Cholic acid conformation

The bile acids are produced in the liver by the metabolism of cholesterol. They are di- and trihydroxylated steroids with 24 C atoms. The structure of cholic acid was seen earlier (Sec. 6.6). Deoxycholic acid and chenodeoxycholic acid are two other bile acids. In the bile acids, all the hydroxyl groups have an a orientation, while the two methyl groups are /3. Thus, one side of the molecule is more polar than the other. However, the molecules are not planar but bent because of the cis conformation of the A and B rings. 

Esters, Ethers, and Related Derivatives of Alcohols.— The long-recognized differences in reactivity of the 3a-, 7a-, and 12a-hydroxy-groups in cholic acid to acetylation (3a > 7a > 12a) have been attributed to conformational and steric effects [3a-equatorial 7a- and 12a-axial, and seemingly differentiated by greater steric hindrance at C(12), due to the side-chain]. A new investigation, however, shows that the reactivities of the monohydroxycholanic acids are in ratio 3a 7a 12a 97 1.0 1.5. ° A novel radioisotope method was used for... 

With this information in hand, it seemed reasonable to attempt to use force field methods to model the transition states of more complex, chiral systems. To that end, transition state.s for the delivery of hydrogen atom from stannanes 69 71 derived from cholic acid to the 2.2,.3-trimethy 1-3-pentyl radical 72 (which was chosen as the prototypical prochiral alkyl radical) were modeled in a similar manner to that published for intramolecular free-radical addition reactions (Beckwith-Schicsscr model) and that for intramolecular homolytic substitution at selenium [32]. The array of reacting centers in each transition state 73 75 was fixed at the geometry of the transition state determined by ah initio (MP2/DZP) molecular orbital calculations for the attack of methyl radical at trimethyltin hydride (viz. rsn-n = 1 Si A rc-H = i -69 A 6 sn-H-C = 180°) [33]. The remainder of each structure 73-75 was optimized using molecular mechanics (MM2) in the usual way. In all, three transition state conformations were considered for each mode of attack (re or ) in structures 73-75 (Scheme 14). In general, the force field method described overestimates experimentally determined enantioseleclivities (Scheme 15), and the development of a flexible model is now being considered [33]. 

Besides synthesizing a molecular pore of a definite diameter. supramolecular pore formation provides an attractive alternative. This methodology is also adopted in Nature for the formation of the and acetylcholine receptor channels as homotetrarner and heteropentamer. respectively. The assembly numbe of artificial supramolecular channels is generally not controlled, and various levels of conductance are usually observed. Two cholic acid methyl ether derivatives were connected via bisurethane linkages to obtain a membrane-penetrating component in its extended conformation. The carboxylate 3 and ammonium 4 head groups provide supramolecular... 

The conformation of the core cholic acid scaffold is curved with three hydroxyl groups on the a surface (Figure 19). The equatorial Ba-OH group is the least hindered, while the lla-OH is less hindered than the la-OH because of unfavorable 1,3-diaxial interactions between the 7q -OH and CH2 groups. The hydroxyl groups can themselves act as hydrogen-bond donors to bind anions however, it is possible to convert all or individual hydroxyl functional groups to amine or amide moieties to further... 

Cholic acid, an important constituent of human bile. Each six-membered ring is in a chair conformation. 

SYNTHESIS AND CONFORMATIONAL STUDIES OF A NEW HOST SYSTEM BASED ON CHOLIC ACID ... 

ABSTRACT. New synthetic hosts have been designed incorporating two molecules of cholic acid linked by a rigid diamine. Proton NMR studies indicate that the compounds exist in a rigid conformation with the steroid hydroxyl groups intramolecularly hydrogen-bonded. Heat or addition of methanol leads to conformational isomerism due to insertion of methanol into the cavity. 

Bujtas, K., T. Cserhati and J. Szejtli - Reduction of phytotoxicity of nonlonlc tensldes by cyclodextrins Burrows, C. J. and R. A. Sauter - Synthesis and conformational studies of a new host system based on cholic acid... 

Draw the most stable conformations of cholic acid and fusidic acid (Steroids-1). Describe the stereochemistry at each ring junction and the conformation of each six-membered ring. (Steroids-1)... 

Hassler et al. used MES-PSD with ATR-IR to study the receptor/ligand binding of human serum albumin (HSA) with a cholic acid (cholate) [21]. Phosphate-buffered saline (PBS) with cholate was modulated with neat PBS. The modulation experiments showed, for the first time, that the cholate binding induced a conformational change in the HSA with an increase in alpha-helical content. 

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