Agelasine E, previously isolated from the marine sponge Agelas nakamurai, has been synthesized for the first time, together with analogs with various terpenoid side chains. Treatment of N6-methoxy-9-methyl-9H-purin-6-amine with allylic bromides gave the desired 7,9-dialkylpurinium salts together with minor amounts of the N6-alkylated isomer. The N6-methoxy group was finally removed reductively. 1H-15N HMBC and 1H-15N HSQC NMR spectroscopy gave additional information on tautomerism and charge delocalization in the purine derivatives studied. The heterocyclic products were screened for activity against Mycobacterium tuberculosis and agelasine analogs carrying a relatively long terpenoid substituent in the purine 7-position and a methoxy group at N-6 were potent inhibitors of bacterial growth. Since agelasine analogs with the geranylgeranyl chain at N-7 exhibited antimicrobial activity, several strategies for synthesis of geometrically pure (2E,6E,10E)-geranylgeranyl bromide from geranyllinalool were evaluated.

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9-Aryl-, 9-arylsulfonyl- and 9-benzyl-6-(2-furyl)purines were synthesized by N-alkylation or N-arylation of the purine followed by Stille coupling to introduce the furyl substituent in the 6-position and the compounds screened for activity against Mycobacterium tuberculosis. The 9-aryl- and 9-sulfonylarylpurines exhibited weak activity toward the bacteria, but 9-benzylpurines were good inhibitors especially those carrying electron-donating substituents on the phenyl ring. A chlorine atom in the purine 2-position further enhanced activity. The high antimycobacterial activity (MIC 0.39 microg/mL against M. tuberculosis), low toxicity against mammalian cells and activity inside macrophages found for 2-chloro-6-(2-furyl)-9-(4-methoxyphenylmethyl)-9H-purine makes this compound a highly interesting potential antituberculosis drug.

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