With a-hydroxy acids

Tetramethylpiperidinomethyltrimehtoxysilane 816 and the corresponding 2,2,6,6-tetramethyl-piperidinomethylsilane 817 are the precursors for another family of spirocyclic silicates 818-824, which are accessible upon reaction with a-hydroxy acids, a-amino acids, o-benzene dithiol, and dithioglycol (Scheme 109).821 822... 

Other preparations of 2-iminothiazolidin-4-ones which are discussed in the review by Brown139 utilize the reactions of thiourea with a-hydroxy acids,146 ethyl diazoacetate,73 glycidic esters,74,147 cinnamic acid,148 unsaturated diacids (fumaric, maleic, and citraconic) or their esters or imides,149-152 and propiolic esters.153,154 There has been considerable controversy in the literature surrounding the propiolic ester synthesis since many workers have proposed that the products are 1,3-thiazines (see Section IV, B, 1). The pertinent papers in this controversy have been summarized by Cain and Warrener.155 Nagase158 has recently settled the argument in favor of the 2-iminothiazolidin-4-... 

In addition to the conversion into phosphonochloridates as described in Section 10.10.2.1.2, phosphonate monoacids can also be activated for coupling via some of the popular reagents from standard peptide chemistry, such as BroP, 77 BOP/ and PyBOP. 79 One-pot activation and coupling of hydrogen phosphinates with a-hydroxy acids is also possible via the method outlined in Section 10.10.2.1.3. 76 The procedure outlined in Scheme 19 illustrates an optimized procedure for coupling a hindered phosphonate 57 and an a-hydroxy acid derivative via the phosphonochloridate 72 ... 

Morpholine-2,5-diones have been prepared by intramolecular, nucleophilic cleavage of polystyrene-bound amino acids acylated with a-hydroxy acids (Entry 2, Table... 

With a-hydroxy acids chelation (Fig. 18) may help to form stronger complexes (higher k value) than for the corresponding monodentate... 

Van Scott, E. and Yu, RJ. Control of keratinisation with a-hydroxy acids and related compounds, Arch. Dermatol., 110, 586, 1974. 

Complcxation of the actinides by inorganic and organic ligands is very important for their chemical. separation and their behaviour in the environment. Examples arc the separation of trivalent actinides by complcxation with a-hydroxy acids and the high solubility of U(VI) due to complcxation with carbonate ions to give the tris-carbonato complex U02(C02)3 " found in seawater. 

Lesquerella. The only oil of significance with a hydroxy acid is castor oil (Section 5.1) but among the new crops being seriously developed are two containing hydroxy acids. Lesquerella oils have some resemblance to castor oil, but Dimor-photheca pluvialis seed oil contains a different kind of hydroxy acid. 

Elements of Group V Bonds to Oxygen.—Alcohol groups can be displaced from triethoxyarsine by oximes or diethylhydroxylamine in a stepwise manner to give the products (EtO)3-nAs(ON=CR1R2) .659 Two hew 1,3,2-dioxa-arsolans (92) result when tris(dimethylamino)arsine and either ethylene glycol or pinacol react, and further reaction of these compounds with a -hydroxy-acids leads... 

Depsipeptides are near-relatives of peptides, with one or more amide bonds replaced by ester bonds in other words, they are formed by condensing a-amino acids with a-hydroxy-acids in various proportions. There are several important natural examples of these, of defined sequence for example the antibiotic valino-mycin and the family of enniatin antibiotics. Structures of other examples of depsipeptides are given in Section 4.8. 

The stability order for Ti complexes with a-hydroxy-acids of glycolate > lactate > mandelate is not the order of base strength of the ligands. ... 

Functional mimic systems for the MnP enzyme will be discussed in Section V, Reactivity. An example of monomeric complexes prepared with a-hydroxy acids as functional mimics is presented in Section III.A.3 on monomeric structures. 

In these studies, the manganese complex was generated in situ from added manganese and ligand. In 1991, Saadeh et al. reported the preparation and isolation of complexes with a-hydroxy acids, for example lactic acid, 2-hydroxyisobutyric acid (HIB) and 2-hydroxy-2-ethylbutyric acid (HEB) (425). The latter two ligands led to Mn1 complexes with 06 first coordination spheres, whereas Mnin complexes were prepared and characterized with lactic acid. The crystal structure of the complex with HIB shows it to be two MnIVL2 units that are... 

Another common reaction with a-hydroxy acids such as LA is the selfcondensation under water-removal circumstances, forming lactoyl lactate, oligomers, or lactide - the cyclic di-ester of LA (6) [10, 41]. These condensation reactions are dehydrations and thus retain the full functionality in the molecule, while lowering the H index see Fig. 2. Moreover, the atom economy of 80% is high with only water as side-product. Lactide is the true industrial precursor of PLA and the atom economy of 80% is equally valid for PLA [42]. 

Mahrwald R. Titanium(lV) alkoxide ligand exchange with a-hydroxy acids the enantioselective aldol addition. Org. Lett. 2000 2 4011 012. 

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