Methionyl acetate

Methionine can be obtained from enzymatic protein hydrolysates or from petrochemical sources. To a lesser extent than cysteine, it is a raw material in Maillard reactions for the preparation of process flavours and it can also be utilised as a precursor for the chemical preparation of the sulfide methional, which is an important flavour constituent for potato, malt, seafood and many other flavours. Methional can be reduced to methionol, which can be esterified with organic acids to, for instance, methionyl acetate and methionyl butyrate, which are useful compounds for pineapple and other fruit flavours (Scheme 13.16). 

The production of the higher alcohols, the acetates of isoamyl alcohol and phenylethyl alcohol, and the ethyl esters of the C6-C10 fatty acids has been studied in semiaerobic sugar fermentations by strains of . cerevisiae and S. uvarum. S. cerevisiae generally produced more esters than S. uvarum. Isoamyl acetate was the main ester produced by >. cerevisiae. and others, in decreasing order, were ethyl caprylate, ethyl caproate, ethyl caprate and phenylethyl acetate(39). Several unusual thio compounds have been produced by Saccharomvces in model anaerobic fermentations using amino acids such as methionine as the sole carbon source(21). These model fermentations produce methylthiopropanal and traces of other sulfur containing compounds, such as methionyl acetate and 2-methyltetrahydrothiophene-3-one. 

Analysis of Methionyl Acetate in Canary Melon Using Stable Isotope Dilution Analysis... 

Stable isotope dilution analysis was used to determine the amount of 3-methylthiopropyl acetate (methionyl acetate) in the fruit of a ripe canary melon. A deuterium-labeled standard was prepared from 3-methylthiopropan-l-ol and acetic anhydride-dg using standard organic synthesis practices, and it was distilled... 

One of the benefits of stable isotope dilution analysis is shown in Fig. 9. The 100-g sample prepared above was kept in a refrigerator and analyzed repeatedly over a period of 6 hours. During that time both the methionyl acetate from the melon and the deuterated methionyl acetate standard decreased in concentration due to degradation reactions, presumably through enzymatic action. Despite a reduction of over 70% in the total GC/MS peak area, the calculated concentration remained constant at a value of 3.99 0.07 ppm. 

Figure 9 Graph showing the decrease in peak area (circles) of methionyl acetate isolated from a Canary melon puree by headspace SPME versus the amount calculated (triangles) using stable isotope dilution analysis. A 100-g sample of the puree was spiked with 100 Xg of deuterated methionyl acetate and 5-g samples were removed from refrigeration at regular intervals for SPME GC/MS analysis. The mean of the calculated amount was 3.99 0.07 xg/g.

A solution of 3.55 parts of L-trypTtophanyl-L-methionyl-L-aspartyl-L-phenylalanine amide trifluoroacetate in 30 parts of dimethylformamide is cooled to 0 C, and 1.01 parts of tri-ethylamine are added. The mixture is stirred while 1.84 parts of N-tert-butyloxycarbonyl-(3-alanine 2,4,5-trichlorophenyl ester are added at 0 C. The reaction mixture is kept at 0°C for 48 hours and then at 20°-23°C for 24 hours. The mixture is added to a mixture of 100 parts of ice-water, 0.37 part of concentrated hydrochloric acid (SG 1.18), 1.2 parts of acetic acid and 20 parts of ethyl acetate. The mixture is stirred for 15 minutes at 0°-10°C and is then filtered. The solid residue is washed with water and then with ethyl acetate, and is dried at 40°-50°C under reduced pressure. There is thus obtained N-tert-butyloxycarbonyl-)3-alanyl-L-tryptophanyl-L-methionyl-L-aspartyl-L-phenylalanine amide, MP 213°C with decomposition. 

Reagents reactive solely toward the methionyl side-chain in native proteins have not been described to date. Selective conversion of the thioether to the sulfoxide derivative by photosensitized oxidation has been reported in a protein devoid of free thiol groups. The selective photosensitized oxidation employed methylene blue or hema-toporphyrin as sensitizers, and aqueous acetic acid (30-90% v/v), or acidic buffers at pH 2-6.5, as solvents (Scoffone et al. 1970). Anaerobic photo-oxidation in 4 M aqueous acetone has been reported to lead to the same result (Gennari and Jori 1970). Methionine can be regenerated from the sulfoxide by incubation with thiols (5 % aqueous j9-mercapto-ethanol at pH 8.0, for 24 hr under Nj Jori et al. 1968). 

Fig. 5. The effect of eRF on the formation of methionyl-puromycin. The indicated amounts of eIF-2 were added to 25 /al incubation mixtures which contained in addition to those mentioned in the legend to Fig. 4 10 pmole of 80 S ribosomes (instead of 40 S) and 10 pmole PH]Met-tRNA, 1 mM puromycin (HCl)j, 10 pmole eIF-3, 10 pmole eIF-4C, 4 pmole eIF-4D, and 3 pmole eIF-5. Samples were incubated at 37°C for 60 minutes, followed by extraction with ethyl acetate according to Leder and Bursztyn (14).

MS, MS/MS and MS experiments were performed with a LTQ-Orbitrap (Thermo Fisher Scientific Inc., San Jose, CA, USA) mass spectrometer equipped with a Triversa Nanomate (Advion Biosciences Inc., Ithaca, NY, USA). Compound solutions were infused with a nanospray chip. The mass spectrometer was first calibrated externally with a mixture containing caffeine, L-methionyl-arginyl-phenylalanyl-alanine (MRFA) and Ultramark 1621 in ACN, MeOH, HjO, acetic acid. Sub-ppm mass accuracy was finally achieved using an internal calibration (lock mass) in both MS and MS/MS mode. The resolution of Orbitrap MS was set to 100,000 (FWHM) at m/z 400. Electrospray ionization (ESI) was used. For MS/MS experiments, an isolation width of 1.5 Da was used. The normalized collision energy was set to the value when the precursor ion was exhausted. Helium was used as the collision gas. 

Retinoids failed to activate NADPH oxidase in dibutyryl cAMP differentiated HL-60 cells (Seifert and SCHACHTELE 1988). In HL-60 cells retinoids have been found to potentiate formyl-methionyl-leucyl-phenylalanine-induced and phorbol myrist-ate acetate-induced 02 formation (Seifert and SchAchtele 1988). Using receptor specific retinoid analogues it was demonstrated that retinoid X receptor-retinoic acid receptor heterodimers mediate retinoid-induced differentiation of HL60 cells, while retinoid X receptor-retinoid X receptor homodimers mediate subsequent retinoid-mediated apoptosis (Nagy et al. 1995, Kizaki et al. 1996). 

Alexandrova and Smrt (68) described the synthesis of cytidylyl- (3 to5")-2"-0-methyl-adenosine 3 -0 (and 2 -0)- -formyl-L-methionyl derivatives with obtained using Silufol UV254 silica gel sheets in chloroform-methanol (8 2), chlorform-methanol (95 5), 1-butanol-acetic acid-H20 (5 2 3), chloroform-methanol (9 1) and 2-propanol-conc., in aqueous ammonia-H20 (7 1 2). 

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