Cyclic substructures

A cap (substituent or side chain) is an acyclic substructure with one attachment connecting to other structure building blocks a linker is an acyclic substructure with more than one attachment connecting to other stmcture building blocks building blocks are functional groups and core structures and a com is a cyclic substructure without linker or cap. 

Dimethyl allene-l,3-dicarboxylate 476 can react with a variety of nucleophiles with an N=C-NH2 substructure to afford monocyclic or bicyclic compounds 501. In this reaction the iminyl nitrogen first attacks the center carbon atom of the allene moiety to afford 3-amino-4-(methoxycarbonyl)-2-butenoate, in which the other nitrogen atom and the conjugated carboxylate undergo an aminolysis reaction to afford the cyclic product [226],... 

New methods for the synthesis of 2,4-disubstitued oxazoles are summarized in a recent review. 2-Alkyl-1,3-oxazoles bearing alkyl, aryl, or acyl substitution at C4 are common substructures in natural products. Examples include macrolides such as rhizoxin (4), hennoxazole A (5), and phorboxazole A (6), ° as well as many cyclic peptides that incorporate an oxazole subunit presumably derived from serine. ... 

Clearly, for fullerenes with a lower symmetry, local substructures, such as the cyclic phenylene belt of C7Q, can also largely determine the magnetic behavior. 

The imidazopyrazine substructure occurs in luciferins from a wide range of organisms living in the sea and in ostracod crustaceans, e.g. Cypridina. The chemistry of the luminescent effect in these systems involves reaction with oxygen to form a stable cyclic dioxetanone, similar to the hrefly luciferin as indicated in (3.108). 

A second example is that involving the use of a glucopyranoside nonpeptide template by Hirschmann and coworkers [41, 46] for systematic functionalization to create novel peptidomimetics for the somatostain (SRIF) and substance-P (NKj) receptors. As illustrated in Figure 10, the cyclic hexapeptide SRIF agonist provided a macrocyclic lead stmcture that was transformed to a glucopyranoside template designed to substitute for a postulated 3 turn about the Tyr-D-Trp-Lys-Thr substructure of the parent peptide ligand. The prototype... 

Carbon-13 shift of common non-aromatic heterocycles with endo- and exocyclic double bonds are reviewed in Table 4.66 [416-432], - Deshieldings of / -carbons induced by carbonyl groups in heterocyclic a, /1-enones due to (—)-M electron withdrawal (e.g. 2-pyrones, coumarins) and shieldings of [ carbons in cyclic enol ethers arising from (+ )-M electron release (e.g. 2,3-dihydrofuran and oxepine derivatives in Table 4.66) fully correspond to the effects described for the open-chain analogs. Outstandingly large shift values are observed for the lithiated carbon in cyclic a-lithium enol ethers (Table 4.66). In terms of its a and / carbon-13 shifts, 2,7-dimethyloxepine is also a typical enol ether [420], Further, 2,6-dimethyl-4-pyrone [421] and flavone [422] display similiar shift values for the a, /1-enone substructure. 

Solov ev, V.P Vamek, A. Anti-HIV activity of HEPT, TIBO, and cyclic urea derivatives Structure-property studies, focused combinatorial library generation, and hits selection using substructural molecular fragments method. J. Chem. Inf. Comp. Sci. 2003,43 (5), 1703-1719. 

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