Thiazolidines formation

The number of reactions required for total biosynthesis and chemical synthesis of yersiniabactin (24) is comparable, with 22 [62] and 30 [76, 77] reactions, respectively. However, two very different strategies are used by nature and by chemists in the production of this compound. The enzymatic pathway biosynthesizes the siderophore in a linear manner, while the chemical route convergently synthesizes two molecular halves and condenses them to the final product. The number of steps required for thiazolidine formation in the chemical synthesis of... 

Since direct analyses for formaldehyde and methyl glyoxal are difficult with gas chromatography (GC) or any other methods, we attempted to determine levels of formaldehyde and methyl glyoxal in various food samples using their derivatives thiazolidine and 2-acetylthiazolidine, respectively. The proposed mechanism of thiazolidine formation from cysteamine and corresponding aldehydes is shown in Figure 1. 

Thiazolidines. formation, 168-169 Tricyclic alkaloids, 242-251 coccinellines, 245, 246-247 cyclopenta[b]quinolizidines. 247-249 gephyrotoxins, 242-245 pynolizidine oximes, 249-251 Trypargine, 262-263... 

The aromatic ring of oestradiol or oestrone methyl ether readily forms a tricarbonyl chromium (0) complex in which the 13C signals from the aromatic ring are shifted strongly upheld (by ca. 14—34 p.p.m.). Smaller upheld shifts for other carbon atoms close to the aromatic ring (e.g. 2 p.p.m. for C-6) have been used to settle uncertainties in the earlier literature concerning the assignments of individual 18C resonances.69 13C N.m.r. spectra discriminate between A4- and A5-isomers of spiro-3-steroidal ketone derivatives thiazolidine formation results only in the (3i )-isomer (12), whereas hemithioacetals are mixtures of the (3R)- and (35)-forms.80... 

Previous work has demonstrated that sugars that show highest conversion to thiazolidines in dieir reaction widi cysteine produce also most browning and flavor (5). This looks contradictory since the formation of thiazolidines is seen as the cause of browning inhibition. To explain these results, it was assumed that the padiways to thiazolidine formation as well as to browning and flavor formation proceed via the same intermediate, which is the Schiffs base of cysteine witii the carbohydrate. 

Figure 3. Thiazolidine formation in ligation site by two steps. (A) Oxidation of a C-terminal 1,2-propanediol peptide or an N-terminal serinyl peptide by NalOt to form a C-terminal or an N-terminal peptide aldehyde, respectively. (B) An aldehyde ligated with an /V-cysteinyl peptide to form a thiazolidine peptide with different orientations of the thiazolidine ring.

In his cephalosporin synthesis methyl levulinate was condensed with cysteine in acidic medium to give a bicyclic thiazolidine. One may rationalize the regioselective formation of this bicycle with the assumption that in the acidic reaction mixture the tMoI group is the only nucleophile present, which can add to the ketone. Intramolecular amide formation from the methyl ester and acid-catalyzed dehydration would then lead to the thiazolidine and y-lactam rings. The stereochemistry at the carboxylic acid a-... 

Formaldehyde from cigarette smoke is collected by trapping the smoke in a 1-L separatory funnel and extracting into an aqueous solution. To aid in its detection, cysteamine is included in the aqueous extracting solution, leading to the formation of a thiazolidine derivative. Samples are analyzed... 

Thiazolines and thiazolidines may also be prepared in this fashion, the structure of the final product determining the substitution pattern to be chosen in the reaction components. Reaction of ethyl bromoacetate with the substituted thioamide (71) resulted in formation of the thiazolidin-4-one (72) (70KGS1621). 

By virtue of their fused /3-lactam-thiazolidine ring structure, the penicillins behave as acylating agents of a reactivity comparable to carboxylic acid anhydrides (see Section 5.11.2.1). This reactivity is responsible for many of the properties of the penicillins, e.g. difficult isolation due to hydrolytic instability (B-49MI51102), antibacterial activity due to irreversible transpeptidase inhibition (Section 5.11.5.1), and antigen formation via reaction with protein molecules. 

Reactions between A -(l-chloroalkyl)pyridinium chlorides 33 and amino acids in organic solvents have a low synthetic value because of the low solubility of the amine partner. A special protocol has been designed and tested in order to circumvent this drawback. Soon after the preparation of the salt, an aqueous solution of the amino acid was introduced in the reaction medium and the two-phase system obtained was heated under reflux for several hours. However, this was not too successful because sulfur dioxide, evolved during the preparation of the salt, was converted into sulfite that acted as an 5-nucleophile. As a result, A -(l-sulfonatoalkyl)pyridinium betaines such as 53 were obtained (Section IV,B,3) (97BSB383). To avoid the formation of such betaines, the salts 33 were isolated and reacted with an aqueous solution of L-cysteine (80) to afford thiazolidine-4-carboxylic acids hydrochlorides 81 (60-80% yields). 

Recently, Tam et al. extended their orthogonal ligation concept, using the thermodynamically driven formation of a thiazolidine ring for the synthesis of dendritic compounds that carry cyclic peptides at the surface, which were designated multiple cyclic antigen peptides (McAPs) [18,19]. 

A. M. Davis, N. J. Layland, M. I. Page, F. Martin, R. M. O Ferrall, Thiazolidine ring opening in penicillin derivatives. Part 2 Enamine Formation , J. Chem. Soc., Perkin Trans. 2 1991, 1225-1229. 

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