Solid-phase synthesis
Encyclopedia
In chemistry
, solid-phase synthesis is a method in which molecule
s are bound on a bead and synthesized step-by-step in a reactant solution; compared with normal synthesis
in a liquid state, it is easier to remove excess reactant or byproduct from the product. In this method, building blocks are protected at all reactive functional group
s. The two functional groups that are able to participate in the desired reaction between building blocks in the solution and on the bead can be controlled by the order of deprotection. This method is used for the synthesis of peptides, deoxyribonucleic acid (DNA
), and other molecules that need to be synthesized in a certain alignment. More recently, this method has also been used in combinatorial chemistry
.
In the basic method of solid-phase synthesis, building blocks that have two function groups are used. One of the functional groups of the building block is usually protected by a protective group. The starting material is a bead which binds to the building block. At first, this bead is added into the solution of the protected building block and stirred. After the reaction between the bead and the protected building block is completed, the solution is removed and the bead is washed. Then the protecting group is removed and the above steps are repeated. After all steps are finished, the synthesized compound is cut off from the bead.
If a compound containing more than two kinds of building blocks is synthesized, a step is added before the deprotection of the building block bound to the bead; a functional group which is on the bead and did not react with an added building block has to be protected by another protecting group which is not removed at the deprotective condition of the building block. Byproducts which lack the building block of this step only are prevented by this step. In addition, this step makes it easy to purify the synthesized compound after cleavage from the bead.
. Usually, peptide
s are synthesized from the carbonyl group side (C-terminus) to amino group side (N-terminus) of the amino acid
chain in this method, although peptides are synthesised in the opposite direction in cells. In peptide synthesis, an amino-protected amino acid is bound to a solid phase material (most commonly, low cross-linked polystyrene
beads), forming a covalent bond
between the carbonyl group and the resin, most often an amido or an ester
bond. Then the amino group is deprotected and reacted with the carbonyl group of the next amino-protected amino acid. The solid phase now bears a dipeptide. This cycle is repeated to form the desired peptide chain. After all reactions are complete, the synthesized peptide is cleaved from the bead.
The protecting group
s for the amino groups mostly used in the peptide synthesis are 9-fluorenylmethyloxycarbonyl group (Fmoc) and t-butyloxycarbonyl (Boc). The Fmoc group is removed from the amino terminus with base while the Boc group is removed with acid.
Many amino acids bear functional groups in the side chain. In order to prevent these functional groups from reacting with the incoming N-protected amino acids, a number of other protecting group
s specific for the amino acid to be protected is used. In contrast to BOC and Fmoc groups, these have to be stable over the course of peptide synthesis although they are also removed during the final deprotection of peptides.
, RNA
, and modified oligonucleotides are also synthesized by the solid-phase method. Although oligonucleotides can be synthesized in a flask, they are almost always synthesized on solid phase using a DNA/RNA synthesizer. For a more comprehensive review, see oligonucleotide synthesis
.
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
, solid-phase synthesis is a method in which molecule
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
s are bound on a bead and synthesized step-by-step in a reactant solution; compared with normal synthesis
Chemical synthesis
In chemistry, chemical synthesis is purposeful execution of chemical reactions to get a product, or several products. This happens by physical and chemical manipulations usually involving one or more reactions...
in a liquid state, it is easier to remove excess reactant or byproduct from the product. In this method, building blocks are protected at all reactive functional group
Functional group
In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part of...
s. The two functional groups that are able to participate in the desired reaction between building blocks in the solution and on the bead can be controlled by the order of deprotection. This method is used for the synthesis of peptides, deoxyribonucleic acid (DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
), and other molecules that need to be synthesized in a certain alignment. More recently, this method has also been used in combinatorial chemistry
Combinatorial chemistry
Combinatorial chemistry involves the rapid synthesis or the computer simulation of a large number of different but structurally related molecules or materials...
.
In the basic method of solid-phase synthesis, building blocks that have two function groups are used. One of the functional groups of the building block is usually protected by a protective group. The starting material is a bead which binds to the building block. At first, this bead is added into the solution of the protected building block and stirred. After the reaction between the bead and the protected building block is completed, the solution is removed and the bead is washed. Then the protecting group is removed and the above steps are repeated. After all steps are finished, the synthesized compound is cut off from the bead.
If a compound containing more than two kinds of building blocks is synthesized, a step is added before the deprotection of the building block bound to the bead; a functional group which is on the bead and did not react with an added building block has to be protected by another protecting group which is not removed at the deprotective condition of the building block. Byproducts which lack the building block of this step only are prevented by this step. In addition, this step makes it easy to purify the synthesized compound after cleavage from the bead.
Solid-phase synthesis of peptides
Solid-phase synthesis is the most common technique for peptide synthesisPeptide synthesis
In organic chemistry, peptide synthesis is the production of peptides, which are organic compounds in which multiple amino acids are linked via amide bonds which are also known as peptide bonds...
. Usually, peptide
Peptide
Peptides are short polymers of amino acid monomers linked by peptide bonds. They are distinguished from proteins on the basis of size, typically containing less than 50 monomer units. The shortest peptides are dipeptides, consisting of two amino acids joined by a single peptide bond...
s are synthesized from the carbonyl group side (C-terminus) to amino group side (N-terminus) of the amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
chain in this method, although peptides are synthesised in the opposite direction in cells. In peptide synthesis, an amino-protected amino acid is bound to a solid phase material (most commonly, low cross-linked polystyrene
Polystyrene
Polystyrene ) also known as Thermocole, abbreviated following ISO Standard PS, is an aromatic polymer made from the monomer styrene, a liquid hydrocarbon that is manufactured from petroleum by the chemical industry...
beads), forming a covalent bond
Covalent bond
A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding....
between the carbonyl group and the resin, most often an amido or an ester
Ester
Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
bond. Then the amino group is deprotected and reacted with the carbonyl group of the next amino-protected amino acid. The solid phase now bears a dipeptide. This cycle is repeated to form the desired peptide chain. After all reactions are complete, the synthesized peptide is cleaved from the bead.
The protecting group
Protecting group
A protecting group or protective group is introduced into a molecule by chemical modification of a functional group in order to obtain chemoselectivity in a subsequent chemical reaction...
s for the amino groups mostly used in the peptide synthesis are 9-fluorenylmethyloxycarbonyl group (Fmoc) and t-butyloxycarbonyl (Boc). The Fmoc group is removed from the amino terminus with base while the Boc group is removed with acid.
Many amino acids bear functional groups in the side chain. In order to prevent these functional groups from reacting with the incoming N-protected amino acids, a number of other protecting group
Protecting group
A protecting group or protective group is introduced into a molecule by chemical modification of a functional group in order to obtain chemoselectivity in a subsequent chemical reaction...
s specific for the amino acid to be protected is used. In contrast to BOC and Fmoc groups, these have to be stable over the course of peptide synthesis although they are also removed during the final deprotection of peptides.
Solid-phase synthesis of DNA and RNA
Relatively short fragments of DNADNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
, RNA
RNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
, and modified oligonucleotides are also synthesized by the solid-phase method. Although oligonucleotides can be synthesized in a flask, they are almost always synthesized on solid phase using a DNA/RNA synthesizer. For a more comprehensive review, see oligonucleotide synthesis
Oligonucleotide synthesis
Oligonucleotide synthesis is the chemical synthesis of relatively short fragments of nucleic acids with defined chemical structure . The technique is extremely useful in current laboratory practice because it provides a rapid and inexpensive access to custom-made oligonucleotides of the desired...
.
Applications
- Solid phase synthesis was used to synthesise N-(pyrimidin-2-yl)amino acid amides starting from a Rink resin in drugs research.
- Noncovalent solid-phase organic synthesisNoncovalent solid-phase organic synthesisNoncovalent solid-phase organic synthesis or NC-SPOS is a form of Solid-phase synthesis whereby the organic substrate is bonded to the solid phase not by a covalent bond but by other chemical interactions. This bond may consist of an induced dipole interaction between a hydrophobic matrix and a...