Polycyclic small molecules

Tan DS, Foley MA, Stockwell BR, Shair MD, Schreiber SL, Synthesis and preliminary evaluation of a library of polycyclic small molecules for use in chemical genetic assays, J. Am. Chem. Soc., 121 9073-9087, 1999. 

A number of combinatorial-based syntheses have been reported. Andrus et al. prepared a solution-phase indexed combinatorial library of nonnatural polyenes such as 291 for multidrug resistance reversal.298 This library was formed by modification of R and R. Ellman and co-workers reported a combinatorial library of synthetic receptors targeting vancomycin-resistant bacteria,209 and Paterson et al. prepared polyketide-type libraries by iterative asymmetric aldol reactions on solid support.2l0 Rieser et al. used combinatorial liquid-phase synthesis to prepare [1,4]-oxazepine-7-ones by the Baylis-Hillman reaction (see sec. 9.7.B).2H Schreiber and co-workers reported the synthesis and evaluation of a library of polycyclic small molecules for use in chemical genetic assays.2 2 Bauer et al. reported a library of N-substituted 2-pyrazoline compounds... 

FIGURE 11.86 Octahydrobenzisoxazole scaffold for the construction of library 190 of over 2 million compounds. (From Tan, D.S. et al.. Stereoselective synthesis of over two million compounds having structural features both reminiscent of natural products and compatible with miniaturized cell-based assays, J. Am. Chem. Soc., 120, 8565, 1998 Tan, D.S., Synthesis and preliminary evaluation of a library of polycyclic small molecules for the use in chemical genetic assays, J. Am. Chem. Soc., 121, 9073, 1999.)... 

Unbumed Hydrocarbons Various unburned hydrocarbon species may be emitted from hydrocarbon flames. In general, there are two classes of unburned hydrocarbons (1) small molecules that are the intermediate products of combustion (for example, formaldehyde) and (2) larger molecules that are formed by pyro-synthesis in hot, fuel-rich zones within flames, e.g., benzene, toluene, xylene, and various polycyclic aromatic hydrocarbons (PAHs). Many of these species are listed as Hazardous Air Pollutants (HAPs) in Title III of the Clean Air Act Amendment of 1990 and are therefore of particular concern. In a well-adjusted combustion system, emission or HAPs is extremely low (typically, parts per trillion to parts per billion). However, emission of certain HAPs may be of concern in poorly designed or maladjusted systems. 

With the help of the steepest descent process usually final absolute d E/3 x(--values of about 0.1 kcal mole-1 A-1 may be reached. By means of the Newton-Raphson procedure these values may in most cases easily be lowered to about 10-6 kcal mole-1 A-1. Only with a few rigid polycyclic systems and with some small molecules were we able to ap-... 

Figure 7.1 Some small polycyclic hydrocarbon molecules here C Hm means n vertices (carbon atoms) including m 2-valent ones, where a hydrogen atom can be attached (double bonds are omitted for simplicity) ...

One impediment to straightforward comparison is the lack of solid-phase enthalpies of formation for most low molecular weight molecules. Examination of the few examples for which there are both solid- and liquid-phase values shows, however, that the liquid- and solid-phase enthalpies of reaction do not vary too much, at least within the uncertainties of the steroid combustion measurements. We are additionally hampered by not having available enthalpies of formation for those small molecules which most resemble the steroid substructure. The prototype small molecules required for the analysis are primarily those of substituted five- or six-membered carbocyclic rings. Although the functional groups on the available prototypes and the steroids are identical, stereochemical aspects (such as axial vs. equatorial substituent positions) and their consequent interactions are different due to the differences in conformational flexibility of the monocyclic and polycyclic systems. The prototype molecules and their liquid-phase enthalpies of formation are listed in Table 3. 

Soot forms in a flame as the result of a chain of events starting with the oxidation and/or pyrolysis of the fuel into small molecules. Acetylene, C2H2, and polycyclic aromatic hydrocarbons (PAHs) are considered the main molecular intermediates for soot formation and growth (McKinnon and Howard 1990). The growth of soot particles involves first the formation of soot nuclei and then their rapid growth due to surface reactions (Harris and Weiner 1983a,b). 

The DNA molecule is the primary target of many antitumour agents. Small molecules, which bind to DNA by intercalation, require polycyclic systems in their structure for efficient binding. Because of the symmetrical arrangement of the helical double strand, symmetry is found in the structure of DNA ligands. Polycyclic systems bearing symmetrical polyamine side chains, such as mitoxantrone ... 

DOS aims to provide structurally complex and diverse small molecules efficiently for chemical genetic screens thus, in a pioneering study, Schreiber and coworkers synthesized a polycyclic library that mimics the complexity of the biologically active molecules. Chemical genetic assays identified compounds that activate the TGF-beta responsive reporter gene (Tan et al., 1999) (Figure 1.6). 

---