The d in the structural label indicates that the compound bears a deuterium substituent, Z = D. For the sake of clarity; the absolute configurations of these labeled species have been assigned without any consideration of the deuterium atom. Therefore, the structural labels for the deuterated and the corresponding protiated compounds differ only in the presence or absence of d following the number for that structure. Although the compounds bearing deuterium are mixtures of diastereomers, no evidence has been observed which indicates a diastereomeric composition which is not equal to 1:1. (20) J.

Piper betle Linn. is a traditional plant associated with the Asian and southeast Asian cultures. Its use is also recorded in folk medicines in these regions. Several of its medicinal properties have recently been proven. Phytochemical analysis showed the presence of mainly terpenes and phenols in betel leaves. These constituents vary in the different cultivars of Piper betle. In this paper we have attempted to profile eight locally available betel cultivars using the recently developed mass spectral ionization technique of direct analysis in real time (DART). Principal component analysis has also been employed to analyze the DART MS data of these betel cultivars. The results show that the cultivars of Piper betle could be differentiated using DART MS data.

Tandem mass spectra of ammonium adducts of monosaccharides gave characteristic fragmentation patterns involving elimination of NH3/H2O followed by multiple eliminations of H2O and cross ring cleavages. Tandem mass spectra were examined over a range of collision energies (1-20 eV) on a triple-quadrupole mass spectrometer. The breakdown behavior of the ammonium adducts revealed patterns that could differentiate diastereomers of monosaccharides.

Multiple lithium exchange is observed during electrospray ionization of alpha-, beta- and gamma-cyclodextrins from aqueous methanolic solution containing LiOH. Apart from [M + Li](+) and [M + nLi - (n - 1)H](+) ions, abundant multiply lithiated doubly charged ions corresponding to [M + nLi - (n - 2)H](2+) ions were observed. At least six lithium exchanges in alpha-cyclodextrin, seven in beta-cyclodextrin and eight in gamma-cyclodextrin were noted. The propensity of multiply lithiated doubly charged ions is much less in the open-ended maltoheptaose. It appears that during droplet or cluster formation and subsequent desolvation, LiOH trapped in the cavity of cyclodextrin reacts to form multiply lithiated ions. The singly charged [M + Li](+) and doubly charged [M + 2Li](2+) ions fragment by glycosidic cleavages, giving B series of ions, whereas the multiply lithiated ions fragment by cross ring cleavages ((2, 4)A or (O, 2)X) followed by glycosidic cleavage. From the tandem mass spectra, it appears that a maximum of two lithium exchanges occur in one sugar unit in these cyclodextrins.

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endo-cis-(2S,3R)-Bicyclo[2.2.1]hept-5-en (norbornene) dicarbonyl unit with a built-in U-architecture has been demonstrated to be an excellent reverse-turn molecular scaffold. A large variety of endo-cis-(2S,3R)-norborneno bispeptides containing almost all of the coded amino acids were synthesized and examined for conformational preferences by 1H NMR, FT-IR, CD, and X-ray crystallographic studies. While FT-IR and 1H NMR variable-temperature studies ruled out the presence of any significant amount of intramolecular hydrogen bonding in simple bispeptides (3a − h) (except in Aib bispeptide), the CD studies were clearly in favor of a β-turn type structure. Single-crystal X-ray studies on Aib, Val and Leu containing norborneno bispeptides (3b−d) provided convincing proof for the presence of reverse-turn conformation. While the interstrand Cα−Cα‘ distances (5.2−5.7 Å) were well within the range of those for β-turn structures, no interstrand intramolecular hydrogen bonding was seen in Val and Leu bispeptides; the Aib bispeptide forms a seven-membered hydrogen-bonded ring, thus, showing that the norbornene (2S,3R)-dicarbonyl template assembles peptide chains in reverse-turn conformation by virtue of its built-in U-shaped architecture at these positions, and hydrogen bonding may not be necessary to stabilize the turn structure. The endo-cis-(2S,3R) orientation of bispeptide chains is essential for turn structure as shown by the crystal structure of trans-(2R, 3R) and trans-(2S,3S) derivative of Val bispeptide wherein the two peptide chains move away from each other with the Cα−Cα‘ distance increasing to 7.1−8.2 Å. The norbornene 5,6-double bond was hydrogenated to 5,6-dihydro derivative which showed almost the same CD spectrum as its olefinic analogue. Oxidative cleavage [Ru (VIII)] of the 5,6-double bond in norborneno bispeptides, as demonstrated with Leu bispeptide, afforded novel cyclopentanoid peptide analogues. The promise of norbornene unit as a template for nucleating the formation of two-stranded parallel β-sheets with minimum structural complexity is shown by the preparation of higher members of norborneno bispeptides with the general structure NBE(Pep)2 [NBE = endo-cis-(2S,3R)-bicyclo[2.2.1]hept-5-en (norbornene) dicarbonyl unit; Pep = peptide strand with two, three, or four (same or different) amino acid residues]. In 1H NMR, the high 3 J HN α values (7.0−9.3 Hz) observed for the amide protons (Table ) coupled with the presence of medium to strong intrastrand sequential ROE connectivities d α N( i , i +1) spanning the entire three- or four-residue sequence in the peptide strands of 9a − e and 10 and the exhibition of relatively low-temperature coefficients (dδ/dT = − 0.2 to −3.4 ppb/K) for amide protons in DMSO-d 6 solvent (Table ) clearly suggested that hydrogen-bonded β-sheet conformers dominate the population. FT-IR and CD studies provided further support for parallel β-sheet structures. A particularly unique feature of the norborneno bispeptides is their strong tendency to self-assemble in the solid sta...

LC-ESI-MS analysis was carried out for taxoid profiling of partially purified methanol extracts of the stem bark of Taxus wallichiana growing in different regions of the Himalayas (Kashmir, Himachal Pradesh, UP hills, Sikkim and Arunachal Pradesh). Cone voltage fragmentation of the protonated, ammonium or sodium cationized molecular species resulted in diagnostic fragment ions. Thus, information about the number and nature of substituents and the taxane skeleton (whether it is normal or rearranged) was readily available from the LC-ESI-MS spectra. The rearranged 11(15-->1)-abeo-taxanes showed a characteristic elimination of the hydroxyisopropyl along with an acetoxy group. The identification of the taxoids was achieved by comparison of the ESI mass spectra with those of the authentic taxoids available to us or by interpreting the ESI mass spectra. The results were also corroborated by MS/MS analysis of the partially purified extract injected directly into the ESI source. Paclitaxel, its analogues and their xylosides are present in samples from all the regions. An interesting observation is the detection of a large number of basic taxoids having nitrogen-containing side chains.