Subject selective coupling

Most interestingly, allylsilanes, stannanes, and silyl enolethers function as nucleophiles in the reactions described here and are subject to the same stereochemical preferences as alcohols [148, 149]. Thus, unselective reactions are observed with a per-O-benzyl mannopyranosyl donor, p-selective couplings are seen with a 4,6-0-benzylidene protected mannopyranosyl donor, and ot-selective reactions with the corresponding glucopyranosyl donor (Scheme 46). 

As another subset of our approach, we chose a few known nonflat cores and enumerated them with derived fragments. These cores were subjectively selected from known drugs and literature. The list used below for this exercise is not exclusive and can be expanded based on requirements [18,19]. The nonflat cores are depicted in blue. Typically, they have more than one point of diversification. For ease of handling, we fixed one diversification point with a commonly found hydrophobic (hp) group (hp = fluorophenyl, cylopropyl, etc.). The other diversification point was used for coupling with the aforementioned daughters. 

In common with all multidimensional separations, two-dimensional GC has a requirement that target analytes are subjected to two or more mutually independent separation steps and that the components remain separated until completion of the overall procedure. Essentially, the effluent from a primary column is reanalysed by a second column of differing stationary phase selectivity. Since often enhancing the peak capacity of the analytical system is the main goal of the coupling, it is the relationship between the peak capacities of the individual dimensions that is crucial. Giddings (2) outlined the concepts of peak capacity product and it is this function that results in such powerful two-dimensional GC separations. 

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