Factors determining the performance of triple quadrupole, quadrupole ion trap and sector field mass spectrometers in electrospray ionization tandem mass spectrometry of oligonucleotides. 1. Comparison of performance characteristics

The performance of triple-stage quadrupole (TSQ), quadrupole ion trap (QIT), and double focusing sector field (DFSF) mass spectrometers for the generation of fragment ions to obtain sequence information about oligonucleotides was compared. Upon electrospray ionization (ESI), the charge-state distribution of candidate precursor ions not only varied significantly with the type of mass spectrometer, but also with the size and sequence of the investigated oligonucleotides. While concentration limits of detection for an octanucleotide were in the 100 pmol/L range on the QIT and in the 5-10 nmol/L range on the TSQ and DFSF instruments, those of a 24-mer were in the 2-13 nmol/L range on all three instruments. Reproducibility of mass determination, an important prerequisite for reliable identification of fragment ions, was highest on the TSQ with 0.0037% relative standard deviation over three days. Finally, the tandem mass spectra of a dimethoxytritylated pentanucleotide recorded on the three instruments were compared. Relatively simple spectra dominated by complete series of fragment ions of the (a-B) and w type were obtained on the QIT. Complete series of (a-B) and w ions were also observed on the TSQ. However, additional fragments belonging to the b, c, d, x and z series were found in the spectrum. In the spectrum recorded after in-source fragmentation in the DFSF, only fragments corresponding to the loss of a nucleobase and a complete series of w ions were observed. All three mass spectrometers were suitable for the generation of fragment ions, from which the complete nucleotide sequence of the pentanucleotide could be deduced.

New taxonomically significant sesquiterpenoids from Leontodon autumnalis

The methanolic extract of subaerial parts of Leontodon autumnalis afforded four new and two known sesquiterpenoids of the guaiane type. The known compounds were identified by means of (1)H and (13)C NMR spectroscopy as crepidiaside A (1) and B (2). The structures of the new compounds were determined by extensive 1D and 2D NMR experiments as 15-glucopyranosyloxy-2-oxo-guaia-3,11(13)-dien-1alp ha,5alpha, 6beta,7alpha,10alphaH-12,6-olide (3); 15-glucopyranosyloxy-2-oxo-guai-3-en-1alpha,5alpha+ ++,6beta,7alpha, 10alpha,11betaH-12,6-olide (4); 15-hydroxy-2-oxo-guai-3-en-1alpha, 5alpha,6beta,7alpha,10alpha,11betaH-12,6-+ ++olide (5); and 15-glucopyranosyloxy-2-oxo-guaia-3,11(13)-dien-1bet a,5alpha,6beta, 7alpha,10alphaH-12,6-olide (6), respectively. HPLC-DAD and HPLC-MS analyses of crude extracts of subaerial parts of 25 different taxa of the genus Leontodon revealed that compounds 1 and 2 occur in all investigated members of the section Oporinia (L. autumnalis, L. croceus, L. helveticus, L. montaniformis, L. montanus, L. pyrenaicus, and L. rilaensis) and in L. duboisii from the section Kalbfussia. Compounds 1-6 are detectable neither in other investigated taxa of Kalbfussia (L. cichoraceus, L. muelleri, and L. palisae) nor in any members of the subgenus Leontodon. Compounds 3-5 occur in high amounts only in L. croceus and L. pyrenaicus and in samples of L. autumnalis from northwestern Europe. In other members of the section Oporinia, in L. duboisii as well as in samples of L. autumnalis from the Pyrenees, the Alps, the Carpathians, and southern Central Europe, these substances occur only in trace amounts; in L. montanus and its closest relatives, compounds 3-5 are not detectable at all. Compound 6 is only detectable in samples of L. autumnalis, L. helveticus, L. pyrenaicus, L. rilaensis, and L. duboisii.

Isolation and characterization of methoxylated flavones in the flowers of Primula veris by liquid chromatography and mass spectrometry

Characterization of six flavones, which were named substances G1, G2, G3, G4, G5 and G6 according to their R(F) values in normal-phase thin-layer chromatography, is reported. The pure flavones were purified after maceration with methanol by normal-phase solid-phase extraction, normal-phase medium-pressure liquid chromatography, normal-phase preparative thin-layer chromatography and preparative reversed-phase high-performance liquid chromatography (RP-HPLC). The collected fractions of several isolation steps were analyzed by normal-phase (NP) and RP-HPLC. Detection and identification of the substances G was accomplished by UV detection at 213-216 nm, diode array UV detection, or fluorescence detection (lambda(ex)=330 nm; lambda(cm)=440 nm). The molecular mass, the elementary composition, and the structure of the six components was determined by electron-impact high-resolution mass spectrometry (EI-HRMS). Substance G4 was identified as 3',4',5'-trimethoxyflavone. The substances G1-G6 were shown to be mono-, di- tri- and pentamethoxyflavones. HPLC-electrospray ionization tandem mass spectrometry (ESI-MS-MS) of the flavones was carried out employing a 150x2 mm I.D. column packed with a 3 microm/100 A octadecylsilica stationary phase and a mobile phase comprising 1.0% acetic acid in water-acetonitrile (50:50). Comparative RP-HPLC-ESI-MS of the raw methanol extract and the isolated substances G1-G6 proved that the isolated compounds were pure and were not artifacts. Finally, RP-HPLC-ESI-MS-MS was used to identify substances G1-G6 in phytopharmaceutical drugs.

The key step in chlorophyll breakdown in higher plants. Cleavage of pheophorbide a macrocycle by a monooxygenase

Chlorophyll breakdown in green plants is a long-standing biological enigma. Recent work has shown that pheophorbide a (Pheide a) derived from chlorophyll (Chl) is converted oxygenolytically into a primary fluorescent catabolite (pFCC-1) via a red Chl catabolite (RCC) intermediate. RCC, the product of the ring cleavage reaction catalyzed by Pheide a oxygenase, which is suggested to be the key enzyme in Chl breakdown in green plants, is converted into pFCC-1 by a reductase. In the present study, an in vitro assay comprising 18O2 Pheide a oxygenase and RCC reductase yielded labeled pFCC-1. Fast atom bombardment-mass spectrometric analysis of the purified pFCC-1 product revealed that only one of the two oxygen atoms newly introduced into Pheide a in the course of the cleavage reaction is derived from molecular oxygen. Analysis of the fragment ions located the oxygen atom derived from molecular oxygen on the formyl group of pyrrole B. This finding demonstrates that the cleavage of Pheide a in vascular plants is catalyzed by a monooxygenase. Chlorophyll breakdown is therefore indicated to be mechanistically related in higher plants and in the green alga Chlorella protothecoides.