Structurally Diverse Alkaloids from the Seeds of Peganum harmala

Investigation of the alkaloids from Peganum harmala seeds yielded two pairs of unique racemic pyrroloindole alkaloids, (±)-peganines A–B ( 1 – 2 ); two rare thiazole derivatives, peganumals A–B ( 3 – 4 ); six new β-carboline alkaloids, pegaharmines F–K ( 5 – 10 ); and 12 known analogues. Their structures, including stereochemistry, were elucidated through spectroscopic analyses, quantum chemistry calculations, and single-crystal X-ray diffraction. Notably, the incorporation of pyrrole and indole moieties in peganines A–B, thiazole fragments in peganumals A–B, and a C-1 α,β-unsaturated ester motif in pegaharmine F ( 5 ) are all rare, and their presence in the genus Peganum were demonstrated for the first time. All isolates were tested for antiproliferative activities against the HL-60, PC-3, and SGC-7901 cancer cell lines, and compounds 9, 11, 12, and 13 exhibited moderate cytotoxicity against HL-60 cancer cell lines with IC 50 values in the range of 4.36–9.25 μM.