Alicyclic acids

These considerations allow us to link the time required for humification (always directed to an increase in entropy) to the type of chemical transformations in humic system, which best suit this demand The system of NOM and HS should unavoidably evolve toward molecular compositions with the maximum number of isomers. Given that the overwhelming part of humic matter is being formed under oxic conditions, these structures are represented by low-molecular-weight aromatic and alicyclic acids. This suggests that under the same environmental constraints, the humification of NOM should lead to the formation of structures with an increased content of aromatic structures (or more precisely, the amount of DBE) and with a decrease in size similar to what was revealed by the results of data analysis on size-fractionated samples of humic materials shown in Figures 13.14A-D. 

Nielson1 has correlated the ultra-violet aBsorption spectra and the structure of a/ -unsaturated acids and their derivatives. For alicyclic and acyclic types, each alkyl substituent at the olefinic double bond produces a bathochromic shift of 8—10 m x. For alicyclic acids, an exocyclic double bond produces a bathochromic shift of 5 m/x. A 5 m/x shift is also produced by an endoeyclic double bond in a five- or seven-membered ring. Other factors which shift the Amax in these compounds have also been discussed. The usefulness of the correlation in structural elucidation has been illustrated. 

Esters of saturated and unsaturated branched-chain and alicyclic acids... 

Koshiba, T. Alicyclic acid metabolism in plants. 12. Partial purification and some properties of shikimate kinase from Phaseolus mungo seedlings. Plant Cell Physiol., 20, 803-809 (1979)... 

The main occurrence of cyclopentenyl fatty acids in seeds of Flacourtia-ceae suggests a function as an eneigy reserve to be utilized during germination. The degradability of these alicyclic acids by endogenous enzymes can be deduced from indirect evidence. In the course of jS-oxidation, aleprolic acid must be formed as an intermediate. It has been shown that exogenously added [l- C]aleprolic acid is readily catabolized (Cramer and Spener, 1976). 

This section is mainly concerned with the non-volatile, non-nitrogen-containing organic acids. It is restricted to the aliphatic acids and alicyclic acids (except for fatty acids, which are covered in Sect. 6.4.2) the aromatic acids, except for shikimic and quinic acid, are covered in Chap. 7. Since only a limited number of acids have been reported to occur in woody tissues such as bark and heartwood, the acids present in other parts, such as leaves and fruit, are also included. Those found only in herbs are excluded. No attempt has been made to search all the woody plants for the occurrence of these compounds. In the following, a brief introductory explanation about the bioformation and function in plants is described for the respective organic acids (10, 33, 43, 61, 120, 121), and this is followed by tables listing the occurrence of the acid in woody plants, if any. 

Madhusudanamma W, Sastry K N S, Rao V, Sundara S, Santappa M 1978 Studies on casuarina (Casuarina equisetifolia). I. Isolation and characterization of alicyclic acids, polyols and amino acids from the different parts of casuarina. Leather Sci 25 369-371... 

The most important alicyclic acid derived from tetrahy-droxycyclohexane is (3 R,5 R)-l,3,4,5-tetrahydroxycyclohexane-l-carboxylic acid known as (—)-L-quinic acid. The trihydroxycy-clohexene derivative is (311,4S,511)-3,4,5-trihydroxycyclohexene-l-carboxylic acid known as (—)-L-shikimic acid (see 8-71). 

Alicyclic acids, quinic acid and shikimic acid (intermediates in the biosynthesis of phenylalanine, tyrosine and tryptophan, numerous flavourings, natural colourings and other compounds), are common compounds in foods. They occur as free compounds and also in the form of various derivatives, for example in depsides such as chlorogenic acids (8-82). 

Several tracer studies of the biosynthesis of (—)-shikimic acid in higher plants have been made and these all accord with the view that, as in micro-organisms, the seven-carbon skeleton of the alicyclic acid is derived by an initial condensation of D-erythrose-4-phosphate (7) and phosphoenolpyruvate (8), Figure 1.2. Uniform labelling of (—)-shikimic acid was obtained by exposure of living plant tissues to carbon dioxide for extended periods " . Short-term exposure gave (—)-shikimic acid with 25 per cent of the isotope in the carboxyl group . This was rationalist on the basis... 

A further pathway of biosynthesis of salicylic acid (97) may involve its formation from the unusual alicyclic acid (102) wtiich is found in the glucosides tremulacin (101) and salicortin (100) which have been isolated from Populus tremuloides and Salix purpurea... 

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