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1.
A short and efficient synthesis of 2'-O-methoxyethylguanosine (8) is described. Central to this strategy is the development of a novel silicon-based protecting group (MDPSCl(2), 2) used to protect the 3',5'-hydroxyl groups of the ribose. Silylation of guanosine with 2 proceeded with excellent regioselectivity and in 79% yield. Alkylation of the 2'-hydroxyl group of 6 proceeded with methoxyethyl bromide and NaHMDS and afforded compound 7 in 85% yield, without any noticeable cleavage of the silyl protecting group and without the need to protect the guanine base moiety. Finally, deprotection of 7 was achieved using TBAF and produced 8 in 97% yield. 相似文献
2.
Manvendra B. Shambhu Michael C. Theodorakis George A. Digenis 《Journal of polymer science. Part A, Polymer chemistry》1977,15(3):525-531
Three polyamine ligands, ethylenediamine (EDA), diethylenetriamine (DTA), and triethylenetetramine (TETA), were bound to three chloromethylated “popcorn” polystyrene resins (16, 50, and 100% phenyl ring substitution) with the use of pyridine as the reaction medium. The rate of chloride displacement decreased with increasing molecular weight of the amine and higher degree of resin chloromethylation, while the extent of multiple attachments to the polymer matrix increased. The additional crosslinking, a result of multiple attachments, caused the polyamine resins to swell to a lesser extent in pyridine and water. The ability of the insoluble polyamine–polystyrene resins to chelate Cu2+ ions from dilute solutions (200 ppm) was determined at pH 5. With EDA resins the capacity for Cu2+ increased with increasing amount of the bound polyamine, with DTA it remained unchanged, while with TETA it was found to decrease. 相似文献
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[reaction: see text] Two different routes to the tricyclic core of Garcinia-derived natural products are described. The first approach is based on a tandem Claisen/Diels-Alder rearrangement and delivers the desired lactone 14. The second approach, employing a Wessely oxidation/Diels-Alder protocol, leads to the same caged heterocycle, albeit with modified constitution. 相似文献
5.
[reaction: see text] A stereoselective synthesis of (-)-ilimaquinone (4) is presented. The synthetic strategy is based on a novel radical decarboxylation and quinone addition methodology that produces quinone 7 from reaction of thiohydroxamic acid derivative 8 with benzoquinone (9). Final functionalization of 7 to ilimaquinone (4) is achieved by exploring the electronic effects of the residual thiopyridyl group. 相似文献
6.
Dr. Lynnie Trzoss Dr. Jing Xu Michelle H. Lacoske Prof. Dr. William C. Mobley Prof. Dr. Emmanuel A. Theodorakis 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(20):6398-6408
Majucin‐type sesquiterpenes from Illicium sp., such as jiadifenolide ( 2 ), jiadifenin ( 3 ), and (1R,10S)‐2‐oxo‐3,4‐dehydroxyneomajucin ( 4 , ODNM), possess a complex caged chemical architecture and remarkable neurotrophic activities. As such, they represent attractive small‐molecule leads against various neurodegenerative diseases. We present an efficient, enantioselective, and unified synthesis of 2 , 3 , and 4 and designed analogues that diverge from tetracyclic key intermediate 7 . The synthesis of 7 is highlighted by the use of an enantioselective Robinson annulation reaction (construction of the AB rings), a Pd‐mediated carbomethoxylation reaction (construction of the C ring), and a one‐pot oxidative reaction cascade (construction of the D ring). Evaluation of the neurotrophic activity of these compounds led to the identification of several highly potent small molecules that significantly enhanced the activity of nerve growth factor (NGF) in PC‐12 cells. Moreover, efforts to define the common pharmacophoric motif suggest that substitution at the C‐10 center significantly affects bioactivity, while the hemiketal moiety of 2 and 3 and the C‐1 substitution might not be critical to the neurotrophic activity. 相似文献
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Two-component bottle-brush polymers, where flexible side chains containing N = 20, 35 and 50 effective monomers are grafted alternatingly to a rigid backbone, are studied by Molecular Dynamics simulations,
varying the grafting density s \sigma and the solvent quality. Whereas for poor solvents and large enough s \sigma the molecular brush is a cylindrical object with monomers of different type occupying locally the two different halves of
the cylinder, for intermediate values of s \sigma an axially inhomogeneous structure of “pearl-necklace” type is formed, where microphase separation between monomers of different
type within a cluster takes place. These “pearls” have a strongly non-spherical ellipsoidal shape, due to the fact that several
side chains cluster together in one “pearl”. We discuss the resulting structures in detail and we present a comparison with
the single-component bottle-brush case. 相似文献
9.
P. E. Theodorakis N. G. Fytas 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,81(2):245-251
We implement a two-stage approach of the Wang-Landau algorithm to investigate the critical properties of the 3D Ising
model with quenched bond randomness. In particular, we consider the case where disorder couples to the nearest-neighbor
ferromagnetic interaction, in terms of a bimodal distribution of strong versus weak bonds. Our simulations are carried out
for
large ensembles of disorder realizations and lattices with linear sizes L in the range L=8-64L=8{-}64. We apply well-established
finite-size scaling techniques and concepts from the scaling theory of disordered systems to describe the nature of the phase
transition of the disordered model, departing gradually from the fixed point of the pure system. Our analysis (based on the
determination of the critical exponents) shows that the 3D random-bond Ising model belongs to the same universality class
with the site- and bond-dilution models, providing a single
universality class for the 3D Ising model with these three types of quenched uncorrelated disorder. 相似文献
10.
An enantioselective strategy for the synthesis of tetracyclic motif 5, representing the northern fragment of norzoanthamine, is presented. Key to the strategy is the use of two asymmetric Robinson annulation reactions that produce the tricyclic ABC ring system with excellent stereoselectivity. Further functionalization at the periphery of the C ring produces compound 5 containing six contiguous stereocenters of the natural product. 相似文献