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111.
Daniel Townsend Prof. Dr. Kenneth Shankland Dr. Alex Weymouth-Wilson Dr. Zofia Komsta Dr. Tim Evans Dr. Alexander J. A. Cobb 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(16):3504-3508
A highly enantioselective, organocatalytic, and scalable synthesis of a very unusual cis-decalin-cis-hydrindane tricyclic diterpenoid system has been achieved. Despite the prevalent pharmacological space that the related trans,trans and trans,cis-systems occupy, there have been no reports of an asymmetric synthesis of the cis,cis systems in the literature until now. We demonstrate the flexibility of our approach not only through access to a diverse range of products, all of which are attained in exceptionally high selectivities, but also by showing their easy conversion to the corresponding trans,cis-system and other derivatives. 相似文献
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In this paper we present a-posteriori KAM results for existence of d-dimensional isotropic invariant tori for n-DOF Hamiltonian systems with additional independent first integrals in involution. We carry out a covariant formulation that does not require the use of action-angle variables nor symplectic reduction techniques. The main advantage is that we overcome the curse of dimensionality avoiding the practical shortcomings produced by the use of reduced coordinates, which may cause difficulties and underperformance when quantifying the hypotheses of the KAM theorem in such reduced coordinates. The results include ordinary and (generalized) iso-energetic KAM theorems. The approach is suitable to perform numerical computations and computer assisted proofs. 相似文献
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Anaí Duarte Wilson Cunico Claudio M.P. Pereira Alex F.C. Flores Rogério A. Freitag Geonir M. Siqueira 《Ultrasonics sonochemistry》2010,17(2):281-283
An ultrasound-enhanced method has been developed for the synthesis of a variety of thioesters from benzoyl chlorides and 2-mercaptobenzoxa(thia)zoles. Applying this methodology, 14 compounds were synthesized in excellent yields. 相似文献
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Alex G. Harrison 《Journal of the American Society for Mass Spectrometry》2013,24(10):1555-1564
The fragmentation reactions of the MH+ ions as well as the b7, a7, and a7* ions derived therefrom have been studied in detail for the octapeptides MAAAAAAA, AAMAAAAA, AAAAMAAA, and AAAAAAMA. Ionization was by electrospray using a QqToF mass spectrometer, which allowed a study of the evolution of the fragmentation channels as a function of the collision energy. Not surprisingly, the product ion mass spectra for the b7 ions are independent of the original precursor sequence, indicating macrocyclization and reopening to the same mixture of protonated oxazolones prior to fragmentation. The results show that this sequence scrambling results in a distinct preference to place the Met residue in the C-terminal position of the protonated oxazolones. The a7 and a7* ions also produce product ion mass spectra independent of the original peptide sequence. The results for the a7 ions indicate that fragmentation occurs primarily from an amide structure analogous to that observed for a4 ions (Bythell et al. in J Am Chem Soc 132:14766–14779, 2010). Clearly, the rearrangement reaction they have proposed applies equally well to an ions as large as a7. The major fragmentation modes of the MH+ ions at low collision energies produce b7, b6, and b5 ions. As the collision energy is increased further fragmentation of these primary products produces, in part, non-direct sequence ions, which become prominent at lower m/z values, particularly for the peptides with the Met residue near the N-terminus. Figure
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