On the stereochemistry of ethylene biosynthesis

Abstract

The conversion of (i) an equal mixture of the two isomers of cis-2,3-dideuterio-l -aminocyclopropanecarboxylate or (ii) ( &)-trans-2,3-dideuterio-l -aminocyclopropanecarboxylate by apple slices gave in both cases a 1 :I mixture of cis-and trans-I ,2-dideuterioethylene; in contrast the chemical oxidation (NaOCI) of these substances proceeded with complete retention of configuration to cis-dideuterioethylene and trans-dideuterioethylene, respectively.The plant hormone ethylene is derived from methionine via 1aminocyclopropanecarboxylic acid (ACC) (1).lv2 Recently we demonstrated that [2,2,3,3-2H,]ACC (2) was converted by apple slices into C2H,]ethylene without loss of d e ~t e r i u m . ~ Stereospecifically labelled (1) was prepared by bromination (aqueous KBr,, 0 "C, dark) of both transand cis-dideuterio-ethylenes4 to mesoand ( &)-dibromoethylenes, respectively. These were then allowed to react with the lithio-derivative of benzylidene glycine ethyl ester, as shown in Scheme 1, to yield C~~-[~H,]ACC? (3) and (4) {as a 1 : I mixture of l-amino-[~-2,c-3-~H,]-r-l -cyclopropanecarboxylic acid (3) and l-amino-[t-2,t-3-2H2]-r-1 -cyclopropanecarboxylic acid (4) ) and ( *)trans-[2H2]ACC$ (5) {as 1 -amino [2S,3S-2H2]cyclopropanecarboxylic acid (5) and its enantiomer). The stereochemistry of these substances was confirmed by comparison with the computer simulated IH n.m.r. spectra. § These materials were used in the feeding experiments as follows: C~S-[~H~]ACC (3) and (4) (10 mg, 22 rnol % glycine) in water (1.5 ml) was fed to apple slices7 (25 g) at 15 "C in the dark Analysis by 'H n.m.r. (300 MHz) showed that this material contained residual glycine, 6 [D20, sodium 3-(trimethylsi1yl)tetradeuteriopropionate (TSP) = 0.001 3.56(2H, s), (22 mol Yo), and the cis : trans ratio was 99 : 1 . For (3) and (4), 6(D,O, *H decoupled, TSP 0.00) 1.19(2H, s) and 1.34(2H, s).

Formation of cyanide from carbon 1 of 1-aminocyclopropane-1-carboxylic acid during its conversion to ethylene

“…Recently, Pirrung (30) has studied the electrochemical oxidation of ACC, which leads to ethylene formation with loss of stereochemistry, as observed in apple tissue (28). In this model reaction, C-1 of ACC also yields cyanide.…”

The stereochemistry of oxidation of 1-amino-cyclopropanecarboxylic acid

“…4 In contrast, the efficient chemical oxidation of (2) with sodium hypochlorite gave cis-[ 1 ,2-2H2]ethylene with retention of configuration. 3 We have now found that the biosynthetic stereochemical result can be duplicated by oxidation of ACC with various transition metal ions, such as Cu2+, Mn04-, and Fe042-, Table 1. That the amino group is the site of reaction in these processes was indicated by the absence of reaction of ACC in acidic media and further by the observation that whereas cyclopropylamine (lb) gave ethylene (9%) with CuS04, neither the N-ethoxycarbonyl-ACC (4) nor cyclopropanecarboxylic acid produced ethylene when oxidized under the same conditions.…”

The use of stable isotopes in biosynthetic studies

“…245, 246 Mass spectrometry was used by Masamune and co-workers to establish the sequence of production of stress metabolites by tubers of potato (Solanurn t u b e r ~s u r n ) . ~~~ These researchers determined that the laevorotatory isomer of ( f )-[8,8-2H2]solavetivone (232) is converted sequentially into lubimin (233), oxylubimin (234), and finally rishitin (235). The studies by Dewick and co-workers on the biosynthesis of isoflavanoids in red clover (Trifoliurn pratense) provide numerous representative examples of the use of mass spectrometry to study the incorporation of deuteriated advanced precursors.…”

“…This is in accord with the usual retention of up to three hydrogen atoms of acetate in a polyketide starter unit but with the substantial loss of such protons, by exchange, from subsequent units. The mechanism of formation of lubimin (233), hydroxylubimin (234), and rishitin (235) in potato tubers that are infected with Monifinia fructicola (see also Sections 4.2.2 and 4.5.2) was examined, using [2-13C,2H3]a~etate.308 Because of exchange processes that occur during the metabolism of acetate, the proton-decoupled 13C n.m.r. spectra of these compounds display complex upfield multiplets for many of the carbons that have been derived from C-2 of acetate.…”