The crystal structures of three anti-HIV 3'-azido-3'-deoxynucleosides have been determined to gain conformational information for structure-activity studies. The compounds 3'-azido-3'-deoxythymidine (AZT), 3'-azido-2',3'-dideoxyuridine (CS-87), and 3'-azido-2',3'-dideoxy-5-ethyluridine (CS-85) are all active inhibitors of HIV-1 replication. X-ray diffraction data for all three compounds were measured at 165 K.

L-nucleosides selectively enter malaria infected erythrocytes and have the unique ability to be metabolised by the malarial adenosine deaminase. This has allowed us to design novel L-nucleosides as potential anti-malarials.

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The L-stereoisomer analogues of D-coformycin selectively inhibited P. falciparum adenosine deaminase (ADA) in the picomolar range (L-isocoformycin, Ki 7 pM; L-coformycin, Ki 250 pM). While the L-nucleoside analogues, L-adenosine, 2,6-diamino-9-(L-ribofuranosyl)purine and 4-amino-1-(L-ribofuranosyl)pyrazolo[3,4-d]-pyrimidine were selectively deaminated by P. falciparum ADA, L-thioinosine and L-thioguanosine were not. This is the first example of 'non-physiological' L-nucleosides that serve as either substrates or inhibitors of malarial ADA and are not utilised by mammalian ADA.