New macrocyclic spermine (budmunchiamine) alkaloids from Albizia gummifera: with some observations on the structure--activity relationships of the budmunchiamines.

The CH2Cl2 extract of the stem bark of Albizia gummifera yielded four macrocyclic spermine alkaloids (budmunchiamines), three of them being new analogues. On the basis of spectral analysis and comparison with related compounds they were identified as budmunchiamine G (1) and the new analogues budmunchiamine K (2), 6'xi-hydroxybudmunchiamine K (3), and 9-normethylbudmunchiamine K (4). The four isolated alkaloids and other related budmunchiamines isolated from Albizia schimperana were all active against two Gram-positive and two Gram-negative bacteria at MIC levels below 80 micrograms mL(-1), and showed toxicity to brine shrimp larvae (with LC50 values below 100 micrograms mL(-1)). The negative impact of side chain hydroxylation and N-demethylation on both measures of biological activity was shown to be considerable.