High-Resolution LC-MS/MS Characterization of Budmunchiamine-Type Alkaloids in Albizia niopoides

Budmunchiamines are macrocyclic spermine alkaloids that constitute a distinctive class of polyamine natural products predominantly found in species of the genus Albizia. Comprehensive characterization of these compounds remains challenging because of their structural diversity and the limited availability of reference standards. This study aimed to profile the budmunchiamine alkaloids present in the trunk bark of Albizia niopoides using high-resolution tandem mass spectrometry.

Alkaloids were extracted from the trunk bark of A. niopoides and analyzed by ultrahigh-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight mass spectrometry (UHPLC-ESI-QTOF-MS) operated in positive ionization mode. Compound annotation was based on accurate mass measurements (≤ 5 ppm), chromatographic retention behavior, isotopic patterns, and diagnostic MS/MS fragmentation, supported by comparison with published data.

Twenty-six macrocyclic spermine alkaloids were detected and annotated. The MS/MS spectra consistently exhibited characteristic budmunchiamine fragment ions at m/z 214, 171, 169, and 129, together with diagnostic neutral losses, confirming assignment to this structural class. Six compounds were identified as the known budmunchiamines L1, L4, L5, and L6, whereas two corresponded to previously synthesized analogues (Compounds 2 and 21). The remaining 20 compounds displayed distinct precursor ions but closely related fragmentation pathways, indicating previously unreported budmunchiamine-type analogues.

UHPLC-ESI-QTOF-MS/MS proved to be an effective strategy for the dereplication and structural annotation of macrocyclic spermine alkaloids from A. niopoides. The results substantially expand the known chemical diversity of budmunchiamines in this species and demonstrate the value of high-resolution tandem mass spectrometry for the characterization of structurally complex natural products.