Hydroxyl groups, aliphatic

The epoxidation is generally conducted in two steps (/) the polyol is added to epichlorohydrin in the presence of a Lewis acid catalyst (stannic chloride, boron triduoride) to produce the chlorohydrin intermediate, and (2) the intermediate is dehydrohalogenated with sodium hydroxide to yield the aliphatic glycidyl ether. A prominent side-reaction is the conversion of aliphatic hydroxyl groups (formed by the initial reaction) into chloromethyl groups by epichlorohydrin. The aliphatic glycidyl ether resins are used as flexibilizers for aromatic resins and as reactive diluents to reduce viscosities in resin systems. 

Hydromorphone [466-99-9] (31) and hydrocodone [125-29-1] (32) are isomers of morphine and codeine, respectively. Hydromorphone can be prepared by catalytic rearrangement of morphine (49) or by oxidation of the aliphatic hydroxyl group of dihydromorphine (50). Hydrocodone can be similarly prepared. As an antitussive, hydromorphone is several times more active than morphine and hydrocodone is slightly more active than codeine. Hydromorphone has a much higher addiction potential than hydrocodone. 

Since a few protective groups cannot satisfy all these criteria for elaborate substrates, a large number of mutually complementary protective groups are needed and, indeed, are becoming available. In early syntheses the chemist chose a standard derivative known to be stable to the subsequent reactions. In a synthesis of callistephin chloride the phenolic —OH group in 1 was selectively protected as an acetate. In the presence of silver ion the aliphatic hydroxyl group in 2 displaced... 

Side reactions involving branching through a secondary hydroxyl group can also occur. The extent of these side reactions should decrease as the ratio of epoxy to phenol decreases since phenolate anions are significantly more nucleophilic titan aliphatic hydroxyl groups. 

O-acetylation of the aliphatic hydroxyl groups of the ribose moiety (or other sugar moieties) to the 2, 3, 5 -tri-0-acetates ... 

A fourth important pharmacophoric element was established for the non-classical cannabinoid series in the form of a southern aliphatic hydroxyl group. Addition of this group to (192) resulted in the high-affinity CBi and CB2 receptor full agonist CP 55,940 (193) [129, 133], the tritiated form of which was used to first demonstrate specific cannabinoid binding sites in brain tissue [134]. Its enantiomer, CP 56,667 (194) has lower affinity for the CBi receptor (Table 6.17). 

Aliphatic hydroxyl groups cannot normally be selectively modified except in certain special cases such as the serine proteinases. In anhydrous formic acid, the A,O-acyl migration that occurs in strong sulfuric or phosphoric acid apparently does not occur. Instead there is formylation of the serine and threonine residues (208). Enzymically inactive aggregates are produced, but the reaction is reversed in aqueous solution at neutral pH and the activity returns. Josefsson reported the introduction of 29 formyl groups in RNase (209) as compared to the total of 25 Ser and Thr residues. This identification of reaction sites is not clear, however, since the number of formyl groups introduced into lysozyme far exceeded the Ser-Thr total. 

The lignin model compounds selected for this study possess two functional groups, a phenolic hydroxyl group, and an aliphatic hydroxyl group located on the side chain para to the phenolic hydroxyl group. Experiments were performed to determine the effect of blocking each of these two sites relative to the formation of chromophoric structures. 

From these results, it can be concluded that blocking the aliphatic hydroxyl groups does not inhibit the reactions of the model compounds in alkaline solutions leading to color formation. 

The reaction of EDTN [1-ethoxy-A dichloro-sym.-triazinyl) naphthalene] with the primary hydroxyl group of corticosteroids has been utilized for the sensitive determination of small amounts of these compounds [108]. The reagent reacts with phenolic hydroxyl groups but not with secondary aliphatic hydroxyl groups for example, testosterone does not react. 

One feature of the hydroxypyranones that presented a major challenge was the poor translation of high intrinsic inhibitory potency against the enzyme into antiviral activity in cell culture (Prasad et al., 1996). The acidic character of the enolic hydroxy group (pAa 4.2-6.5) as compared with aliphatic hydroxyl groups found in other classes of inhibitors did not appear to offer an explanation in as much as inhibitors of the pyranone class penetrate cells efficiently (Vara Prasad et al, 1995). Empirically,... 

Hydroxypyridines are readily alkylated under a variety of conditions. Mitsunobu reaction with alcohols occurs selectively at oxygen in the presence of PPh3 and DEAD in THF at room temperature <2003TL725>. The 3-hydroxy group may be selectively alkylated in the presence of aliphatic hydroxyl groups. Pyridine 104 is alkylated at the aromatic position with dodecyl bromide in the presence of potassium carbonate in DMF at 95 °C <20030BC644> (Equation 70). 

Sabljic et al. (1990), using 50 data points for 15 diverse organic chemicals, found a good correlation of Kcw with third-order valence molecular connectivity (3%v) and the number of aliphatic hydroxyl groups (N0Haliphatic) ... 

Fig ( 18 ) A series of reactions are carried out for the conversion of dehydroabietic acid to ketone (155) to hydroxymethyiation, protection of aliphatic hydroxyl group, addition of an -benzyloxymethyl group and acid treatment provides (156) which is con verted to (158). The butenolide function is constructed by successive oxidation and debenzylation to yield (159) which is converted to triptolide (149) by conventional methods. 

The aliphatic hydroxyl groups of threonine and serine side chains generally are modified by reagents that modify phenolic hydroxyls, but only under more severe conditions. However, once formed, the products are more stable than those with the phenolic hydroxyl. 

Strong chemical bonds between the adhesive and adherend help stabilize the interface and increase joint durability. Aluminum joints formed with phenolic adhesives generally exhibit better durability than those with epoxy adhesives. This is partially attributable to strongly interacting phenolic and aliphatic hydroxyl groups that form stable primary chemical bonds across the interface. 

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