保护基

The seal coating can improve the airtightness of the coatings and prevent the corrosive gas penetrating into the base metal.

结果表明，3种涂层都可以起到保护基体，减缓腐蚀的作用。

Constituting dicycle; 2. region selectively reducing six-membered ring ketocarbonyl radical; 3. introducing 7alpha-hydroxy group; 4. Aldol reaction to introduce side chain and obtain 8alpha-hydroxy group; 5. oxidizing the position 7 hydroxy group into ketone; 6. turning the configuration of the position 7 hydroxy group; 7. glycosidating the position 7 hydroxy group; and 8. eliminating protecting group to obtain the target compound.

该方法包括如下步骤：(1)双环的构建；(2)区域选择性还原六元环酮羰基；(3)7α-羟基的引入；(4)Aldol反应引入侧链，同时得到8α-羟基；(5)7位羟基氧化为酮；(6)7位羟基构型的翻转；(7)7位羟基的糖苷化；(8)脱除保护基得到目标化合物。

Started from D-tyrosine, we obtained the tetramic acid 96 using Jouin reaction. The assembly of the second fragment 109 was stared from 1,4-butandiol,using asymmetric alkylation reaction developed by Oppolzer as a key step. Coupling of the tetramic acid 96 with 109 provided the key intermediate 110 according to Yoshii\'s procedure. After remove protective group and Sharpless epoxidation, we obtained the key intermediate 113. Its macrocyclization to form the final product is in progress.

本论文的第二章主要对Macrocidin A开展了合成工作，我们从D构型的酪氨酸出发，经过官能团转换；利用Jouin反应生成Tetramic acid 96，另外一个片断从1，4-丁二醇开始经过多步反应生成碘化物104，利用Oppolzer发展的手性樟脑磺酰胺为辅基参与的不对称烷基化反应，引入手性甲基，生成关键中间体109，接着通过Yoshii发展的方法连接96和109生成110，经过Sharpless不对称环氧化反应建立环氧化合物，然后脱去保护基得到关环前体113，分子内的Mitsunobu反应进行关大环反应正在进行之中。

Traditiona- ly, the buccolingual width of the pontic is reduced in clini- cal practice to lessen the load of the abutment teeth. But it has little scientific basis.

为了保护基牙、减少基牙的负荷，临床上常常采用减小桥体〓面颊舌径宽度的方法，但是对此一直未有科学的依据，对桥体〓面的设计还缺乏统一的认识。

A with under strong base butyl Lithium, Wittig reaction was carried out, after cast off extremital 2,3-dihydropyran which protected hydroxy group, then 5,14-gadoleyl-1-ol was obtained.

a与在强碱正丁基锂的作用下进行Wittig反应，然后脱去末端的2，3-二氢吡喃保护基，得到5， 14-二十碳二烯醇。

A new phenomenon that ketal can be deprotected by strong base NaH wasfound.

在实验过程中首次发现在强碱氢化钠作用下，缩酮结构能脱去保护基而复原为酮基这一现象。

Approaches of increasing wearability of materials under sand slurry wear condition were to reduce the micro-cutting of matrix structure and cut down the desquamating of carbide particles.

提出了在泥沙磨损条件下提高材料耐磨性的途径：一方面是如何减少基体组织的显微切削磨损；另一方面是如何使碳化物不易脱落，更好地起到保护基体的作用。

Reaction of L-tyrosine with benzyl bromide in the presence of copper sulfate led to the protection of phenol group on the side chain of L-tyrosine to give H-Tyr-OH in 45% yield via a copper complex intermediate.

酪氨酸与溴化苄在硫酸铜存在下反应，选择性地在其侧链酚羟基上引入苄基保护基，通过反应条件的优化，反应产率达到45%。

How to select the abutments properly and how to protect the abutments are critical to the design of a fixed bridge.

因此如何正确合理地选择基牙、如何保护基牙的健康是固定桥设计的关键。

A fragment of a lozenge-shaped pattern sword is examined and analyzed. It is found that the sword was cast with bronze alloy. There was a thin fine dendrite layer in some areas of the fragment surface. Its structure and compositions are different from the matrix in this fragment.

本文对东周时期一块菱形纹饰剑残段进行了分析测试，结果表明：在剑的表面规则地分布着一层厚约几十μm的细枝晶层，该层的成分和组织与基体完全不同，有较好的耐蚀性，能保护基体不受腐蚀。

In the United States, chronic alcoholism and hepatitis C are the most common ones.

在美国，慢性酒精中毒，肝炎是最常见的。

If you have any questions, you can contact me anytime.

如果有任何问题，你可以随时联系我。