Lactones structure

Note D-Gluconic acid and other aldonic acids exist in equilibrium with lactone structures. 

Chromatography. A number of HPLC and TLC methods have been developed for separation and isolation of the brevetoxins. HPLC methods use both C18 reversed-phase and normal-phase silica gel columns (8, 14, 15). Gradient or iso-cratic elutions are employed and detection usually relies upon ultraviolet (UV) absorption in the 208-215-nm range. Both brevetoxin backbone structures possess a UV absorption maximum at 208 nm, corresponding to the enal moeity (16,17). In addition, the PbTx-1 backbone has an absorption shoulder at 215 nm corresponding to the 7-lactone structure. While UV detection is generally sufficient for isolation and purification, it is not sensitive (>1 ppm) enough to detect trace levels of toxins or metabolites. Excellent separations are achieved by silica gel TLC (14, 15, 18-20). Sensitivity (>1 ppm) remains a problem, but flexibility and ease of use continue to make TLC a popular technique. 

The difference in structure between 16 and 17 is readily understood in terms of the addition of strongly electron-donating substituents, but the contrast between 16 and 20 is less easily rationalized. Photolysis of 19 was carried out in HFIP (dielectric constant (e) = 16.75), while TRIR experiments with diphenyl diazomethane (22) were carried out in dichloromethane (e = 9.08), suggesting that a-lactone structure may be dependent on solvent polarity. 

A different approach for the modification of the basic Malachite Green lactone structure has been the replacement of one 4-dimethylaminophenyl group by electron-rich heterocycles. The most thoroughly investigated heterocycle has been the 3-indolyl residue, which may be introduced by two different routes as shown in Scheme 7. 

The possibility of replacing all three phenyl rings in the triarylmethane lactone structure by heterocycles has also been exploited. The first compound to be described83 was the 3,3-bisindolyl-7-azaphthalide (18). This... 

The lactone structure is a versatile synthetic intermediate that can be used to access a variety of 4-substituted pipecolic derivatives. Hydrogenolysis in meth-anolic HCl, followed by hydrolysis and desalting, gave 4-hydroxypipecolic... 

Ivle, G. W. Wltzel, D. A. "Sesquiterpene Lactones Structure, Biological Action, and Toxicological Significance", In press. 

There are also a few /3-lactone structures in natural products. Two toxic compounds, anisatin and neoanisatin, were isolated from a toxic plant, Japanese star anise, and have been assigned to the /8-lactone-containing structures (72) and (73), respectively. These structures are based on extensive study of spectral data and chemical transformations (68T199). 

Lactone structures have recently been determined for two microbial metabolites which have antibiotic properties. Antibiotic 1233A (77) was the first /8-lactone to be isolated from a fungus. Esterastin (78), an inhibitor of esterase, is produced by a strain of Streptomyces (71JCS(C)3888, 78MI51300). 

Isolation of a lactone, structurally related to the esterifying acids of pyrrolizidine alkaloids, from the costal fringes of male Ithomiinae. Journal of Chemical Ecology 2 263-270. 

Name of aldono-l,4-lactone Structure Starting Material Ref-... 

Studies of molecular spectra (UV, IR and NMR) are potentially useful in providing information about aromaticity. Further information may be obtained from magnetic susceptibilities and dipole moment measurements. The UV spectra of pyran-2-one and some of its analogues have been reported (71PMH(3)67), and are consistent with the enol lactone structure (17). 

The available evidence suggests that the heterocyclic ring in compounds (19), (28) and (206) is not markedly aromatic. Much of the chemistry of coumarins can be rationalized in terms of a benzo-fused enol lactone structure. 

In a later paper (81TL1749) the same group has shown that the lactone structure is not a prerequisite for chromone formation, since the enol ester (478) yields a chromone on irradiation. ... 

Dimeric aldoketenes and ketoketenes of p-lactone structure show a chemical behavior which is not much different to that of diketene. Thus nucleophiles add in similar fashion to give derivatives of 3-ketoacids which are mono- or dialkylated at C-2 (aldo- and ketoketene dimers, respectively), but the reaction can often be slower than with the parent compound and, in case of long-chain or bulky substituents, may not proceed at all. Other reactions can proceed differently than those with diketene. For an overview of important reactions of aldoketene and ketoketene dimers see Reference 122. 

The alkaline hydrolysis of the compounds (118)-(123) in 70% (v/v) dioxane-water at various temperatures has been investigated.101 Intramolecular catalysis by the neighbouring carbonyl group occurs in the alkaline hydrolysis of (118)-(121) and the alkaline hydrolysis of (122) and (123) is rapid owing to their lactone structures. The hydrolyses of C-terminal amides of a-amino acids was dealt with earlier.56 Also, the acid-catalysed cleavage of A-(2-aminophcnyI)phthalamic acid (82) was discussed earlier.72... 

Decarboxylation of pyruvic acid and its isomers, including the enol tautomers and enantiomeric lactone structures, has been investigated at the B3LYP/6-311+- -G(3df, 3pd) level.18 It has been found that a keto form with trans CmethyiCketoCacidOhydroxyi and cis CketoCacidOH, and with one methyl hydrogen in a synperiplanar position with respect to the keto oxygen, is the most stable. 

Veracevine (11), cevine (15), or cevagenine (14) may be oxidized with bismuth oxide to the same 8-lactone (27) (45,52). This undergoes the simple reactions shown in Scheme 7 to give the other five-membered ring A derivatives 28-31. Two natural products (32,33) having five-membered A rings and 8-lactone structures have been isolated and are recorded along with their synthetic derivatives in Table IX. 

Schmidt, T. J. 1999. Toxic activities of sesquiterpene lactones structural and biochemical aspects. Curr. Org. Chem. 3, 577-608... 

The only reference to these compounds records the preparation of the furo[3,4-6]pyrazine-/V-oxides (247) from the oximes (246), which were intended to be used to make pyrazines for further elaboration into pteridines (Equation (84)). It is suggested that in an acidic environment the isopropylidene is cleaved thus allowing cyclization to the lactone structure <84JHC657>. 

---