2、叔丁氧羰基（Boc） <br/>

      除 Cbz 保护基外，叔丁氧羰基（Boc）也是目前多肽合成中广为采用的{attr}4216{/attr}保护基， 特别是在固相合成中，氨基的保护用 Boc 而多不用 Cbz。Boc 具有以下的于的优点：Boc氨基酸除个别外都能得到结晶；易于酸解除去，但有具有一定的稳定性，Boc-氨基酸能较长期的保存而不分解；酸解时产生的是叔丁基阳离子再分解为异丁烯，它一般不会带 来副反应；对碱水解、肼解和许多亲核试剂稳定；Boc 对催化氢解稳定，但比 Cbz 对酸 要敏感得多。当 Boc 和 Cbz 同时存在时，可以用催化氢解脱去 Cbz，Boc 保持不变，或 用酸解脱去 Boc 而 Cbz 不受影响，因而两者能很好地搭配。 

 2.1、叔丁氧羰基的导入 

       游离氨基在用 NaOH 或 NaHCO3 控制的碱性条件下用二氧六环和水的混合溶剂中 很容易同 Boc2O 反应得到 N-叔丁氧羰基氨基化合物。这是引入 Boc 常用方法之一，它的优点是其副产物无多大干扰并容易除去。有时对一些亲核性较大的胺，一般可在甲 醇中和 Boc 酸酐直接反应即可，无须其他的碱，其处理也方便。 

     对水较为敏感的氨基衍生物，采用 Boc2O/TEA/MeOH or DMF 在 40-50℃下进行较 好，因为这些无水条件下用于保护 O17标记的氨基酸而不会由于与水交换使 O17丢失。有空间位阻的氨基酸而言，用 Boc2O/Me4NOH.5H2O/CH3CN 是十分有利的。 

      芳香胺由于其亲核性较弱，一般反应需要加入催化剂，另外对于伯胺，通过 DMAP 的使用可以上两个 Boc. 

     对于有酚羟基存在的胺，酚羟基上接 Boc 的速度也是相当快的，因而一般没太大的 选择性。

对于有醇羟基存在的，若用 DMAP 做催化剂，时间长了以后醇羟基也能上 Boc， 因此反应尽量不要过夜。

由于氰酸酯的生成，有位阻的胺往往会与 Boc2O 生成脲。

这个问题可通过该胺 NaH 或 NaHMDS 反应，然后再与 Boc2O 反应来加以避免。

      有时在反应中有可能多加了 Boc 酸酐，当分子中无游离酸碱时很难出去，若一定要 除去，一般在体系中加入一些 N,N-二甲基乙二胺或 N,N-二甲基丙二胺，而后将上了 Boc 的 N,N-二甲基乙二胺或 N,N-二甲基丙二胺用稀酸除去。

       由于 Boc 对酸敏感，因此在合成过程中用到酸洗或酸溶解等操作时，为了保险起见， 尽量不用盐酸而用 10%柠檬酸（0.5M）或在低温条件进行。

                                    氨基酸 Boc 保护示例 

      A 4-L, four-necked, round-bottomed flask, equipped with an efficient stirrer, a dropping funnel, reflux condenser, and thermometer is charged with a solution of 44 g (1.1 mol) of sodium hydroxide in 1.1 L of water. Stirring is initiated and 165.2 g (1 mol) of L-phenylalanine is added at ambient temperature, and then diluted with 750 mL of tert-butyl alcohol. To the well-stirred, clear solution is added dropwise within 1 hr, 223 g (1 mol) of di-tert-butyl dicarbonate. A white precipitate appears during addition of the di-tert-butyl dicarbonate. After a short induction period, the temperature rises to about 30–35°C. The reaction is brought to completion by further stirring overnight at room temperature. At this  time, the clear solution will have reached a pH of 7.5–8.5. The reaction mixture is extracted two times with 250 mL of pentane, and the organic phase is extracted three times with 100 mL of saturated aqueous sodium bicarbonate solution. The combined aqueous layers are acidified to pH 1–1.5 by careful addition of a solution of 224 g (1.65 mol) of potassium hydrogen sulfate in 1.5 L of water. The acidification is accompanied by copious evolution of carbon dioxide. The turbid reaction mixture is then extracted with four 400-mL portions of ethyl ether. The combined organic layers are washed two times with 200 mL of water, dried over anhydrous sodium sulfate or magnesium sulfate, and filtered. The solvent is removed under reduced pressure using a rotary evaporator at a bath temperature not exceeding 30°C. The yellowish oil that remains is treated with 150 mL of hexane and allowed to stand overnight. Within 1 day the following portions of hexane are added with stirring to the partially crystallized product: 2 × 50 mL, 4 × 100 mL, and 1 × 200 mL. The solution is placed in a refrigerator overnight; the white precipitate is collected on a Büchner funnel and washed with cold pentane. The solid is dried under reduced pressure at ambient temperature to constant weight to give a first crop. The mother liquor is evaporated to dryness leaving a yellowish oil, which is treated in the same manner as described above, giving a second crop. The total yield of pure white N-tert-butoxycarbonyl-L-phenylalanine is 207–230 g (78–87%), mp 86–88°C, [α]D20 + 25.5° (ethanol c 1.0).  

                                      氨基酸酯 Boc 保护示例 

       A 500-mL, three-necked, round-bottomed flask, is equipped with a magnetic stirring bar, thermometer, reflux condenser protected from moisture by a calcium chloride-filled drying tube, and a pressure-equalizing dropping funnel that is connected to a nitrogen flow line and is charged with a solution of 97% di-tert-butyl dicarbonate (14.3 g, 63.6 mmol) in tetrahydrofuran (100 mL), Methyl serinate hydrochloride (10.0 g, 64.3 mmol) is placed in the flask and suspended in tetrahydrofuran (200 mL) and 99% triethylamine (14.0 g, 138 mmol). The resulting white suspension is cooled with an ice-water bath and the solution of  di-tert-butyl dicarbonate is added dropwise over a period of 1 hr. After 10 min of additional stirring, the ice-water bath is removed and the suspension is stirred overnight (14 hr) at room temperature, then warmed at 50°C for a further 3 hr. The solvent is removed under reduced pressure and the residue is partitioned between diethyl ether (200 mL) and saturated aqueous bicarbonate solution (250 mL). The aqueous phase is extracted with three 150-mL portions of diethyl ether. The combined organic phases are dried with anhydrous sodium sulfate and concentrated under reduced pressure to give 13.4-14.0 g (95-99% crude yield) of N-Boc-L-serine methyl ester as a colorless oil that is used without further purification. [α] D 23 17.0° (MeOH, c 4.41). 

                                       Boc 酸酐在甲醇中与胺直接反应 

       Boc2O (262 g, 1.2 mol) in MeOH (250 ml) was added to a soluton of compound 1 (157.2 g, 1.0 mol) in MeOH (350 ml) at 10°C, and the resulting mixture was stirred at room temperature for 2 h. N1, N1-dimethylethane-1,2-diamine (26 g, 0.3 mol) was added and the mixture was stirred at room temperature for 15 min. The solvent was removed in vacuo, and the residue was dissolved with ethyl acetate (750 ml). The combined organics were washed with 1 N HCl (2 x 250 ml) and brine (2 x 250 ml), dried over sodium sulfate and filtered. The solvent was removed to give compound 2 (250 g, 96%), which was used directly in the next step. 

                                 芳胺的单 Boc 保护示例 

       3- Aminopyridine-2-carboxylic acid (5.02 g, 36 mmol) was suspended in 60 mL of dry DMF, and Et3N (15.2 mL, 108 mmol) was added dropwise at room temperature. To the resulting brown solution was added Boc2O (11.80 g, 54 mmol). After being stirred for 10 min, the 

mixture was heated at 40-50 °C overnight. The reaction mixture was poured into water and was then extracted with EtOAc (2 X 50 mL). The aqueous phase was acidified to pH 4-5 with 2 M aqueous HCl and then extracted with CH2Cl2 (3 X 50 mL). The combined organic phases were then processed in the usual way and chromatographed (13:1 CHCl3/MeOH) to yield the desired product (4.2 g, 49%). 

                                     芳胺的双 Boc 保护示例 

    A solution of NaHMDS (22.0 mL, 22.0 mmol, 1 M in THF) was added to a solution of the amine (2.11 g, 10.0 mmol) and (Boc)2O (5.46 g, 25.0 mmol) in THF (50 mL) at 0°C unde nitrogen. The reaction was allowed to warm to rt and stirred for 16 h. After this time, the reaction was poured into water, extracted into CH2Cl2 (2 X 25 mL), washed with water (2 X 25 mL), dried over Na2SO4, and concentrated to yield a white-yellow solid. Recrystalizat from petroleum ether (40-60 °C) gave the imide as n r ion eedles (3.21 g, 7.80 mmol, 78%). Rf （hexane/ CH2Cl2 1:9, SiO2): 0.10. Mp: 106-109 °C.  

                             酰胺的 Boc 保护示例 

      A 2000-mL, three-necked, round-bottomed flask equipped with an argon inlet adapter, glass stopper, and an overhead mechanical stirrer is charged with a suspension of the hydantoin 1 (26.0 g, 154 mmol) in 1000 mL of 1,2-dimethoxyethane. Triethylamine (15.7 g, 154 mmol) is added in one portion, and the resulting white suspension is stirred for 30 min. Di-tert-butyl dicarbonate (168.0 g, 770 mmol) is then added by pipette, followed by 4-dimethylaminopyridine (DMAP) (0.2 g, 1.5 mmol). Six additional 0.2 g-portions of DMAP are added at 12 hr intervals during the course of the reaction. The reaction mixture is stirred vigorously for a total of 72 hr, and the resulting light yellow solid is then collected in a Büchner funnel using suction filtration. The filtrate is concentrated to a volume of 60 mL by rotary evaporation, and the resulting solution is cooled to 15°C. The precipitate which appears is collected using suction filtration, added to the first crop, and the combined solids are dissolved in 500 mL of chloroform. This solution is washed with three 200-mL portions of 1.0N HCl, and the combined aqueous phases are extracted with 100 mL of chloroform. The combined organic layers are washed with 100 mL of saturated aq NaHCO3 solution and 100 mL of brine, dried over anhydrous MgSO4, filtered, and concentrated by rotary evaporation. The resulting solid is dried at room temperature at 0.01 mm for 24 hr. The resulting finely ground light yellow solid is suspended in 400 mL of diethyl ether in a 1000-mL, round-bottomed flask equipped with a magnetic stirbar, stirred for 2 hr, and filtered on a Büchner funnel washing with four 50-mL portions of diethyl ether. The product is dried under vacuum (85°C; 0.5 mm) for 24 hr to give 60.0–65.3 g (83-90%) of 2 as a ivory-colored solid.  

                                     叠氮还原 Boc 保护示例 

    A 500-mL, single-necked, round-bottomed flask, equipped with a Teflon-coated stirring bar, is charged with a suspension of 0.91 g of 10% palladium on carbon catalyst in 100 mL of ethyl acetate. The flask is connected to a normal pressure hydrogenation apparatus and the catalyst is saturated with hydrogen. After removal of the hydrogen, a solution of 18.2 g (0.0785 mol) of 1 and 20.6 g (0.0942 mol) di-tert-butyl dicarbonate in 80 mL of ethyl acetate is added to the suspension of catalyst, a hydrogen atmosphere reestablished, and the suspension is stirred at room temperature under a slight positive pressure of hydrogen for 4–6 hr, The suspension is filtered through a Celite pad, and the pad is rinsed with several portions of ethyl acetate. The combined ethyl acetate solutions are concentrated on a rotary evaporator and finally under high vacuum to give a pale yellow oil that is initially purified by means of a column packed with silica gel (100 g) using hexane-ethyl acetate (6:1) as eluent. Fractions containing the product are combined and concentrated on a rotary evaporator to give 23.3 g of crude 2 as a colorless oil. The oily crude 2 is dissolved in 70 mL of hexane-ether (3:1), and the solution is cooled to −30°C, seeded, and kept overnight at that temperature (freezer) to allow crystallization. The mother liquor is siphoned out while the mixture is kept at −30°C (dry ice-acetone bath). The crystals are washed with several portions of hexane-ether (3:1) at −30°C, then dried under high vacuum to provide 12.2–12.7 g of diastereomerically and enantiomerically pure diethyl (2S,3R)-2-(N-tert-butoxycarbonyl)amino-3-hydroxysuccinate (2) as colorless prisms, mp 33–34°C;. The combined mother liquor and the hexane–ether (3:1) washings are concentrated on a rotary evaporator to give a colorless oil, which upon crystallization as above provides an additional 2.7–3.8 g of product 2. The combined yield of rystalline 2 is 15.9–16.5 g (66–73%). 

                                          吡咯 Boc 保护示例 

     The solution of 2-bromo-1H-pyrrole (9.8 g, 67.2 mmol) in 40 mL of THF is cooled to −78°C in a dry ice-acetone bath. The flask is equipped with a magnetic stirring bar and a three-way stopcock attached to a balloon filled with nitrogen. To the stirred dark-green solution is added 2.71 g (26.9 mmol) of triethylamine followed immediately by addition of 20.4 g (93.9 mmol) of di-tert-butyl dicarbonate and a catalytic amount (ca. 0.1 g) of 4-dimethylaminopyridine. The flask is evacuated and purged with nitrogen. The mixture is stirred for 8 hr while it is allowed to warm to room temperature. The solvent is removed under reduced pressure at room temperature and 100 mL of hexane is added to the crude product, which is washed with deionized water (3 × 100 mL), dried over sodium sulfate, and concentrated under reduced pressure at room temperature. The crude product is purified by chromatography on amine-treated neutral silica (270 g) using hexane as the eluent. The fractions containing the product are identified by TLC, combined, and concentrated under reduced pressure at room temperature to yield N-tert-Butoxycarbonyl-2-bromopyrrole as a colorless oil (13.5–14.7 g, 82–89%). 

                                          吲哚 Boc 保护示例 

     To a solution of 6-methoxy-3-methylindole (5.0 g, 31 mmol) in distilled acetonitrile (150 mL) were added di-tertbutyl dicarbonate (7.44 g, 34.1 mmol) and DMAP (0.195 g, 1.6 mmol). The reaction mixture was stirred at rt for 12 h. The solvent was removed under reduced pressure. The residue was dissolved in CH2Cl2 (100 mL) and washed with an aqueous solution of 1 N HCl (2 x 50 mL). The aqueous layer was extracted with CH2Cl2 (3 x 30 mL). The combined organic ayers were dried (K2CO3). After removal of solvent under reduced pressure, the sidue was solidified to afford the product (8.12 g, 99%) as a yellow solid: mp 45-46 °C. 

2、2 叔丁氧羰基的脱去 

     Boc 比 Cbz 对酸敏感，酸解产物为异丁烯和 CO2（见下式）。在液相肽的合成中， Boc 的脱除一般可用 TFA 或 50%TFA（TFA:CH Cl = 1:1,v/v）。而在固相肽合成中，由于 TFA 会带来一些副反应（如在得到的胺上上一个三氟乙酰基等）因此多采用 1-2M HCl/有机溶剂。一般而言用 HCl/二氧六环，比较多见。

    用甲醇作溶剂，HCl/EtOAc 的组合使 BDMS 和 TBDPS 酯[1]以及叔丁酯和非酚类 酯在 Boc 脱除时不被断裂，而 S-Boc 除外。但当同时脱除分子中 Boc 和叔丁酯, 或分 子中有游离羧酸基，千万记住不能用 HCl/MeOH,其可将羧酸变为甲酯。同时 AcCl/MeOH，则是一个在甲 中产T 醇 生无水 HCl 的便利方法。这些条件也可用来从羧酸制备酯以及形成胺的盐酸盐。

      在中性的无水条件下 Me SiI 在 CHCl 或 CH CN 中除 了能脱除Boc外，也能断裂氨基甲酸酯、酯、醚和缩酮。通过控制条件可以得到一定的选择性。     当分子中存在一些官能团其可与副产物叔丁基碳正离子在酸性下反应时，需要添加 硫酚( 苯硫酚)来清除叔丁基碳正离子，如此举可防止蛋氨酸和色氨酸的脱 Boc 时的烷 基化。也可使用其它的清除剂，如苯甲醚、苯硫基甲醚、甲苯硫酚、甲苯酚及二甲硫醚。在 Boc 脱去过程中 TBDPS和 TBDMS基对 CF3COOH 是稳定的（在 TBS 存在， 用相对稀一些的 10－20 ％TFA）。伯胺衍生物存在下，ZnBr2/CH2Cl2可以选择性的脱除 仲胺上的 Boc。

                                   TMSOTf 中性条件下脱 Boc 示例 

    To a solution containing 2 (1.0 g, 3.9 mmol) in 30 mL of dry CH2Cl2 was slowly added TBDMSOTf (0.9 mL, 4.1 mmol). After stirring the reaction mixture for 6 h, the solvent was evaporated, and the crude product (0.8 g, 75%) was obtaineded, which was used directly in the next step. 

                      TMSOTf-2,6-lutidine 中性条件下脱 Boc 示例 1 

    To a stirring solution of compound 1 (800 mg, 2.0 mmol) and 2,6-lutidine (0.4463 ml, 4.0 mmol) in CH2Cl2 (6 mL) was added tert-butyldimethylsilyl triflate (0.690 ml, 3.0 mmol) dropwise over 5 min. After 20 min, saturated NH4Cl (10 mL) was added. The mixture w stirred and separated, and the aqueous layer was extracted with Et2O (3 x 15 mL). The combined organic layers were washed with water (2 x 10 mL) and saturated NaCl (10 mL), dried (MgSO4), and concentrated to give the crude silyl carbamate, which was dissolved in THF (10 mL) and cooled to 0°C. A 1.0 M solution of TBAF in THF (2 mL, 2 mmol) added over 5 min, and then the solution was stirred at 0°C for 1 h. The solution was concentrated and chromatographed (95:5 CH2Cl

 as was 2-methanol) through a small plug of silica to ive compound 2 (882 mg, 75%) as a clear oil. 

                           TMSOTf-2,6-lutidine 条件下脱 Boc 示例 

     To a stirred solution of compound l (500 mg, 1.52 mmol) and 2,6-lutidine (0.353 ml, 3.04 mmol) in dry CH2C12 (3.0 mL) at 0 "C was added dropwise t-BuMe2SiOTf (0.523 ml, 2.28 mmol). The reaction mixture was stirred at 0°C for 15 min, quenched with saturated aqueous ammonium chloride solution, and extracted with ether several times. The combined organi phase was washed with H2O and then brine, dried (MgSO4), and concentrated in vacuo to give an oily residue, which upon purification by column chromatography on silica gel (elution with 50% ether in hexane) gave O-silyl ester compound  2 (652 mg, 97%): colorless needles; mp 64.0-65.0°C (hexane).

                                       TFA 脱 Boc 示例 

     To a solution of the β-aminoester (0.2 mmol) in CH2Cl2 (3 mL), cooled to 0°C was added TFA (1mL). After the consumption of the starting material (45 min, monitored by TLC), the mixture was evaporated and then saturated aqueous NaHCO3 was added. The aqueous layer was extracted twice with CH2Cl2 (15 mL), and the organic layer washed with brine and dried over anhydrous Na2SO4. The solvent was removered under vacuum, to afford the amine, which were employed without further purification to prepare the Mosher’s diastereoisomeric amides. 

                                 HCl-Et2O 脱 Boc 示例 

tert-Butyl [1-(tert-butoxycarbonyl)-3-oxo-4-pentenyl]carbamate, 8.73 g (0.0308 mol), is dissolved in 280 mL of an ice-cooled, saturated solution of hydrogen chloride in ether. The solution is kept without stirring at room temperature overnight. The resulting suspension is filtered and the filter cake is immediately washed with dry ether. The washing with ether is repeated four times and, after drying under reduced pressure, 5.48 g (99%) of 4-ketopipecolic acid hydrochloride is obtained as a colorless powder, mp 139–142°C dec. 

                                       HCl-THF 脱 Boc 示例 

     To the Boc protected amine (0.06 g, 0.17 mmol) dissolved in THF (1mL) was added 2M HCl (1mL, 2 mmol) and the mixture stirred 2 h at room temperature. After evaporation of the solvent, the product was extracted into EtOAc (3. 5mL). The organic layer was dried and evaporated under vacuum to afford 17b in 95% yield as a white solid.                                         叔丁酯存在下的脱 Boc 示例 1 

   1.77 ml of Me3SiI are added dropwise at room temperature in the vicinity of 25°C to a soution of 3.8 g of compound 1 in 50 ml of CHCl3. Stirring is contiuned for 30 min, then 20 ml f water are addede. The aqueous phase is separated, then extracted with CHCl3(2 x 20 ml). The organic phases are combined, washed successively with a saturated aqueous Na2CO3(30 ml) and water(2 x 30 ml), then dried over MgSO4 and concentrated to dryness under reduced pressure at 40°C. The mixture of the two diastereoisomers obtained is separated by chromatography on silica (eluent: ethyl acetate/cyclohexane = 1/4). The fractions containing the expected product are combined and concentrated to dryness under reduced pressure at 40°C to give compound 2 (0.5 g), as a yellow-orange oil, used as it is in subsequent syntheses.  

                              叔丁酯存在下的脱 Boc 示例 1 

     To asolution of compound 1 (6.3 g, 21.0 mmol) in ethyl acetate (50 ml) was added 1.1 M HCl in ethyl acetate (28.7 ml, 31.5 mmol). The reaction was stirred at room temperature for 1 h, then washed with water, saturated aq. NaHCO3 and brine. The organic phase was dried (MgSO4), filtered and evaporated to afford compound 2 (3.11 g, 74%) as a yellow oil which crystallized upon standing.  

                            叔丁酯存在下的脱 Boc 示例 3 

     To a solution of compound 1 (149 mg, 0.33 mmol) in CH2Cl2 (2 ml), TFA (1 ml) as added at 0°C and the mixture was stirred for 1 h at 0°C. Saturated aqueous Na2CO3 was added and the mixture was etracted with CHCl3. The etract was purified by silica gel column chromatography to obtained compound 2 (92 mg, 79%).  

                                 吲哚环上 Boc 直接加热脱除示例 

    Compound 1 (62 mg)was heated (neat) at 160-180 °C for 45 min. The residue was purified by flash chromatography (silica gel, CHCl3/MeOH 95/5) to afford Compound 2 (25 mg) as a solid in 50% yield. 11: [R]27D= - 65.9 (c = 0.97, in CHCl3).