A-mercapto acid

HYDROXYTHIAZOLE DERTVATIVES FROM NITRILES AND a-MERCAPTO ACIDS... 

Another class of new ligands was prepared in quantitative yields by Feringa et al., in 1997, by reaction between a-mercapto acids, aniline and 2-pyridine-carboxaldehyde." These pyridyl-substituted thiazolin-4-one ligands were further involved in the copper-catalysed conjugate addition of ZnEt2 to 2-cyclohexenone,... 

A logical extension of the synthetic strategy underlying our solid-phase approach toward 1,5-benzothiazepinones was to replace the [3-mercapto acids (cysteine, penicillamine) by a-mercapto acids, such as mercaptoacetic acid 54a or thiolactic acid 54b. This change would facilitate access to the corresponding [6,6]-fused systems, i, e. 1,4-benzothiazin-3-ones 57. As with the benzothiazepines, no solid-phase synthesis of benzothiazines has been reported to date. 

From a pharmaceutical discovery perspective, it could be fruitful to embark on a library synthesis using cyclic hydroxamic acid templates. There are several reports describing interesting bioactivities for such compounds, particularly as inhibitors of metal-dependent enzymes 48-52 However, only three a-mercapto acid monomers are currently available from commercial sources hence the structural diversity of products that could be easily prepared is limited. Several approaches to introducing additional points of diversity into the benzothiazinone scaffold are currently under investigation. 

Heterocyclization of a-mercapto acids with (azolylimino)indolones 182 (Scheme 36) afforded the spirocyclic thiadiazepinones 183 <1989IJB639, 1994PS27>. gem-Dithiol addition to bis(methylene)-substituted diketopiper-azine 168 afforded the bridged bicyclic structure 169 featuring two dithiazepane rings (Scheme 33) <1981JHC1545>. 

Resin-bouda-amino esters, besides being traditionally used for making peptides, have served as key intermediates for the construction of various heterocyclic scaffolds. Thus, they react smoothly with isocyanates to form ureas, which upon heating under acidic conditions cyclize to form hydantoins 53 [27]. A one-pot, three-component condensation of resin-bound a-amino esters with aldehydes and a-mercapto acids affords 4-thiazolidi-... 

The AA has also been used in the preparation of analogues of the paclitaxel side chain 32 like protected a,[3-diamino acids 35a and 35b from 33 [59,60], 0-amino-a-mercapto acids 36a and 36b from 33 [59,61], derivatives bearing a ni-... 

Reaction of a-mercapto acids with hexafluoroacetone gives the oxathiolanones 192 (Equation 62) <2003JHC435> which provide a useful protected form of the acid <2004S1821> and also allow introduction of a mercapto acid unit into peptides <2004S1088>. 

Extension of this synthetic strategy to the preparation of 1,5-benzothiazepin-4-ones and 4-alkyloxy-l,4-thiazin-3-ones by using suitably protected forms of cysteine and a-mercapto acids in nucleophihc aromatic substitution reactions of 7 has been envisaged by the authors. 

The reported synthesis and properties of poly(thiol esters) of the A-B and A-A/B-B types are reviewed for these classes of compounds 2 poly(a-mercapto acids), 7 poly(/3-mercapto acids), 4 poly (e-mercapto acids) and 44 A-A/B-B type poly(thiol esters). The melting points of poly(thiol esters) are generally lower than those of the corresponding polyamides and higher than those of the polyesters. They are readily hydrolyzed by alkali, which seems to be the main reason for the lack of commercial interest in these materials. 

Poly(a-mercapto acids). The simplest compound of this type is poly(thioglycolide) (VIII)—poly( -mercaptoacetic acid)—which has been prepared in different ways. 

Poly(a>-mercapto acids). Poly(a>-mercaptoheptanoic acid) (XXV) - (xn = 11, m.p. = 69°C) (19)—and poly(a>-mercaptoundecylenic acid) (XXVI)—[r/]25cHci3 = 26 ml/g (22)—were prepared from the [Pg.124]

Ytterbium triflate in an ionic liquid is an efficient catalyst for reaction of aldehydes and ketones with mercaptoethanol to form 2-substituted 1,3-oxathiolanes <04SL2785> and K-10 montmorillonite has been used for the same reaction where it shows selectivity for aldehydes over ketones <04SL1592>. The compound 76 has been used to introduce a mercapto acid unit into peptide analogues <04S1088> and the diastereoselectivity of addition of the anion of 77 to carbonyl compounds has been examined <03JHC979>. 

In contrast to the a-oxy- or a-amino-substituted allylic esters, not many examples for a-thio substituted substrates and their application in Claisen rearrangements are described so far (Scheme 5.2.63). Lythegoe et al. applied the Ireland-Claisen rearrangement to the synthesis of a-mercapto acids such as 199 starting from allylic esters 198 [116]. 199 was oxidized and further converted into a,j8-unsaturat-ed esters or subjected to an oxidative degradation. Jones et al. used the Ireland-Claisen rearrangement of 200 in their syntheses of thietan oxides [117]. 

The analysis of 4,4 -diacetoxy-5,5 -dimethyl-2,2 -bithiazolyl (96) has proved the general structures of the products of reactions between a-mercapto-acids and cyanogen on treatment with diazomethane. The molecule is centrosymmetric, and although both five-membered rings are planar,... 

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