an optically active bicyclo[2.2.1]heptane skeleton as sugar moiety and 6-substituted adenine were synthesized by alkylation of 6-chloropurine intermediate. Thymine and uracil analogs were synthesized by building the pyrimidine ring on amine 1. X-ray crystallography confirmed an exo-coupling of the thymine to the ring and an L configuration of the nucleoside analogue. The library of compounds was tested for their inhibitory activity against influenza virus A∖California/07/09 (H1N1)pdm09 and coxsackievirus B4 in cell culture. Compounds 13a and 13d are the most promising for their antiviral activity against influenza, and compound 3c against coxsackievirus B4. Compounds 3b and 3g were tested for anticancer activity.

Regio- and stereoselective synthesis of truncated 3'-aminocarbanucleosides and their binding affinity at the A3 adenosine receptor

The stereoselective synthesis of truncated 3'-aminocarbanucleosides 4a-d via a stereo- and regioselective conversion of a diol 9 to bromoacetate 11a and their binding affinity towards the human A(3) adenosine receptor are described.

Design, synthesis, and biological evaluation of novel coxsackievirus B3 inhibitors

The synthesis and SAR study of a novel class of coxsackievirus B3 (CVB3) inhibitors are reported. These compounds could be considered as the 6-chloropurines substituted at position 9 with variously substituted bicyclic scaffolds (bicyclo[2.2.1]heptane/ene-norbornane or norbornene). The synthesis and biological evaluation of 31 target compounds are described. Several of the analogues inhibited CVB3 in the low micromolar range (0.66-2muM). Minimal or no cytotoxicity was observed.

Synthesis of novel racemic carbocyclic nucleosides derived from 5,6-disubstituted norbornene

Novel class of the carbocyclic nucleosides based on bicyclo[2.2.1]heptene/heptane was prepared by two approaches. Thymine analogues were synthesized starting from methyl (1R*,4S*)-bicyclo[2.2.1]hepta-2,5-diene-2-carboxylate1by Michael addition of the thymine salt to the double bond as the key step. The yield and ratio of the isomers of this reaction depended on the used base (DBU, K2CO3). Purine nucleoside analogues were synthesized by the linear synthesis, the purine nucleobase was build-up on the amino group. The amino groups (exo/endoconfiguration) were introduced to the scaffold by the Curtius rearrangement. Norbornene analogues were converted to saturated andcis-hydroxylated nucleoside derivatives. [(1R*,2S*,3S*,4S*)-3-(6-Chloro-9H-purin-9-yl)bicyclo[2.2.1]hept-5-en-2-yl]methanol (13a) and [(1R*,2R*,3R*,4S*)-3-(6-chloro-9H-purin-9-yl)bicyclo[2.2.1]hept-5-en-2-yl]methanol (13b) showed moderate activity againstCoxsackievirus CVB3.

Synthesis of novel carbocyclic nucleoside analogues derived from 7-oxabicyclo[2.2.1]heptane-2-methanol

Hydroboration of [(1R*,2R*,4R*)-7-oxabicyclo[2.2.1]hept-5-en-2-yl]methyl benzoate (5), which was prepared by Diels–Alder reaction of furan with acrolein and subsequent reduction and benzoylation of the Diels–Alder product, afforded [(1R*,2S*,4S*,6S*)-6-hydroxy-7-oxabicyclo[2.2.1]heptan-2-yl]methyl benzoate (6) and [(1R*,2R*,4R*,5S*)-5-hydroxy-7-oxabicyclo[2.2.1]heptan-2-yl]methyl benzoate (7). The key intermediates, [(1R*,2S*,4S*,6R*)-6-hydroxy-7-oxabicyclo[2.2.1]heptan-2-yl]methyl benzoate (10) and [(1R*,2R*,4R*,5R*)-5-hydroxy-7-oxabicyclo[2.2.1]heptan-2-yl]methyl benzoate (11), were prepared from6and7, respectively, by oxidation with pyridinium dichromate and subsequent reduction of the thus obtained ketones. The Mitsunobu reaction of10and11with 6-chloropurine and subsequent reductive deprotection with diisobutylaluminium hydride afforded 6-chloropurine derivatives, which were converted to other purine analogues. Thymine analogues were prepared by Mitsunobu reaction of10and11with 3-benzoyl-5-methylpyrimidine-2,4(1H,3H)-dione and subsequent methanolysis. The target compounds were tested for the activity againstCoxsackievirus.

Synthesis of novel racemic carbocyclic nucleoside analogues derived from 4,8-dioxatricyclo[4.2.1.03,7]nonane-9-methanol and 4-oxatricyclo[4.3.1.03,7]decane-10-methanol, compounds with activity against Coxsackie viruses

(1R*,2R*,3R*,4S*)-7-Oxabicyclo[2.2.1]hept-5-ene-2,3-dimethanol (10) and (1R*,2R*,3R*,4S*)-bicyclo[2.2.2]oct-5-ene-2,3-dimethanol (14), which were prepared by the Diels–Alder reaction and subsequent reduction with lithium aluminium hydride, were treated with benzyl azidoformate to give benzylN-[(1R*,2R*,3S*,6S*,7S*,9S*)-9-(hydroxymethyl)-4,8-dioxatricyclo[4.2.1.03,7]nonan-2-yl]carbamate (11) and benzylN-[(1R*,2R*,3R*,6R*,7S*,10S*)-10-(hydroxymethyl)-4-oxatricyclo[4.3.1.03,7]decan-2-yl]carbamate (15). Hydrogenolysis of carbamates11or15afforded (1R*,2R*,3S*,6S*,7S*,9S*)-2-amino-4,8-dioxatricyclo[4.2.1.03,7]nonane-9-methanol (12) or (1R*,2R*,3R*,6R*,7S*,10S*)-2-amino-4-oxatricyclo[4.3.1.03,7]decane-10-methanol (16). The amines12and16were transformed to thymine and purine nucleoside analogues. The target compounds were tested for the activity againstCoxsackievirus.

Synthesis of Novel Carbocyclic Nucleoside Analogues Containing Bicyclo[2.2.1]hept-2-ene-2-methanol

Starting ethyl (1R*,2R*,3R*,4S*)-3-bromobicyclo[2.2.1]hept-5-ene-2-carboxylate (9) was reduced with LiAlH4and benzoylated giving [(1R*,2R*,3R*,4S*)-3-bromobicyclo[2.2.1]hept-5-en-2-yl]methyl benzoate (11). Treatment of11with NaN3and CrO3in acetic acid afforded [(1R*,2S*,3R*,4R*,5S*,6R*)-6-azido-3-bromo-5-hydroxybicyclo[2.2.1]hept-2-yl]methyl benzoate (12a) and [(1R*,2S*,3S*,4R*,5S*,6R*)-5-azido-3-bromo-6-hydroxybicyclo[2.2.1]heptan-2-yl]-methyl benzoate (12b). These key intermediates were separated and converted in five reaction steps to (1R*,2R*,3S*,4S*)-3-[(5-amino-6-chloropyrimidin-4-yl)amino]-5-(hydroxymethyl)- bicyclo[2.2.1]hept-5-en-2-ol (17a) and (1R*,2R*,3S*,4S*)-3-[(5-amino-6-chloropyrimidin-4-yl)- amino]-6-(hydroxymethyl)bicyclo[2.2.1]hept-5-en-2-ol (17b). Ring closure with triethyl orthoformate led to (1R*,2R*,3S*,4S*)-5-(chloromethyl)-3-(6-chloro-9H-purin-9-yl)bicyclo[2.2.1]hept-5-en-2-ol (18a) and (1R*,2R*,3S*,4S*)-6-(chloromethyl)-3-(6-chloro-9H-purin-9-yl)- bicyclo[2.2.1]hept-5-en-2-ol (18b) using hydrochloric acid as a catalyst or (1R*,2R*,3S*,4S*)-3-(6-chloro-9H-purin-9-yl)-5-(hydroxymethyl)bicyclo[2.2.1]hept-5-en-2-ol (19a) and (1R*,2R*,3S*,4S*)- 3-(6-chloro-9H-purin-9-yl)-6-(hydroxymethyl)bicyclo[2.2.1]hept-5-en-2-ol (19b) using trifluoro- acetic acid as a catalyst. From19aand19b, 6-amino- and 6-(cyclopropylamino)purine derivatives20and21were prepared.

Synthesis of Novel Carbocyclic Nucleoside Analogues Derived from 2-(Hydroxymethyl)bicyclo[2.2.1]heptane

The key intermediates, [(1R*,2R*,4R*,6R*)-6- (12a) and [(1R*,2R*,4R*,5S*)-5-(hydroxymethyl)- bicyclo[2.2.1]heptan-2-yl]methyl benzoates (12b), were prepared from (1R*,2S*,4R*)- bicyclo[2.2.1]hept-5-en-2-ylmethyl benzoate by hydroboration, oxidation with pyridinium dichromate and subsequent reduction of the thus obtained ketones. The Mitsunobu reaction of12aand12bwith 6-chloropurine afforded 6-chloropurine derivatives, which were converted into others purine analogues. Thymine analogues were prepared from [(1R*,2R*,4S*,6S*)-6- (25a) and [(1R*,2S*,4R*,5S*)-5-aminobicyclo[2.2.1]heptan-2-yl]methanols (25b), which were prepared from alcohols12aand12bin several easy steps.

Synthesis of Novel Carbocyclic Nucleosides and Pro-Tides Derived from 4-Oxatricyclo[4.2.1.03,7]nonane-9-methanol

(1R*,2R*,3R*,6R*,7S*)-2-Amino-4-oxatricyclo[4.2.1.03,7]nonane-9-methanol (9) was prepared from (1R*,2R*,3R*,4S*)-bicyclo[2.2.1]hept-5-ene-2,3-dimethanol by treatment with benzyl azidoformate followed by hydrogenolysis. The amine9was transformed to thymine and purine nucleoside analogues. The prepared analogues were converted to corresponding Pro-Tides by treatment with methylN-[chloro(phenoxy)phosphoryl]-L-alaninate in the presence of 1-methylimidazole ortert-butylmagnesium chloride.

Synthesis of Novel Conformationally Locked Carbocyclic Nucleosides Derived from 3-(Hydroxymethyl)bicyclo[2.2.1]heptane-2,5-diol

(1R*,2R*,3R*,4R*,5R*,6S*)-3-Amino-5-(benzyloxy)-6-(hydroxymethyl)bicyclo[2.2.1]heptan-2-ol (18) was prepared in seven easy steps from benzyl (1R*,2S*,3S*,4S*)-3-(benzyloxy)bicyclo[2.2.1]hept-5-ene-2-carboxylate (10). Reaction of amine18with ethylN-((2E)-3-ethoxymethacryloyl)carbamate afforded 1-[(1R*,2R*,3R*,4R*,5S*,6R*)-6-(benzyloxy)-3-hydroxy-5- (hydroxymethyl)bicyclo[2.2.1]heptan-2-yl]-5-methylpyrimidine-2,4(1H,3H)-dione (21) and after deprotection by transfer hydrogenation, free thymine analogue22. The thymine derivative21was converted to 2,3'-anhydronucleoside26. Treatment of the benzyl derivative18with sodium in liquid ammonia led to amine19, which was used as key intermediate for the construction of (1R*,2R*,3R*,4R*,5R*,6S*)-3-(6-chloro-9H-purin-9-yl)-6-(hydroxymethyl)-bicyclo[2.2.1]heptane-2,5-diol (28) and (1R*,2R*,3R*,4R*,5R*,6S*)-3-(2-amino-6-chloro-9H-purin-9-yl)-6-(hydroxymethyl)bicyclo[2.2.1]heptane-2,5-diol (33). Ammonolysis of28led to 6-amino-9H-purine derivative29. 6-(Dimethylamino)-9H-purine analogue30and 6-(cyclopropylamino)-9H-purine analogues31and34were prepared by aminolysis of corresponding chloropurine derivatives.

Synthesis of Novel Racemic Conformationally Locked Carbocyclic Nucleosides Derived from 7-Substituted Bicyclo[2.2.1]hept-5-ene-2,2-dimethanols

(1R*,4R*,7S*)-7-Aminobicyclo[2.2.1]hept-5-ene-2,2-dimethanol (15) was prepared in four easy steps from bicyclo[2.2.1]hept-5-ene-2,2-dimethanol (10). Reaction of amine 15 with ethyl N-((E)-3-ethoxymethacryloyl)carbamate afforded thymine derivatives 17a. The amine 15 was used to construct 6-chloro-9H-purine derivative 19a, 2-amino-6-chloro-9H-purine derivative 22a. Ammonolysis of 19a led to the adenine derivative 20a. Treatment of 22a with trifluoroacetic acid afforded guanine nucleoside 23a. (1R*,4R*,7S*)-7-[6-(Cyclopropylamino)-9H-purin-9-yl]bicyclo[2.2.1]hept-5-ene-2,2-dimethanol (21a) and (1R*,4R*,7S*)-7-[2-amino-6-(cyclopropylamino)-9H-purin-9-yl]bicyclo[2.2.1]hept-5-ene-2,2-dimethanol (24a) were prepared by aminolysis of 19a and 22a. Saturated nucleosides 17b, 20b, 21b, 23b, 24b were obtained by hydrogenation on palladium catalyst.