Butyryl groups

The net result of this biosynthetic cycle is the synthesis of a four-carbon unit, a butyryl group, from two smaller building blocks. In the next cycle of the process, this butyryl-ACP condenses with another malonyl-ACP to make a... 

Steps 6-8 of Figure 29.5 Reduction and Dehydration The ketone carbonyl group in acetoacetyl ACP is next reduced to the alcohol /S-hydroxybutyry] ACP by yS-keto thioester reductase and NADPH, a reducing coenzyme closely related to NADH. R Stereochemistry results at the newly formed chirality center in the /3-hydroxy thioester product. (Note that the systematic name of a butyryl group is biitanoyl.)... 

The net effect of the eight steps in the fattv-acid biosynthesis pathway is to take two 2-carbon acetyl groups and combine them into a 4-carbon butyryl group. Further condensation of the butyryl group with another malonyl AGP yields a 6-carbon unit, and still further repetitions of the pathway add two more carbon atoms to the chain each time until the 16-carbon palmitoyl ACP is reached. 

It is noteworthy that acetylated wood meals prepared by the TFAA method melted clearly at 320°C under a pressure of 0.29 MPa [4,5]. Other methods of acetylation resulted in products that did not undergo complete flow. However, thermal properties of the acetylated wood were enhanced by mixed esterification with other acyl groups. That is, esterified woods containing either propio-nyl or butyryl groups in addition to acetyl revealed meltable properties [4,5]. A film prepared from the acetylated-butyrylated wood meal has a tensile strength of 41.0 MPa and an elongation of 12.5% [41. 

Figure 10.8. Effect of cAMP on insulin secretion in pancreatic islet cells, a Stracture of the membrane-permeant analog dibutyryl-cAMP. The two butyryl groups and the acetyl group will be cleaved intracellularly, releasing cAMP. b Glucose-de-pendent insulin secretion in the presence or absence of dibutyryl-cAMP. cAMP amplifies glucose-dependent secretion, c Suppression of cAMP-mediated stimulation of insulin secretion by the a2-agonist clonidine. (Data from Life Sci. 32 191-95,1983.)...

The mixed organic esters of cellulose most prominent commercially are the acetate propionate and acetate butyrate. The cellulose in these products is esterihed partly by acetyl and partly by propionyl or butyryl groups. The products are uniform compounds, giving clear, homogeneous solutions and plastic compositions. 

The solubility restrictions that apply to the manufacture of the mixed esters are the same as those for the cellulose acetate, in that no soluble products are obtained by partial esterification. Hydrolysis of the esters in acid solution, however, yields uniform products showing gradually changing physical properties with increasing free hydroxyl content. The exact ratio of hydrolysis of acetyl to hydrolysis of propionyl or butyryl groups depends upon the composition of the hydrolysis solution. Thus, a cellulose acetate propionate hydrolyzed in acetic acid solution will retain a higher proportion of acetyl groups than would the same cellulose ester hydrolyzed in propionic acid. 

Fatty acids have predominantly even numbers of carbon atoms because they are effectively formed from acetyl (C2) units, which are derived from glucose in the presence of various enzymes, coenzymes and carrier proteins. An overall scheme for saturated fatty acid biosynthesis is presented in Fig. 2.13, in which it can be seen that the first step is the formation of acetyl coenzyme A (often abbreviated to acetyl-CoA). One molecule ofacetyl-CoA undergoes addition of CO, to form malonyl-CoA, while the acetyl group on another molecule is transferred to an enzyme (fatty acid synthase). The malonyl unit (C3) is added to the enzyme-bound acetyl unit, which produces a butyryl group following loss of C02, dehydration and reduction. Six further steps of combined malonyl addition, decarboxylation, dehydration and reduction occur to yield palmitate (C16). Higher acids are built from palmitate in a similar... 

Figure 29 Protected ManNAc analogs with C-1 or C-6 free hydroxyls (R = acetyl or butyryl groups). A free hydroxyl at the C-1 position has little effect on metabolic flux but negatively impacts cell viability. A free hydroxyl at the C-6 position improves metabolic flux and increases cell viability.

Figure 31 Structures of immunogenic ganglioside analogs, (a) Structure of GD3Bu-KLH (butyryl groups in red, KLH in blue), (b) Structure of GM3PAc-KLH (PAc in red, KLH in blue).

Cellulose butyrate contains the bulkier butyryl group these esters are more compatible and soluble than acetates, but are too soft for most coating applications. Cellulose esterified with blends of alkyl groups can provide many intermediate properties needed in coatings. Selection of the appropriate cellulose acetate butyrate [9004-36-8] (CAB) and cellulose acetate propionate [9004-39-f] (CAP) content must be based on specific application requirements. 

Properties. The large size and low polarity of the butyryl groups separate the cellulose chains and lowers the attraction between them. As butyryl content increases, properties are affected as follows ... 

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