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Protecting Agents Please inquire for pricing and availability of listed products to our local sales representatives. 1 Protecting Agents Protecting groups are of vital importance in organic synthesis. In ● Acylation Reagents many cases, reaction conditions will effect multiple functionalities, Acyl protecting groups are usually used for the protection of which necessitate the blocking of several functional groups to hydroxy groups and amino groups. Acetyl (Ac), benzoyl (Bz), and afford the correct synthetic transformation. However, protecting pivaloyl (Piv) groups are commonly chosen. Pivaloyl groups is group attachment and removal requires their own conditions as often selected when non-sterically hindered hydroxyl groups well as individual chemical properties, and appropriate selection need to be selectively protected due to the Piv groups large size. of the correct protecting agents is vitally important for synthetic Generally, acyl protecting groups are stable under acidic and strategy. The most useful protecting agents generally need oxidative conditions. Acyl protecting groups are usually several key properties: deprotected under basic or reductive conditions (DIBAL, LAH, - The protecting agents must selectively react with the desired etc.). functional group requiring protection. - The protecting groups must be introduced in high yields O O O without any side reactions. CH3 CH3 - The protected functional groups should be stable under CH3 CH3 various reaction conditions. Ac group Bz group Piv group - The protecting groups must be chemoselectively deprotected O under specific conditions without deprotection of other types X R2 O of protecting groups. R1 OH 1 2 Particularly in total synthesis and for structurally complicated OH or DIBAL R O R compounds, designing the synthetic strategies frequently requires careful selection of protecting groups. Over time, a large array of protection groups have become available due in part to ● Acetalization Reagents, the highly specialized requirements needed in complex synthesis. Thioacetalization Reagents Many of these reagents and protection groups include specialized Acetals and thioacetals are most often used in the protection of conditions for attachment and removal that have high specificity carbonyl groups, particularly that of aldehydes and ketones. The for a given functional and protection group. This brochure acetals and ketals are usually are introduced under acidic introduces a variety of protecting agents, which are sorted based conditions and take advantage of the equilibrium these exist on the methods used for their deprotection. under to install them. Acetals are stable under basic conditions and reductive conditions, and are additionally inert towards nucleophiles and organometallic reagents. Deprotection is ● Silylation Reagents usually carried out via hydrolysis under aqueous acidic conditions. Silyl groups are one of the most commonly used protecting Thioacetals have a wider synthetic resistance and are usually groups to block hydroxy functionalities, as well as for the stable under both acidic and basic aqueous conditions. The protection of carboxyl groups and amino groups. Trimethylsilyl deprotection of thioacetals usually requires the addition of (TMS) and triethylsilyl (TES) are commonly used as general or mercury salts or hypervalent iodine compounds. short-term protecting groups, while triisopropylsilyl (TIPS), tert- butyldimethylsilyl (TBS or TBDMS) and tert-butyldiphenylsilyl R1O OR1 R1S SR1 (TBDPS) groups are used for introducing bulky substituents that R2 R2 R2 R2 are more robust. Silyl protecting groups are often readily acetals or ketals dithioacetals or dithioketals deprotected under acidic conditions, or by fluoride ions. O 2 2 2 R OH R R 2 CH3 C2H5 iPr CH3 Ph R OH O Si CH Si C H Si iPr Si tBu Si tBu 1 3 2 5 R + O H3O 1 CH3 C2H5 iPr CH3 Ph R TMS group TES group TIPS group TBS (TBDMS) group TBDPS group O SH SH 2 X SiR 3 S S R1 R1 OSiR2 R R OH 3 Hg or Ag salts R R F or I2 or (CF3CO2)2IPh 2 Please inquire for pricing and availability of listed products to our local sales representatives. Protecting Agents ● Alkoxymethylation Reagents ● 9-Fluorenylmethyloxycarbonylation Alkoxymethyl groups such as methoxymethyl (MOM) group are (Fmoc) Reagents generally used for the protection of hydroxy groups. They are 9-Fluorenylmethyloxycarbonyl (Fmoc) group is one of the most stable under basic and reducing conditions due to formally being commonly used protecting groups for amino groups in solid acetal functionality. Alkoxymethyl groups are usually deprotected phase peptide synthesis. It is readily deprotected by secondary by acid catalyzed hydrolysis. amines such as piperidine and is stable under acidic conditions. Of note, when a molecule contains both a Fmoc and Boc group, only the Boc group will be selectively removed under acidic conditions. OCH3 OEt OBn O MOM group MEM group BOM group THP group O Cl OCH3 O 1 1 R OH R O OCH3 H or Lewis acid Fmoc group O Fmoc-Cl 1 ● 1 R N O Tritylation (Tr) Reagents R NH2 H Trityl (Tr) groups are mainly used for the protection of hydroxy amine groups. They can selectively protect less sterically-hindered substrates due to their large size. They are relatively stable against bases, oxidizing agents, reducing agents and nucleophiles, and the deprotection is carried out under acidic ● Allyloxycarbonylation (Alloc) Reagents, hydrolysis conditions. Benzyloxycarbonylation (Cbz) Reagents, Benzylation (Bn) Reagents, and Allylation OCH3 (All) Reagents Allyloxycarbonyl (Alloc), benzyloxycarbonyl (Cbz), benzyl (Bn) and allyl (All) groups are commonly used for the protection of amino groups. These protecting groups are generally deprotected OCH3 by palladium catalysts. O OCH3 O Tr group MMTr group DMTr group O O Alloc group Cbz group Bn group Allyl group Tr Cl Alloc-Cl O R1 OH R1 O RNH2 H or RN O Lewis acid cat. Pd or Ni H Hydrides O Cbz-Cl RNH2 RN O cat. Pd or Ni H H2 ● tert-Butoxycarbonylation (Boc) Reagents Bn-X tert-Butoxycarbonyl (Boc) group is one of the most commonly R O R OH used protective groups for amino groups in peptide synthesis. It cat. Pd, H2 is also used for the protection of hydroxy groups. It is stable under basic hydrolysis conditions and catalytic reduction conditions, allyl halide and is inert against various nucleophiles. It is commonly R OH R O base, then H+ deprotected under acidic conditions with trifluoroacetic acid. or cat. Pd, K2CO3 MeOH O CH3 CH3 O CH3 Boc group Boc2O O CH3 CH3 1 R NH2 1 R N O CH3 H H Please inquire for pricing and availability of listed products to our local sales representatives. 3 Protecting Agents ●2,2,2-Trichloroethoxycarbonylation (Troc) ● Photolabile Protecting Reagents Reagents Photolabile protecting groups like D4970 can be introduced to The 2,2,2-trichloroethoxycarbonyl (Troc) group is used as a afford "caged" compounds and is most often employed in protecting group for hydroxy and amino groups. The Troc group is protecting bioactive molecules. The "caging" of bioactive generally deprotected by treatment with zinc powder or by molecule with photolabile protecting groups in particular have electrolysis. proven to be a particularly useful tool in biochemical research. “Caged” compounds are inactivated with photolabile protecting O groups and can be activated by UV or visible light irradiation. Research towards controlling the topical expression of O CCl3 Troc group biomolecule activity using caged compounds has been recently reported and continues to be heavily investigated. To date, Troc-Cl O several classes of caged biomolecule have been synthesized 1 R NH2 1 R N O CCl3 and reported, including: nucleotides, amino acids, biotin, and Zn, H+ H or sugars. electrolysis NEt2 OH bioactive ● 2-(Trimethylsilyl)ethoxycarbonylation substance O h (Teoc) Reagents O O The 2-(trimethylsilyl)ethoxycarbonyl (Teoc) group is used as a Et2N O O protecting group for amines. Teoc groups can be deprotected [D4970] inactive active! with fluoride ion sources such as TBAF. O CH3 CH3 Si O CH3 Teoc group Teoc-Cl O CH3 CH3 References 1 Si R NH2 1 R N O CH3 F H Protective Groups in Organic Synthesis. 5th ed., ed. by T. W. Greene, P. G. M. Wuts, John Wiley & Sons, Inc., New York, 2014. A. Isidro-Llobet, M. Alvarez, F. Albericio, Chem. Rev. 2009, 109, 2455. M. Schelhaas, H. Waldmann, Angew. Chem. Int. Ed. 1996, 35, 2056. ● Sulfonylation Reagents K. Jarowicki, P. Kocienski, Contemp. Org. Synth. 1997, 4, 454. Sulfonyl groups have application as both protecting groups for hydroxy and amino groups, and for the activation of hydroxy functionalities. O O S CH3 S CH3 O O mesyl (Ms) group tosyl (Ts) group O O NO2 S S CF3 O O nosyl (Ns) group trifulyl (Tf) group Ms-Cl O R OH R O S CH3 Na(Hg), isopropanol O or CH3MgBr 4 Please inquire for pricing and availability of listed products to our local sales representatives. Protecting Agents C0306 25mL 100mL 500mL B1087 5mL 25mL 250mL Trimethyl- silylation CH3 CH3 Silylation Reagents CH3 Si Cl CH3 Si Br (TMS) CH3 CH3 Reagents Chlorotrimethylsilane Bromotrimethylsilane CAS RN: 75-77-4 CAS RN: 2857-97-8 I0308 5g 25g T0871 5g 25g 250g T0585 25g 100g T0623 12mL T0801 5g 25g 100g N N CH 3 O CH3 N N CH3 CH3 Si I CF3 S OSi CH3 CH3 Si CH3 CH3 Si CH3 CH3 Si N3 CH CH CH3 O CH3 3 3 CH3 Trimethylsilyl Iodide TMSOTf SIM Trimethylsilyl Azide CAS RN: 16029-98-4 CAS RN: 27607-77-8 CAS RN: 18156-74-6 SIM (in Anhydrous Pyridine） CAS RN: 4648-54-8 T0990 25mL 100mL 500mL B0511 10mL 100mL B0510 12mL B0830 5mL 25mL 100mL B3402 5mL 25mL 100mL CH CH 3 CH3 3 CH3 CH3 Si CH3 CH Si CH CH3 Si CH3 CH3 Si CH3 3 3 CH3 CH3 N N
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