Gross structure

Reactions can be considered as composite systems containing reactant and product molecules, as well as reaction sites. The similarity of chemical structures is defined by generalized reaction types and by gross structural features. The similarity of reactions can be defined by physicochemical parameters of the atoms and bonds at the reaction site. These definitions provide criteria for searching reaction databases [23],... 

Recognition of functional groups or gross structural features. 

In the case of phenazine, substitution in the hetero ring is clearly not possible without complete disruption of the aromatic character of the molecule. Like pyrazine and quinoxa-line, phenazine is very resistant towards the usual electrophilic reagents employed in aromatic substitution reactions and substituted phenazines are generally prepared by a modification of one of the synthetic routes employed in their construction from monocyclic precursors. However, a limited range of substitution reactions has been reported. Thus, phenazine has been chlorinated in acid solution with molecular chlorine to yield the 1-chloro, 1,4-dichloro, 1,4,6-trichloro and 1,4,6,9-tetrachloro derivatives, whose gross structures have been proven by independent synthesis (53G327). 

In retrospect it is easy to see that such structural irregularity is actually required for proteins to fulfill their diverse functions. Information storage and transfer from DNA is essentially linear, and DNA molecules of very different information content can therefore have essentially the same gross structure. In contrast, proteins must recognize many thousands of different molecules in the cell by detailed three-dimensional interactions, which... 

The 434 Cro molecule contains 71 amino acid residues that show 48% sequence identity to the 69 residues that form the N-terminal DNA-binding domain of 434 repressor. It is not surprising, therefore, that their three-dimensional structures are very similar (Figure 8.11). The main difference lies in two extra amino acids at the N-terminus of the Cro molecule. These are not involved in the function of Cro. By choosing the 434 Cro and repressor molecules for his studies, Harrison eliminated the possibility that any gross structural difference of these two molecules can account for their different DNA-binding properties. 

The ultraviolet spectra of many substituted aminopyridines were reported in 1959 with rather vague reference to their tautomerism however, the gross structure assigned to some of the sulfonamido compounds has been criticized. ... 

In 1952, it was reported that a constituent of excretions from female American cockroaches of the species Periplaneta ameri-cana is an extraordinarily potent sex pheromone.1 Early attempts to isolate and characterize the active compounds were hampered because individual cockroaches store only minute amounts of the pheromone ( 1 pg), and a full 25 years elapsed before Persoons et al. reported the isolation of two extremely active compounds, periplanones A and B.2 The latter substance is present in larger relative measure and its germacranoid structure (1, without stereochemistry) was tentatively assigned on the basis of spectroscopic data. Thus, in 1976, the constitution of periplanone B was known but there remained a stereochemical problem of a rather serious nature. Roughly three years intervened between the report of the gross structure of periplanone B and the first total synthesis of this substance by W. C. Still at Columbia.3... 

On a gross, structural basis, it would appear that removal of the a-D-NeuAc groups does not substantially perturb the structure about the N-terminus. However, deglycosylation of almost the entire molecule seems to have a profound effect this structural effect about the N-terminus appears to be heavily associated with glycophorin (see Fig. 6 and later ). 

Axisonitrile-1 (1) and axisothiocyanate-1 (2) were the first pair of NC/NCS compounds isolated from Axinella cannabina, see Introduction [1]. That both compounds possessed a new skeleton was evident, when 1 was reduced (Li/EtNH2) to axane (6). Other transformations involving the exocyclic methylene which survived selective reduction (Na/NH3) of 1, coupled with evaluation of the lHNMR data, supported its gross structure. Confirmation of 2 was secured when 1 was heated with sulfur and the resultant purified product found to be identical to the natural product. 

Shortly after amphilectanes 96 and 97 were reported, other metabolites from Amphimedon were isolated, with the majority of their structures supported by the corresponding spectral and X-ray data. Although the gross structures of the series, 98-100, are regio isomers with respect to one of the isocyano functions, they also exhibit minor differences in the C4 moiety attached to C-l. X-ray determination of 98 led to assignment of its relative stereochemistry, thereby securing assignments for 99 and 100 by comparison of spectroscopic data [61]. 

The synthesis of catalytic photocathodes for H2 evolution provides evidence that deliberate surface modification can significantly improve the overall efficiency. However, the synthesis of rugged, very active catalytic surfaces remains a challenge. The results so far establish that it is possible, by rational means, to synthesize a desired photosensitive interface and to prove the gross structure. Continued improvements in photoelectrochemical H2 evolution efficiently can be expected, while new surface catalysts are needed for N2 and CO2 reduction processes. 

The epoxide selectivity did not depend noticeably on the gross structural features of the catalyst. For instance, the selectivity in the epoxidation of 4 is about 85% on all solids (Table XIII). 

The only reasonable explanation for these data is represented by gross structure 309. This could be derived from a pseudotabersonine-subtype precursor by a sequence of electrophilic hydroxylation at C-16, followed by acid-catalyzed... 

The gross structure of 73 was determined by a combination of spectroscopic and chemical means (112) stereochemistry was proved by single-crystal X-ray diffraction (113). Much later, 73 was also found in C. guianensis from Brazil (114). It was characterized by PMR and CMR data as well as by X-ray analysis. Gerrardine showed activity against Salmonella spp. (115), Candida albicans T.A., Escherichia coli, and Klebsiella pneumoniae D.T. (114). 

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