Structures Systems Fragment-Based

The program system COBRA [118, 119] can be regarded as a rule- and data-based approach, but also applies the principles of fragment-based (or template-based) methods extensively (for a detailed description sec Chapter 11, Sections 7.1 and 7.2 in the Handbook). COBRA uses a library of predefined, optimized 3D molecular fragments which have been derived from crystal structures and foi ce-field calculations. Each fi agment contains some additional information on... 

Complexes may also be constructed of a fusion of open fragments. For 7 this can lead to the well-known cubane class of complexes 15 (Table V). The cubane core is a structure found naturally in biological systems having E = S and metal fragments based upon Fe and/or Mo. Organometallic... 

Access to all this information is provided by the Index Chemicus Registry System (ICRS), which contains records of new compounds and associated data on magnetic tape (6). Structures are described by the Wiswesser Line Notation (7), a system for describing chemical formulas in terms of a linear groups of symbols. A recent development is the ICRS Substructure Index (G5), which enables manual searches to be made for new chemical information, and is based on the occurrence of fragments of structures, the most common of which are illustrated as conventional structural diagrams. 

Nilakantan R, Nunn DS, Greenblatt L, Walker G, Haraki K, et al. A family of ring system-based structural fragments for use in structure-activity studies Database mining and recursive partitioning. J Chem Inf Model 2006 46(3) 1069-77. 

The elimination of water from the molecular ion of 106 is of diagnostic value only for simple systems. The mass spectra of compounds containing a larger number of methoxy substituents show (M—H20)+ fragments even for systems with nonad-jacent substituents. For the radical cations formed by loss of water from 106, the structure of benzofurane, 107, was proposed based on the metastable ion characteristics1 1S ... 

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