Dear Sir,
EI MS and ESI MS studies of the bisesquiterpene from cotton seeds -Gossypol and its Aza-derivatives
Gossypol (GOS) is a yellow bisesquiterpene isolated from cotton plants. 1 Great biological activity of GOS has attracted the attention of many scientists in the world. This polyphenol is characterized by anticancer, 2,3 antimicrobial, 4,5 antifungal, 6 and antiviral 7,8 activity as well as active in inhibiting spermatogenesis. 9 Despite many useful biological properties, GOS cannot be applied directly in medical therapy because of its relatively high toxicity, evoked mainly by the presence of two aldehyde groups. 10 One of the convenient ways to decrease the GOS toxicity and enhance its useful biological properties is to transform it into its aza-derivatives, e.g. Schiff bases or hydrazones. Up to now, a large number of GOS derivatives of this type have been synthesized, investigated, and considered as potential therapeutic agents against many diseases like malaria, lung cancer, or HIV1. 11,12 Despite the synthesis of many Schiff bases and hydrazones of GOS, their full characterization by mass spectra and the fragmentation pathways have not been performed till now. We propose here the fragmentation pathways of GOS and its seven representative derivatives (Scheme 1) on the basis of lowand high-resolution EI MS and ESI MS spectra.
GOS was extracted from cotton seeds of Gossypium Herbaceum, 13 whereas its Schiff bases G1-G7 were synthesized following the procedures described in Refs 14-18, respectively.
The EI MS data of GOS and its derivatives (G1-G5, G7) as well as its hydrazone (G6) are displayed in Table 1. On the basis of low-resolution EI mass spectra, exact mass measurements and also B/E and B 2 /E linked scan spectra, the principal mass spectral fragmentation routes of GOS and G1-G7 are proposed in Schemes 2 and 3. In the EI MS spectrum of GOS, no peak of molecular ion is observed, whereas the highest positioned peak is found at m/z 500. This peak is of a very low relative intensity and can be assigned to the odd-electron fragment ion b, formed from the molecular ion by the loss of one water molecule. Furthermore, in the EI spectrum of GOS, three other characteristic peaks appear at m/z 467, 454, and