Hydroxyl substitution effect

Hydrogenation of 19-hydroxy-3a- and 3j5-substituted-A -steroids over platinum or rhodium yields increased amounts of 5j9-products as compared to the corresponding 19-desoxy series (hydroxyl group effect). In contrast, the A -19-carboxaldehyde (27) gives only the 5a-product when hydrogenated over either palladium or platinum. ... 

It was shown that the protonation regioselectivity was strongly controlled by methoxy and hydroxyl substituents, whose directive effects overwhelmed the methyl substitution effects." Regiocontrol by —OMe and —OH substituents, and its stronger influence relative to methyl groups, was also observed in the nitration and bromination reactions (Fig. 21). Regioselectivities observed in the nitration and bromination reactions in representative cases were the same as those via protonations. 

Chirahty transmission can also be induced in thio-Claisen reactions by a chiral center adjacent to the allyl vinyl sulfide core. The group of Metz-ner examined the diastereoselectivity of the rearrangement of acyclic S-allyl ketene dithioacetals bearing a chiral center adjacent to carbon 6. hi these substrates, the sigmatropic shift proceeded smoothly and with modest syn anti diastereoselectivity [74]. In contrast, higher selectivities are foimd for thio-Claisen precursors bearing a chiral center adjacent to carbon 1 mainly due to steric effects and allylic strain [75]. In 1991, the group of Beslin examined the effect of a hydroxyl substituted chiral center attached to C-1 of Z and E S-allyl ketene dithioacetals [76,77] (Scheme 7). Under the reaction conditions, these... 

A rare substitution hydroxylation is effected by Fusarium solani, which converts o-hydroxy-cis-cinnamic acid into 4-hydroxycoumarin (equation 473) [1089]. 

Foltyn EM, Clinard FW Jr, Rankin J, Peterson DE (1985) Self-irradiation effects in Pu-substituted zirconolite II. Effect of damage microstractrrre on recovery. J Nucl Mater 136 97-103 Frondel C (1958) Hydroxyl substitution in thorite and zircon. Am Mineral 38 1007-1018 Froude DO, Ireland TR, Kirmey PD, Williams IS, Compston W, Wilhams IR, Myers JS (1983) Ion microprobe identification of 4,100-4,200 Myr.-old terrestrial zircorts. Natrrre 304 616-618 Gibbons JG (1972) Ion implantation in semiconductors— Part II Damage production and armeahng. Proc IEEE 60 1062-1096... 

Beckett and his co-workers (B14) examined the hydrolysis by purified horse serum cholinesterase of a number of analogs of butyrylcholine. The introduction of an a-methyl group into the choline moiety of the butyryl ester was found to decrease the rate of enzymic hydrolysis only slightly, whereas a drastic reduction was found for d-methyl substitution. The substitution of various functional groups into the butyryl moiety of butyrylcholine modified the affinity of the substrate for the enzyme. These results are summarized in Table 3. Since values can be assumed to be inversely proportional to affinity values, the results shown in this table indicate that j8-hydroxyl substitution increases the affinity of the substrate for the enzyme, and a,/3-unsaturation effects even greater affinity. Acetoacetylcholine has a greater affinity for the enzyme surface... 

Feeding studies using deuterated [1- 13C] acetate and subsequent location of the deuterated sites by the nmr isotope shift effects showed labeling at carbons 7 and 9. The absence of a detectable p-2H isotope shift at carbon 4a indicates that only one of the carbon-5 hydrogens is acetate-derived and that this is stereospecifically eliminated by carbon-5 a hydroxylation. 8-Methoxychlortetracydines, with and without hydroxyl substitution at carbon-4a, have been isolated. These tetracyclines retain the original oxygen at C-8 from the polyketide chain (79—81). 

N-substituted amino acids showed high capacity factors N-acetylated Phe and N-formylated Phe gave 6 and 10 times higher capacity factors than Phe in ACD-PW respectively, and 30 and 50 times higher in A-Me CD-PW. These N-substitution effects on retention behavior were also observed for a nonaromatic amino acid such as Ala. The capacity factors of N-substituted amino acids depended on the ionic strength of eluent. The dependency was observed clearly in A-Me-CD-PW. Methylation of hydroxyl groups on the CD ring enhanced the interaction with amino acids. 

Despite considerable efforts directed toward finding alternative side chains that will impart oral absorbability in cephalosporins, only D-(- )-arylglycyl- or dihydrophenylglycyl-substituted cephalosporin antibiotics possess significant oral absorption. Ampicillin, as well as a number of other penicillins without arylglycine side chains, are absorbed via the oral route. The effect of p-hydroxyl substitution in the phenylglycine side chain of ampicillin on its oral absorption is well documented. Za-rowny et al., (1974) have reported the absolute oral absorption of amoxicillin to be roughly twice that of ampicillin, Nayler (1971) reported that a m-hydroxyl substituent on ampicillin had a detrimental effect on its oral absorption in humans. 

The addition of a p-hydroxyl substituent to a phenylglycine cephalosporin had little effect on the in vitro activity. In some cases no changes in activity were noted, whereas in other cases slight decreases in activity were seen (Webber and Ott, 1977). Studies by Preston and Wick (1974) and Dunn et al., (1976) suggested, however, that as in the case of amoxicillin, addition of a p-hydroxyl substituent increased oral absorption in mice relative to unsubstituted phenylglycine cephalosporins. The addition of a m-hydroxyl substitutent has been reported (Dunn et al., 1976) to have a negligible effect on the oral absorption of some cephem antibiotics in mice. 

Eor instance, a glycol HO-X-OH shows no substitution effect in an esterification reaction if the reactivity of the hydroxyls in -COO-X-OH is the same a single kind of group -OH needs to be considered and the description of the reaction scheme is much simpler. 

Sainz-Diaz et al. (78) studied the isomorphous substitution effect on the vibration frequencies of hydroxyl groups in clay octahedral sheet by using ab initio calculations on cluster model of the clay mineral. They were not able to obtain calculated values of the OH vibration frequency of clay minerals matching experimental results because their simulation didn t include the hydrogen bonding between structural OH and apical oxygens. However, they claimed that then-model represents a relative behavior with respect to the isomorphous substitution of octahedral sheet cations similar to the experimental data. 

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