Phenolic hydroxyl function

Isotope labeling by derivative formation with deuterated reagents is useful for the preparation of analogs such as dg-acetonides, da-acetates, da-methyl ethers, dg-methyl esters, etc. The required reagents are either commercially available or can be easily prepared. (The preparation of da-methyl iodide is described in section IX-F. Various procedures are reported in the literature for the preparation of dg-acetone, da-diazometh-ane57.i63.i73 and da-acetyl chloride. ) These reactions can be carried out under the usual conditions and they need no further discussion. A convenient procedure has been reported for the da-methylation of sterically hindered or hydrogen bonded phenolic hydroxyl functions by using da-methyl iodide and sodium hydroxide in dimethyl sulfoxide solution. This procedure should be equally applicable to the preparation of estradiol da-methyl ether derivatives. 

The organic fraction composition may influence the exchange capacity. A key contribution to the exchange capacity of humus is given by the carboxyl and phenolic hydroxyl functional groups. Under appropriate pH conditions, uranic acids in polysaccharides or carboxy-terminal structures in peptides can contribute to the... 

Derivatives with a C-5 ethyl or propyl group (8 and 12) are particularly potent and these substituents can partly compensate for the lack of a phenolic hydroxyl function, normally a prerequisite for high activity (Table 5.2. cf. Nos. 3, 4 and 17). When R in metazocine (a- (X), R = R = R = Me) is replaced by hydrogen. 

The 8-0-methylepioritin-4a-ol (114) complements the rare series of flavan-3,4-diols where 0-methylation had occurred at one of the phenolic hydroxyl functions (Figure 11.10). Compounds 115-122 were obtained from various Lonchocarpus species. 

This is a large group of structurally diverse naturally occurring compounds that possess at least a phenolic moiety in their structures. Eor example, umbelliferone, a coumarin, has a phenolic hydroxyl functionality at C-7 quercetin is a flavonoid that has four phenolic hydroxyls at C-5, C-7, C-3 and C-4. Although the phenolic group of compounds encompasses various... 

Physical Properties. The molecular weight of dalbaheptides ranges from about 1150 to 2200. Pure dalbaheptides are obtained as colorless or whitish amorphous powders that usually retain water and solvents. Dalbaheptides are generally water-soluble. Teicoplanin can be obtained as an internal sail or as a partial monoalkaline (sodium) salt depending on tile pH of the aqueous solution in the final purification step. Other dalbaheptides arc obtained as acidic salts, such as hydrochlorides (vancomycin, actaplanin) or sulfates (ristocetin A, avoparcin, eiemomycin). The presence of amino, carboxyl, benzylic, and phenolic hydroxyl functions, sugars, and aliphatic chains influences both water solubility and total charge. 

The presence of a phenolic hydroxyl function in the 8 (or 21) position of benzomorphans, as a general rule, increases analgesic potency/1,33) This change is in parallel with changes in biological response observed for morphine and morphinans. Conversion of hydroxyl to methoxyl results in a significant reduction in analgesic response, whereas acetylation of the phenolic function usually increases activity/75 ... 

The tyrosine phenolic hydroxyl function was readily methylated to form a methyl ether under aqueous conditions at pH 10 with the proteins... 

Descretamine, C19H21O4N (mp 221°-224° [ ]d —368° in pyridine), eontains two methoxyl groups and two phenolic hydroxyl functions. Methylation with diazomethane gave (— )-tetrahydropalmatine, which implies that descretamine is a bisdemethyl (— )-tetrahydropalmatine (see Section X) isomeric with (— )-scoulerine (XLVI). At the time of writing the location of the hydroxyl groups has not been determined. 

Table 13.10 Bioisosteric replacements of the phenolic hydroxylic function...

The flavonoid structure consists of 2 aromatic rings (namely A and B in Fig. la) connected by a pyrane moiety (C). The presence of several phenolic hydroxyl functions within the ring classifies flavonoids in different families, including flavones, flavanols, isoflavones and flavonols, the latter characterized by a 3-hydroxypyran-4-one ring (Fig. lb). 

To circumvent this uncertainty without use of the caesium salt procedure, hydroxymethyl [87] or aminomethyl functions on the polymer can be reacted with carboxylic partners in an esterification reaction [207] or peptide bond formation with the aid of condensing agents like carbonylbisimidazole [88], dicyclohexylcarbodiimide [89] or others. For this purpose in the author s laboratory the use of symmetric anhydrides [3] of the N-protected amino acids to be attached to the support was found to be most effective [90], especially in the formation of activated esters on the gel phase with phenolic hydroxyl functions [38]. By this procedure, on 0.5% cross-linked polystyrenes, load levels up to 1.5 millimoles/g of the support are reached. 

The chances of using the specific distribution of flavonoid compounds either for the identification of the origin of a citrus product, or for clarification of taxonomy (as Swingle suggests), will depend on the development of easy methods of identification. With such completely meth-oxylated compounds as nobiletin and tangeretin this is not an easy matter, because of the absence of any phenolic hydroxyl function. For... 

The benzo-crown ether 22 and its ntq>htho-analogue were synthesized from the corresponding 6-bromo-6-deoxy-derivatives by azide ion displacement. They are able to sequester dopamine presumably with the assistance of hydrogen bonding between the 6-amino-group and the phenolic hydroxyl functions on dopamine. ... 

In the chemistry of protective groups, ethers and acetals are also often employed as protective groups of phenolic hydroxyl function under highly basic conditions. In practice, the living anionic polymerization of the ether- or acetal-protected monomers Id-lg (Figure 2) was possible under the same conditions in THF at -78 On the other hand, quanti-... 

This stability is confined to the FAD-peptide Tyr-Thr-Cys(FAD)-Tyr and it has been suggested (89), that either adenylate or tyrosine residues, or both, bring about stabilization through complexation in a way which has not yet been defined in chemical terms. In the opinion of the present author, the thermodynamic stabilization due to formation of molecular complexes should be minimal, while kinetic stabilization seems not to apply. Thus, formation of a macrocyclic thioacetal, possibly with the phenolic hydroxyl function of tyrosine (or with the threonine hydroxyl group) would better explain the unusual stability. 

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