Analogous Structures Identification

The tetraborane B4H2R4 (R = rBu) was found to react with 2-butyne to give the 1,5-dicarba-c/oso-pentaborane Me2C2B3R3 in 63 % yield [Eq. (8)]. The hypothetic second product (RBH2)2 is certainly not stable under the reaction conditions (160 °C, 6 bar, excess of butyne).8 The structural identification of the carbaborane by the NMR data followed well known data of analogous carbaboranes, e.g. Me2C2B3Et3.u... 

Reagent A has been used with aldehydes to prepare crystalline imidazolidine derivatives, such as B, for the purpose of their isolation and structural identification. Write a mechanism for the formation of B. [Hint Notice that the product is a nitrogen analog of an acetal. Develop a mechanism analogous to that for acetal formation (Section 17-7), using the two amino groups in the starting diamine in place of two alcohol molecules.]... 

An examination of the mass spectra of these isomeric compounds and of their D20-exchanged analogs leads to the conclusions that the spectra can be interpreted in terms of the structures 4-6 and that structural differences lead to extensive differences in fragmentation. These mass spectra now can be used for identification purposes and as models to aid in the interpretation of the mass spectra of similar compounds, possibly of unknown structure. 

After identification of A9-THC as the major active compound in Cannabis and its structural elucidation by Mechoulam and Gaoni in 1964 [66], a lot of work was invested in chemical synthesis of this substance. Analogous to the biosynthesis of cannabinoids, the central step in most of the A9-THC syntheses routes is the reaction of a terpene with a resorcin derivate (e.g., olivetol). Many different compounds were employed as terpenoid compounds, for example citral [67], verbenol [68], or chrysanthenol [69]. The employment of optically pure precursors is inevitable to get the desired (-)-trans-A9-THC. 

K. Mizutani, T. Electronic and structural requirements for metabolic activation of butylated hydroxytoluene analogs to their quinone methides, intermediates responsible for lung toxicity in mice. Biol. Pharm. Bull. 1997, 20, 571-573. (c) McCracken, P. G. Bolton, J. L. Thatcher, G. R. J. Covalent modification of proteins and peptides by the quinone methide from 2-rm-butyl-4,6-dimethylphenol selectivity and reactivity with respect to competitive hydration. J. Org. Chem. 1997, 62, 1820-1825. (d) Reed, M. Thompson, D. C. Immunochemical visualization and identification of rat liver proteins adducted by 2,6-di- m-butyl-4-methylphenol (BHT). Chem. Res. Toxicol. 1997, 10, 1109-1117. (e) Lewis, M. A. Yoerg, D. G. Bolton, J. L. Thompson, J. Alkylation of 2 -deoxynucleosides and DNA by quinone methides derived from 2,6-di- m-butyl-4-methylphenol. Chem. Res. Toxicol. 1996, 9, 1368-1374. 

Confirmation that the polymerizations proceed via metallacyclic intermediates was obtained by studying the ROMP of functionalized 7-oxanorbornadienes. These polymerize slower than their norbornene analogs, allowing NMR identification of the metallacyclobutane resonances and subsequent monitoring of ring opening to the first insertion product. In addition, the X-ray crystallographic structure of complex (212) has been reported.533... 

To correctly address the problem of identification of target-specific privileged motifs, one should take into account the phenomenon of bioisosterism [26]. Thus, several different bioisosteric structures can constitute only one distinct privileged structural motif. In order to include all possible bioisosteric analogs into one cluster, we use a special algorithm of ChemoSoft based on a collection of rules for bioisosteric conversions described in literature. AH bioisosteric analogs are considered similar with similarity coefficient 1 if they have identical substituents around the central bioisosterically transformed fragment. 

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