Xie Xinqiang, Cane David E
Department of Chemistry , Brown University , Box H, Providence , Rhode Island 02912-9108 , United States.
Biochemistry. 2018 Jun 5;57(22):3126-3129. doi: 10.1021/acs.biochem.7b01253. Epub 2018 Jan 5.
Incubation of (±)-2-methyl-3-ketobutyryl-SNAC (3) and (±)-2-methyl-3-ketopentanoyl-SNAC (4) with BonKR2 or OxaKR5, ketoreductase domains from the bongkrekic acid (1) and oxazolomycin (2) polyketide synthases, in the presence of NADPH gave in each case the corresponding (2 R,3 S)-2-methyl-3-hydroxybutyryl-SNAC (5) or (2 R,3 S)-2-methyl-3-hydroxypentanoyl-SNAC (6) products, as established by chiral gas chromatography-mass spectrometry analysis of the derived methyl esters. Identical results were obtained by BonKR2- and OxaKR5-catalyzed reduction of chemoenzymatically prepared (2 R)-2-methyl-3-ketopentanoyl-EryACP6, (2 R)-2-methyl-3-ketobutyryl-BonACP2 (12), and (2 R)-2-methyl-3-ketopentanoyl-BonACP2 (13). The paired dehydratase domains, BonDH2 and OxaDH5, were then shown to catalyze the reversible syn dehydration of (2 R,3 S)-2-methyl-3-hydroxybutyryl-BonACP2 (14) to give the corresponding trisubstituted ( Z)-2-methylbutenoyl-BonACP2 (16).
在NADPH存在的情况下，将(±)-2-甲基-3-氧代丁酰-SNAC(3)和(±)-2-甲基-3-氧代戊酰-SNAC(4)与来自庞贝酸(1)和恶唑霉素(2)聚酮合酶的酮还原酶结构域BonKR2或OxaKR5一起温育，每种情况下均得到相应的(2R,3S)-2-甲基-3-羟基丁酰-SNAC(5)或(2R,3S)-2-甲基-3-羟基戊酰-SNAC(6)产物，这是通过对衍生甲酯的手性气相色谱-质谱分析确定的。通过BonKR2和OxaKR5催化化学酶法制备的(2R)-2-甲基-3-氧代戊酰-EryACP6、(2R)-2-甲基-3-氧代丁酰-BonACP2(12)和(2R)-2-甲基-3-氧代戊酰-BonACP2(13)的还原也得到了相同的结果。然后证明配对的脱水酶结构域BonDH2和OxaDH5催化(2R,3S)-2-甲基-3-羟基丁酰-BonACP2(14)的可逆顺式脱水，生成相应的三取代(Z)-2-甲基丁烯酰-BonACP2(16)。
