烯丙基作为保护基在修饰寡核苷酸合成中的应用

研究了烯丙基作为核苷糖环羟基保护基在寡核苷酸及其类似物的合成中应用的可能性。烯丙基保护基可用PdCl2在温和条件下脱除,适合应用于对碱不稳定的寡核苷酸的合成。应用烯丙基保护基成功地合成了三胸苷二碳酸酯和二胸苷亚硫酸酯。     

以烯丙基作为核苷中糖羟基保护基的研究

对烯丙基作为核苷糖环上羟基保护基进行了研究.烯丙基可用于核糖羟基的保护,用PdCl₂可脱除核苷糖环上烯丙基,保护及脱保护都很简便.PdCl₂还可脱除核苷糖环5'-OH常用的保护基--对甲氧基三苯甲基及二对甲氧基三苯甲基.控制适当的条件,PdCl₂既能够选择性地脱除对甲氧基三苯甲基或二对甲氧基三苯甲基,又可同时脱除保护糖环羟基的烯丙基.     

一种中性条件下脱除THP保护基的简易方法

四氢吡喃醚(THP)是一种常用的保护基,在有机合成中被广泛地用于羟基的保护。它的脱除通常采用强酸(如三氟乙酸等)条件下进行。近来,曾报道了一些在弱酸性条件下脱除THP保护基的方法。我们利用Me_3SiCl/NaI在中性条件下有效地脱除了THP保护基,见式1。     

烯丙基醚作为保护基团在糖化学中的应用

糖类是多羟基化合物,对于糖类化合物中羟基的保护,可将其制成醚、酯、缩醛或缩酮,对位置合适的多羟基,可将其转化为1,2-或1,3-环醚或环酯。近年来,烯丙基和取代的烯丙基基团在糖化学中作为羟基的保护基团得到广泛的应用。烯丙基作为羟基保护基,最早由Gigg等提出,并由他们首先应用于糖化学的研究。烯丙基醚易于制备,在强碱(如NaOH,NaH)的催化下,羟基化合物与烯丙基溴在苯中回流即可得到很好的产率。烯丙糖苷的制备可通过1.2-缩酮与烯丙醇在氯化氢催化下的反应来实现,如下:     

侧链中含二苯甲酮基的聚硅氧烷的合成与结构表征

在相转移催化剂四乙基溴化铵作用下,利用2,4-二羟基二苯甲酮与烯丙基缩水甘油醚在碱性水溶液中的开环加成反应,合成了中间体4-(β-羟基-γ-烯丙氧)丙氧基-2-羟基二苯甲酮(MUV-0),将其进-步与聚甲基氢硅氧烷进行硅氢化加成反应。合成了侧链中含二苯甲酮基的聚有机硅氧烷。用元素分析、红外光谱、紫外光谱和核磁共振等仪器对中间体以及目标聚硅氧烷的结构进行了表征和测定。结果表明：中间体和聚硅氧烷在紫外光区均具有二苯甲酮衍生物特有的三条吸收谱带,对波长240～400nm的紫外光有良好的吸收作用。     

11α，17-二羟基-及11β，17-二羟基-雄甾-1，4-二烯-3-酮-17腈羟基保护的研究

11α，17-二羟基-及11β，17-二羟基-雄甾-1，4-二烯-3-酮-17腈以乙烯基正 丁醚进行保护，得到双羟基和11-及17-单羟基保护产物，对因保护基引入手性碳而 产生的双羟基保护产物的立体异构体进行了分离纯化和波谱鉴定；单羟基保护产物 的薄层层析和分离中均未能观察到立体异构体的性质差异。     

三甲硅基醚的断裂研究

Sommer等[1]首次应用（Me3SiO）2SO2向醇羟基引人三甲硅基（TMS）以保护羟基以来，已发展出很多方便有效的向醇羟基引人TMS保护基团的方法[2]．通常，立体阻碍越小的醇，其羟基越容易被硅基化，而且该TMS保护基团也就越容易在酸或碱性条件下被水解脱除[2]我们在天然产物PrehisPanolone的合成中[3]，羟基r-丁烯酸内酯2是一个关键的中间体．如何脱除前体三甲硅基醚的r-丁烯酸内酯1中的TMS保护基团是一个关键的问题．我们采用四了基氟化铵（TBAF）[4]（A）、酸性水解[5]（B）、碱性醇解[6]（C）和三氟化硼乙醚溶液（BF3-Et2O）[7]…     

几个类环戊烷抗菌素和茉莉酮及其类似物的新合成——6,6’-二三甲基硅基富烯的合成

本部分工作从研究烯丙基硅烷的氧化反应出发,对α硅基烯丙基自由基的反应性和区域选择性进行了一些探讨,并用这种氧化反应及其产物的一些反应合成了几个天然产物。 在研究烯丙位氧化反应过程中,我们发现在Cu~+催化过氧叔丁醇可将许多烯丙基硅烷氧化成相应的β-硅基α,β不饱和酮。在同类反应中,这个系统被证明是迄今为止氧化能力最强的。从反应所体现的区域选择性可见,硅基可以活化α-C-H键并稳定所生成的α自由基。用烯基硅烷进行同样的反应,由于硅基的活化作用失去,反应性和选择性都大     

RNA化学合成中的保护基

近几年来, RNA的化学合成有了较大进展, 本文讨论了RNA化学合成过程中的保护基问题,着重介绍了核糖核苷的2'-和3'-位羟基的选择性保护方法。     

D-葡萄糖酸衍生物C5和C6羟基保护基迁移现象研究

2-O-甲基-3,4-O-丙酮叉基-D-葡萄糖酸甲酯(6)的C6羟基用乙酰基保护、C5仲羟基用TBS保护得到化合物8,碳酸钾脱除C6-O-乙酰基时,C5-O-TBS迁移到C6羟基得到了化合物9(74%收率),没有得到目标产物12;将化合物6的C6羟基用TBS保护、C5羟基乙酰基保护的化合物10,四丁基氟化铵脱除C6-O...     

A new oligosaccharide synthesis using special hydroxy protecting group

A new hydroxy protecting group for convenient preparation of oligosaccharide was developed using uni-chemo protection (UCP) concept. The UCP group was comprised of polymerized amino acid derivatives and protecting each hydroxyl groups by ester linkage. Depending on the polymerization degree, the hydroxyl groups were characterized and controlled. Using this protecting group, two kinds of sialyl-T analogues were successfully synthesized from same sugar parts merely by repeating Edman degradation and coupling.     

Catalyst‐Directed Diastereo‐ and Site‐Selectivity in Successive Nucleophilic and Electrophilic Allylations of Chiral 1,3‐Diols: Protecting‐Group‐Free Synthesis of Substituted Pyrans

The iridium‐catalyzed, protecting group‐free synthesis of 4‐hydroxy‐2,6‐cis‐ or trans‐pyrans through successive nucleophilic and electrophilic allylations of chiral 1,3‐diols occurs with complete levels of catalyst‐directed diastereoselectivity in the absence of protecting groups, premetallated reagents, or discrete alcohol‐to‐aldehyde redox reactions.     

2‐[Dimethyl(2‐naphthylmethyl)silyl]ethoxy Carbonate (NSEC) as a New Mode of Hydroxyl Group Protection*

2‐[Dimethyl(2‐naphthylmethyl)silyl]ethoxy carbonate (NSEC) is a novel protecting group to mask hydroxyl groups. NSECCl is available in three steps from chlorodimethylvinylsilane and 2‐(bromomethyl)naphthalene. Introduction and removal of the NSEC group are performed easily and rapidly in the presence of most protecting groups currently used in carbohydrate chemistry. The removal of NSEC can be carried out under mild conditions in the presence of various ether and ester protecting groups. Additionally, the NSEC group is stable to glycosylation conditions using glycosyl phosphates. The synthesis of disaccharide 18 containing NSEC has been accomplished.     

Acceleration effect of an allylic hydroxy group on ring-closing enyne metathesis of terminal alkynes: scope, application, and mechanistic insights

An interesting acceleration effect of an allylic hydroxy group on ring-closing enyne metathesis has been found. Ring-closing enyne metathesis of terminal alkynes possessing an allylic hydroxy group proceeded smoothly without the ethylene atmosphere generally necessary to promote the reaction. The synthesis of (+)-isofagomine with the aid of this efficient reaction has been demonstrated. Mechanistic studies of the acceleration effect were also carried out. Results of NMR studies suggested that the reaction proceeded via an "ene-then-yne" pathway. Kinetic studies indicated switching of the rate-determining step as a consequence of the presence of an allylic hydroxy group. These results suggest acceleration of the reentry step of Ru-carbene species by the allylic hydroxy group.     

Directing/protecting groups mediate highly regioselective glycosylation of monoprotected acceptors

A directing/protecting group designed for regioselective functionalization of partially-protected glucopyrannosides has been successfully used to prepare disaccharides in high yields. Most importantly, it has been demonstrated that highly regioselective and stereoselective glycosylation can be achieved when disarmed donors are employed. This study demonstrates the ability of directing/protecting group to induce regioselective glycosylation of carbohydrates and opens the field to the design of other DPGs for other monosaccharides.     

Improved synthesis of the epoxy isoprostane phospholipid PEIPC and its reactivity with amines

An improved synthesis of the naturally occurring hydroxy ketone 1-palmitoyl-2-(5,6)-epoxyisoprostane E 2- sn-glycero-3-phosphocholine (PEIPC) 1, a compound that plays a role in endothelial activation in atherosclerosis, has been carried out using a PMB ether as the key protecting group. Opening of an intermediate with pentylamine shows that the allylic epoxide is the position of attack by nucleophiles.     

Discovery and application of iminotriphenylphosphorane as a formal aromatic primary amine protecting group

During our efforts to selectively synthesise N-arylated benzotriazole fragments, we developed a new primary aromatic amine protecting group strategy showing significant advantages over recognised protecting groups.     

An unusual dehalogenation in the Suzuki coupling of 4-bromopyrrole-2-carboxylates

An unusual dehalogenation of 4-bromopyrrole-2-carboxylates under Suzuki coupling conditions has been observed. This dehalogenation can be suppressed by protection of the pyrrole nitrogen. Using a BOC protecting group, not only is dehalogenation suppressed, but the protecting group is also removed under the reaction conditions.     

Selective deprotection of trityl group on carbohydrate by microflow reaction inhibiting migration of acetyl group

The trityl group is an important and useful protecting group for primary hydroxy groups on carbohydrates. However, during deprotection, neighboring acetyl groups can easily migrate to the deprotected hydroxy groups. Hence, deprotection of trityl groups was optimized using a microreactor with regard to flow rate, reagent concentration, reaction time, and substrate concentration. The optimized microflow reaction conditions inhibited migration and could be applied to large-scale reactions and other substrates.     

Synthesis of photolabile 2-(2-nitrophenyl)propyloxycarbonyl protected amino acids

The 2-(2-nitrophenyl)propyloxycarbonyl (NPPOC) group has been introduced as a photolabile amino protecting group for amino acids to be used as building blocks in photolithographic solid-phase peptide synthesis. NPPOC-protected amino acids were found to be cleaved in the presence of UV light about twice as fast as the corresponding o-nitroveratryloxycarbonyl (NVOC)-protected amino acids.