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201.
用离子色谱法测定面制品和面粉改良剂中的溴酸盐。用30 mL水超声提取样品15 min(脂肪含量高的样品先用正己烷除脂),过HLB柱和银氢柱净化,以AS9–HC色谱柱分离,NaHCO3作为淋洗液,电导检测器检测,实现了复杂基质面制品中溴酸盐的检测。方法线性相关系数大于0.999,最低检测浓度为0.5 mg/kg,加标回收率为78.4%~106.3%。利用建立的方法对面制品和面包改良剂中的溴酸盐进行检测,共检测各类面制品144份,总体合格率为97.2%;检测面包改良剂类产品10份,合格率为40.0%。 相似文献
202.
203.
A robust, practical synthesis of (20S)‐10‐(3‐aminopropyloxy)‐7‐ethylcamptothecin (T‐2513, 5 ), which is a water‐soluble analogue of camptothecin, has been developed. The key step in this synthesis is a highly diastereoselective ethylation at the C20 position by using N‐arylsulfonyl‐(R)‐1,2,3,4‐tetrahydroisoquinoline‐3‐carboxylic acid ester as a chiral auxiliary, which affords the key intermediate ethyl‐(S)‐2‐acyloxy‐2‐(6‐cyano‐5‐oxo‐1,2,3,5‐tetrahydroindolizin‐7‐yl)butanoate ( 8 k ) in 93 % yield and 87 % de. Optically pure compound 8 k was obtained by a single recrystallization from acetone and its further elaboration through Friedlander condensation afforded compound 5 . This synthesis does not require any chromatographic purification steps and can provide compound 5 on a multi‐gram scale in 6.3 % overall yield (16 steps). 相似文献
204.
205.
The introduction of sulfur atoms onto target molecules is an important area in organic synthesis, in particular in the synthesis of pharmaceutical compounds, and a wide variety of sulfuration agents have been developed for thionation reactions over the past few decades. In this Focus Review, we collect and summarize the C? S bond‐formation reactions that have been used to construct C? S bonds in natural products and pharmaceutical compounds. 相似文献
206.
Cope rearrangement is one of the pericyclic reactions in many organic rearrangements. It has high stereoselectivity and has been widely used in organic synthesis chemistry. Herein, the discovery, mechanism, and application of Cope rearrangement were analyzed and discussed. 相似文献
207.
A short and efficient enantioselective synthesis of natural product (S)-3-hydroxypiperidine has been achieved starting from commercially available raw materials employing two catalytic routes: (i) cocatalyzed hydrolytic kinetic resolution (HKR) of racemic methyl-3-(oxiran-2-yl)propanoate; (ii) proline-catalyzed α-aminooxylation followed by Horner–Wardsworth–Emmons olefination in high enantiomeric purity (97% ee) and high overall yield (38%). 相似文献
208.
Stereoselective total synthesis of two chiral lactones, (+)‐trans‐cognac lactone (1b) and (+)‐trans‐aerangis lactone (2c), has been achieved from the same intermediate using a radical‐based cyclization route. 相似文献
209.
Total synthesis of (Z) pulchellalactam, a CD protein tyrosine phosphatase inhibitor, from commercially available methallyl chloride employing ring‐closure metathesis (RCM) as a key step is described. 相似文献
210.
Little is known of the biosynthesis of sesquarterpenes and the synthesis of unnatural terpenoids by sesquarterpene biosynthetic enzymes has not yet been reported. In this study, the enzymatic cyclization of head-to-tail acyclic triterpene β-hexaprene—a natural product isolated from Bacillus clausii—using tetraprenyl-β-curcumene cyclase (TC) from Bacillus subtilis resulted in the formation of two unnatural pentacyclic triterpenes. It was revealed that B. subtilis TC, which forms tetracyclic terpenoid scaffold from tetraprenyl-β-curcumene in vivo, could be used to construct the 6/6/6/6/6-fused pentacyclic scaffold in vitro, suggesting that the active site cavity of TC has sufficient space to accommodate this unnatural pentacyclic scaffold. This is the first report demonstrating the utility of a sesquarterpene cyclase toward the synthesis of unnatural terpenoids. 相似文献