Open structural assignments

Its open structure involving a 13-atom orifice, not counting the bridging -COO-moieties, was assigned on the basis of NMR and IR data. The precursor compound 35 exhibits a reactive [5,6]-double bond, which is very susceptible to O2 addition. 

Glyeidol has been converted into 1 -ethoxy-2,3-propanediol (Eq. 561) by treatment with sodium ethoxide or with acidic ethanol.8 Similarly, methyl and isobutyl glycidyl ethers (Eq. 362) have been reported to undergo cleavage with methanol under various con-ditiom.ia6z 1812 The last substance named reacted poorly, however, and the structure assigned to fte fission product may be open to question. 

The complexes are colorless, sublimable, crystalline solids and can be stored in air for several weeks with negligible decomposition. In both series of compounds, the 1,2,4-isomers are thermally more stable than the 1,2,3-isomers owing to the greater charge separation in the former. The structural assignment (see Fig. 12) is once more based mainly on NMR spectroscopic data. It is suggested that the germanium atom in the compounds LXVIa,b is displaced toward the boron atoms on the open face of the n system. 

The reaction of 2-amino-4,5-dihydro-3-furancarboxylic esters (51) with amines appears interesting85. In contrast to the structure assigned earlier86-88, the reaction products have been later identified as 1,1-enediamines attached to a lactone moiety85. Thus, substrate 51 reacts with methylamine to give acyclic 1,1-enediamines 52 with an approximate E/Z ratio of 40 60. The reaction involves 4,5-dihydrofuran ring-opening and lactone-formation steps (Scheme 3). In the case of ethylenediamine and 1,3-diaminopropane, the reaction of 51 leads to the formation of cyclic 1,1-enediamine... 

The 80 K ion mobility spectrum, shown in the right panel of Fig. 8, exhibits two distinct features, which are readily assigned to the two families of closed and open structures [60]. This means that interconversion between the two families of structures is frozen out at 80 K, but is rapid at 300 K. Data taken between 110 and 190 K show that the two peaks present at low temperature melt into one at higher temperatures. Analysis analogous to the previous examples yields an activation barrier for the open-to-closed conversion of 1.6 kcal mol-1. The open-to-closed reaction turns on more rapidly than the reverse reaction, and the closed form is found to be 0.5 kcal mol-1 more stable than the open form [60]. 

Another series of interesting thiosugars was prepared by Schubert by the action of cysteine on the aldoses. By analogy with the structure assigned by this same author to the reaction product of cysteine with ordinary aldehydes, these new compounds may be formulated as the open chain forms ... 

Therefore, we have isolated the two products and have assessed their ability to act as substrates for two y-GH s isolated from chick pancreas and hog kidney. These two hydrolases differentially cleave the poly-y-glutamate chain at two distinct y-glutamyl peptide bonds (Scheme HI, open arrow (hog kidney) and filled arrow (chick pancreas)). The results of these enzyme-catalyzed hydrolyses provides strong evidence for the structures assigned to the reaction products as AMPteGlu-y Glu... 

In 1984, a yellow pigment was isolated from the petals of Carthamus tinctorius.13 The structure assigned to the isolate is shown in Figure 1.3.2 and contains an open-chain C-glycoside. 

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