Synthesis of 4‐Octuloses. Part 6. 4‐Octulose Derivatives, Prepared from L‐Sorbose, as Key Intermediates in the Stereoselective Synthesis of C‐Glycoside and Polyhydroxyindolizidine Analogues.
Reactions of 1 and 12 with p-toluenesulfonyl chloride in pyridine gave the corresponding 1-O-p-toluenesulfonyl derivatives 2 and 13 in yields of 91% and 60%, respectively. Compound 12 was also transformed into 14 by treatment with I2/ Ph3P/imidazole in anhydrous dichloromethane. Treatment of compounds 12 and 13/14 with NaN3 in DMF furnished the respective 1-azido-1-deoxy derivatives 3 and 15, which were then deacetonated to give the free 4-octuloses 4 and 16. These were subsequently hydrogenated in the presence of 10% Pd/C to afford the expected polyhydroxylated branched-chain pyrrolidines 5 and 17. Attempted OH R
4‐Octulose Derivatives, Prepared from L‐Sorbose, as Key Intermediates in the Stereoselective Synthesis of C‐Glycoside and Polyhydroxyindolizidine Analogues
Reactions of 1 and 12 with p-toluenesulfonyl chloride in pyridine gave the corresponding 1-O-p-toluenesulfonyl derivatives 2 and 13 in yields of 91% and 60%, respectively. Compound 12 was also transformed into 14 by treatment with I2/Ph3P/imidazole in anhydrous dichloromethane. Treatment of compounds 12 and 13/14 with NaN3 in DMF furnished the respective 1-azido-1-deoxy derivatives 3 and 15, which were then deacetonated to give the free 4-octuloses 4 and 16. These were subsequently hydrogenated in the presence of 10% Pd/C to afford the expected polyhydroxylated branched-chain pyrrolidines 5 and 17. Attempted OH OMes transformation at C-8 in the N−Cbz-protected pyrrolidines 7 and 19 was unsuccessful and an internal anhydration process took place to yield the corresponding C-glycoside-like furanoses 9 and 20. On the other hand, 23 was transformed into the D-ribo analogue 25 through reduction of the intermediate 4,6-diulose 24. Finally, deprotection of 25 in acid medium to give the free 4-ulose 26, followed by hydrogenation of the latter in the presence of 10% Pd/C in methanol, allowed the preparation of (6S,7S,8S,8aS)-6,7,8-trihydroxy-8a-methoxyindolizidin-3-one (27).
Synthesis of 1-deoxy-6-epicastanospermine and 1-deoxy-6,8a-diepicastanospermine.
Extension of the carbon spine of 2,3;4,5-di-O-isopropylidene-beta-D-fructopyranoside by oxidation at C-1 followed by a Wittig reaction using the phosphorane Ph3P = CHCO2Et gave an oct-4-ulose derivative, which was then transformed into the key intermediate 1-azido-1,2,3-trideoxy-D-arabino-oct-4-ulose. Catalytic hydrogenolysis of this azide, followed by reductive amination between the resulting 1-amino substituent and the 4-keto-group then gave a mixture of pyrrolidines. After sulphonylation at the terminal 8-position, the pyrrolidines were then cyclised further between the nitrogen and C-8 to give 1-deoxy-6-epicastanospermine and 1-deoxy-6,8a-diepicastanospermine.