Synthesis of novel thiazole-based 8,9-dihydro-7H-pyrimido[4,5-b][1,4]diazepines as potential antitumor and antifungal agents

• New series of pyrimido[4,5-b][1,4]diazepines were synthesized from caffeine.
• All diazepines were obtained with high regioselectivity.
• Compounds 7d and 7g showed important antitumor activity with GI50 0.35–2.98 μM.
• Antifungal activity was performed against C. albicans and C. neoformans.
• Diazepines 7a and 7b exhibited high activity against clinical isolated C. neoformans.

A new series of novel thiazole-based 8,9-dihydro-7H-pyrimido[4,5-b][1,4]diazepines 6a–g and 7a–g were obtained with high regioselectivity from the reaction of triamino- or tetraaminopyrimidines 4 and 5 with α,β-unsaturated carbonyl compounds 3a–g based on 2,4-dichlorothiazol-5-carbaldehyde 1. Twelve of the synthesized compounds were selected and tested by US National Cancer Institute (NCI) for their antitumor activity against 60 different human tumor cell lines. Compounds 7d and 7g showed important GI50 ranges of 1.28–2.98 μM and 0.35–2.78 μM respectively under in vitro assays. In addition, 6a–g and 7a–g were tested for antifungal properties against the clinical important fungi Candida albicans and Cryptococcus neoformans. Although these compounds showed moderate activities against C. albicans, the 2-amino derivatives 7a–g and mainly 7a and 7b, showed high activity against standardized and clinical isolates of C. neoformans with MIC50 = 7.8–31.2 μg/mL, MIC80 = 15.6–31.2 μg/mL and MIC100 = 15.6–62.5 μg/mL. In addition, since both compounds were fungicide rather than fungistatic these thiazole-based 8,9-dihydro-7H-pyrimido[4,5-b][1,4]diazepines appear as good candidates for further development not only as antifungal but also as antitumor drugs.

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