2-hydroxy acids Subject

The synthesis of (-t-)-benzoylselenopederic acid (569) (477) (Scheme 71), the left-hand half of pederin (147), began with (-f-)-3-keto imide 570, which was subjected to the recently developed syn-directing Zn(BH4)2 reduction (482) to give 5yn-a-methyl-3-hydroxy acid derivative 571. Imide 571, after protection of the hydroxyl group as the THP ether, was reduced with DIBAH, and the resulting aldehyde was treated with lithium enolate of tm-butyl acetate to give the p-... 

All natural waxes are subjected to refining and branched hydroxy acids. Straight-chain, ... 

In a small test group of only five subjects erosion times of the dry skin of the calves were determined before and after four weeks of treatment with either a water-in-oil cream or a 12% lactic acid lotion (Figure 37.1). The assay was performed on four adjacent spots per leg. Spot-to-spot variation was on average less than one minute. In the majority of subjects erosions formed within two minutes. Erosion times on the legs treated with the water-in-oil cream were strongly increased, whereas the opposite legs, treated with the lactic acid lotion showed only slight improvement. This is not unexpected since alpha-hydroxy acids are known for their keratolytic activity which will weaken the... 

Subjective irritation is believed to be the most common cause of sensitive skin and cosmetic reactions.2 Propylene glycol, butylene glycol, and hydroxy acids are examples of subjective irritants present in modern-day cosmetics.2 12 Alcohol is also capable of causing subjective irritation, but is... 

Enantioselective synthesis ofa-hydroxy acid derivatives. Recently, Aggarwal has reported an enantioselective approach to the synthesis of a-hydroxy acid derivatives using trans- 1,3-dithiane- 1,3-dioxide. For example, reaction of trans-1,3-dithiane-1,3-dioxide with an aromatic aldehyde liberates the alcohol which is protected as the tetrahydropyranyl (THP) ether the resulting product may then be subjected to a Pummerer reaction, using trifluoroacetic anhydride, to give a thiolester. Transthiolesterification of this product using LiSEt gives the... 

Deracemization of mandelic add with the combined action of two enzymes has been reported. rac-MandeUc acid is acylated by a Pseudomonas sp. lipase in diisopropyl ether. After solvent removal the mfacture of mandeUc acid enriched in the R-form and the 0-acetyl derivative of the S-configuration are subjected to the mandelate racemase-catalyzed racemization in aqueous buffer. In these conditions only the non-acetylated hydroxy acid is racemized. In order to obtain (S)-0-acetylmandelic acid in an 80% isolated yield and a >98% e.e. the process must be repeated four times [9]. 

A15.1.1.2 Lactones. Hydroxy acids (HO—(CH2)s—CO—OH), are compounds that contain both a hydroxyl and a carboxylic acid function within the same molecule, and have the capacity to form cyclic esters called lactones (refer to Figures A15-1 and A15-2). Lactones are subject to general acid- or base-... 

The complex formation between Ni(ii) and acetate ions in aqueous solution has been studied by C NMR. Equilibrium quotients (132) and rate parameters (133) for the ligand exchange processes are reported. Complexes of hydroxy-acids (134) and iminodiacetates RN(CH2C0 )2 (135) have been the subjects of further studies. Co(ii) complexes of malate, citrate, isocitrate, and monomethylcitrate all exhibit large shifts which may be accounted for by assuming a common structural unit [22] in which the ligand is tridentate. Nickel(ii)... 

Stereospecific reductions of a-keto acids are well documented. l- and D-lactate dehydrogenases from common mammalian or bacterial sources are available for this purpose. By using a preselected l- or d-LDH, the preparation of a (2S)- or (2/ )-hydroxy acid of >99% ee can be virtually assured. The structural range of a-keto acids (29) that has been subjected to preparative-scale reductions to hydroxy acids... 

Amines. Chiral a-amino acids are obtained from cyanohydrins via a Mitsunobu reaction employing A-f-butoxycarbonyl-A-(2-trimethylsilyl)ethylsulfonamide as the nucleophile. The a-aminonitrile derivatives thus generated are hydrolyzed with acid. By means of an intramolecular displacement (3-hydroxy acids are transformed into (3-amino acids. Thus, subjecting the derived 0-benzylhydroxamides to Mitsunobu reaction conditions leads to (3-lactams which are readily processed (LiOH H, Pd/C). 

GBL was found to hydrolyse rapidly in plasma, with a half-life of approximately 1 minute. In spite of this rapid biotransformation, oral activity of GBL was almost identical to that achieved after intravenous administration of GHB. Apparently, GBL is not subjected to any of the processes which decrease peak plasma concentrations, viz gastrointestinal degradation, capacity-limited transport and first-pass metabolism. The use of lactone analogs as a general approach to improve the bioavailability and/or rate of absorption of other hydroxy-acids, e.g. prostaglandins, has, however, not been tested. 

Corey later described a modification of several steps of his earlier synthesis (see Scheme 1.32). Diacid 171 was smoothly decarboxylated in quantitative yield to give the mono acid 179, which was a-oxygenated as in the previous route. The resulting hydroxy acid 180 was then subjected to oxidative... 

Figures 5.7-5.9 were synthesized. Pen III (129) is a metabolite of Penicillium funiculosum isolated as a fruiting inducer against Schizophyllum commune. Its synthesis was carried out, as shown in Figure 5.7, employing Garner s aldehyde (D) as a starting material.13 The aldehyde D is not so unstable, and does not racemize easily. For the preparation of (-R)-hydroxy acid C, ( )-C was subjected to asymmetric acetylation with vinyl acetate in the presence of lipase PS.13...

The interaction between the sodium salt of phenylacetic acid and isopropyl magnesium bromide results into a doubly charged species known as the Ivanov reagent. This product on treatment with cyclopentanone affords aldol condensation to yield the corresponding hydroxy acid. The resulting product on being subjected to alkylation with N-(2-chloro-ethyl)-dimethylamine gives the desired official compound. 

Methyldihydrotestosterone on being subjected to bromination followed by dehydrobromination gives rise to the formation of 1,2-dehydro derivative, which upon ozonization and hydrolysis yields an aldehyde-acid (1). The resulting acid (1) on reduction produces the corresponding hydroxy-acid (11) which when lactonized produces the desired compound, oxandrolone. 

In view of this, the isolation of the isoeremane (181) and the cyclic ether (199) from collections of E. fraseri poses interesting chemical and biogenetic questions. These compounds would appear to be artefacts of the isolation/purification procedures. Certainly, the eremane-isoeremane conversion is difficult to prevent. However, the cyclic ether (199), whose chemical precursor (187) is known as a natural product, could not be obtained by subjecting the hydroxy acid (187) to conditions used in the isolation of the ether. Thus prolonged exposure of the hydroxy acid to acidified charcoal or silicic acid resulted in the formation of the isomer (iso-187) only (125). In any event, the formation of 199 suggests that the eremanes do not necessarily represent a biosynthetic terminus in Eremophila species. 

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