1 -aminocyclopropane-1 -carboxylic acid synthesis

The second chirality source used in the synthesis of aminocyclopropane carboxylic acids was D-glyceraldehyde acetonide, which after Wittig-Homer-Emmons reaction provided the alkenes 61. Treatment with diazomethane and subsequent irradiation at low temperatures alforded the cyclopropanes 62, which were converted into several other derivatives by modification of the side chain (Scheme 11). Notably, the best results were obtained by irradiating in the presence of benzophenone as triplet sensitizer [33, 34]. Following a similar synthetic procedure allocoronamic acid 65 was prepared, which is one of the amino acids that can be processed by plant tissues and promises the possibility to control the enzymatic processes underlying plant growth and fruit ripening [35]. 

A chiral aldol-retro-aldol-type introduction of a chiral auxiliary was applied to the cyclopropanation (Scheme 1.54) [89]. Chiral aldol 104 was first formed and then underwent stereoselective cyclopropanation to give 105. The basic treatment of 105 afforded chiral cyclopropane 106 in good yields with high enantiomeric excess. The three-step synthesis achieved enantiomerically pure cyclopropane. (15,2/ )-Cascarillic acid 107 was synthesized by this route. The asymmetric synthesis of aminocyclopropane carboxylic acid 108 has also been reported [90]. 

This version of the Curtius rearrangement has been applied to the synthesis of amino acid analogs and structures containing amino acids. Several m-2-aminocyclopropane carboxylate esters were prepared by selective hydrolysis of cyclopropane-1,2-dicarboxylates, followed by reaction with DPPA.267... 

Hot water treatment was reported to delay carotenoid synthesis and thus yellowing of broccoli florets (at 40°C for 60 min) and kale (at 45°C for 30 min), but did not affect Brussels sprouts (Wang 2000). Hot air treatment (38°C and 95% RH for 24 hr) slightly decreased lycopene and (3-carotene content in tomato fruit (Yahia and others 2007) however, fruit heated at 34°C for 24 hr and stored 20°C developed higher lycopene and (3-carotene than nonheated fruit (Soto-Zamora and others 2005). Moist (100% RH) hot air (48.5 or 50°C) for 4 hr caused injury to papaya and losses in lycopene and (3-carotene, but similar treatment with dry air (50% RH), alone or in combination with thiabendazole, had no effect on lycopene and (3-carotene (Perez-Carrillo and Yahia 2004). High-temperature treatment also suppressed 1-aminocyclopropane-l-carboxylic acid oxidase activity and thus indirectly prevented carotenoid synthesis (Suzuki and others 2005). 

Subsequently, the asymmetric synthesis of stereospecifically monodeu-terated 1-aminocyclopropane-l-carboxylic acids (IS, 2R) and (IS, 2S) has also been achieved by a modification of the above route (89JOC270). The essential step involves an intramolecular alkylation on a lactim ether anion (Scheme 64). 

Fig. 1. Ethylene biosynthesis. The numbered enzymes are (1) methionine adenosyltransferase, (2) ACC (l-aminocyclopropane-l-carboxylic acid) synthase, (3) ethylene forming enzyme (EFE), (4) 5 -methylthio-adenosine nucleosidase, (5) 5 -methylthioribose kinase. Regulation of the synthesis of ACC synthase and EFE are important steps in the control of ethylene production. ACC synthase requires pyridoxal phosphate and is inhibited by aminoethoxy vinyl glycine EFE requires 02 and is inhibited under anaerobic conditions. Synthesis of both ACC synthase and EFE is stimulated during ripening, senescence, abscission, following mechanical wounding, and treatment with auxins.

The existence of a closed circulatory system in higher animals provides the organism with an easy and efficient route for the transport of hormones from the site of synthesis to the target tissues. In plants some hormones appear to be transported directly in the vascular tissue for example, cytokinin, GA, and ABA move from the root to the shoot in the xylem GA moves out of young leaves in the phloem and ABA is transported out of wilting leaves in the phloem (Fig. 6.1). However, auxin is not transported directly in the vascular tissue, but instead appears to be transported in cells associated with the phloem (Fig. 6.1). Ethylene poses a special problem in that it is a diffusable gas. However, its precursor, 1-aminocyclopropane-l-carboxylic acid (ACC), is transported from the root to the shoot in the xylem. Therefore, using the traditional concept of a hormone as a translocated chemical messenger, ACC may be more aptly considered to be a hormone than ethylene. 

Studies on the use of the 4-picolyl esters as soluble compounds/ and the applications of 1-aminocyclopropane-l-carboxylic acid in peptide synthesis have appeared. 

Two short reports concerning another mononuclear iron (ferrous) centre, 1-aminocyclopropane- 1-carboxylic acid oxidase, abbreviated ACCO, have been presented. This enzyme catalyses the last step in the synthesis of ethylene, a gaseous hormone involved in ripening of plants. One paper deals with spectroscopic techniques including near infrared (NIR) and circular or magnetic circular dichroism applied to the ferrous active site. The other is on preliminary ENDOR data probing the ligation and structure of this site in the ferric state. ... 

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