Surprising structural lability of a cysteine-S-conjugate precursor of 4-methyl-4-sulfanylpentan-2-one, a varietal aroma in wine of Vitis vinifera L. cv. Sauvignon blanc.
4-Methyl-4-sulfanylpentan-2-one (1; 4MSP) provides a characteristic aroma compound of wines made from Vitis vinifera L. cv. Sauvignon blanc. 4MSP has a strong box-tree odor with a very low perception threshold and is derived from the cysteinylated precursor S-(1,1-dimethyl-3-oxobutyl)cysteine (4; P-4MSP). P-4MSP is transformed into 4MSP during alcoholic fermentation and is an excellent marker of varietal aroma potential. An improved synthesis of P-4MSP as well as of its deuterium-labeled analogue [D(6)]-P-4MSP is described. Several analytical methods (NMR, IR, LSI-MS, GC/MS, ESI-MS(n)) were combined to elucidate spontaneous reversible structural changes of P-4MSP at different pH values. At low pH, P-4MSP has a linear keto form. The keto-enol tautomerism was observed at neutral pH. At pH 8, the formation of N-substituted intramolecular hemiaminal was characterized by ESI-MS and ESI-MS(n) experiments. The hemiaminal loses H(2)O at high pH to produce a cycloimine, which is easily opened by acid hydrolysis. The keto-enol tautomerism explained the incorporation of only six D-atoms during the preparation of the P-4MSP deuterated standard even if [D(10)]mesityl oxide was used. Derivatization conditions for GC/MS analysis strongly affected the ratio of the monosilylated intramolecular cyclic form and the disilylated linear form of P-4MSP. The structural changes of P-4MSP may have a considerable impact on the development of methods of measuring varietal aroma potential.
Shinkaruk
Svitlana
S
ENITA de Bordeaux, 1 cours du Général de Gaulle, CS 40201, F-33175 Gradignan Cedex, France. s-poix-shinkaruk@enitab.fr
Thibon
Cécile
C
Schmitter
Jean-Marie
JM
Babin
Pierre
P
Tominaga
Takatoshi
T
Degueil
Marie
M
Desbat
Bernard
B
Jussier
Christophe
C
Bennetau
Bernard
B
Dubourdieu
Denis
D
Bennetau-Pelissero
Catherine
C
D003500:Cyclization; D003545:Cysteine / Q000737:chemistry; D016208:Databases, Factual; D008401:Gas Chromatography-Mass Spectrometry; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D010422:Pentanones / Q000737:chemistry* / Q000145:classification; D013055:Spectrophotometry, Infrared; D013438:Sulfhydryl Compounds / Q000737:chemistry* / Q000145:classification; D027843:Vitis / Q000737:chemistry*; D014920:Wine
D010422:Pentanones; D013438:Sulfhydryl Compounds; C530764:4-methyl-4-sulfanylpentan-2-one; D003545:Cysteine