the APIC 3rd Party Audit Task Force on behalf of the Active Pharmaceutical Ingredient Auditing of registered starting material (RSM) suppliers is a primary activity Instructions for the protection of clean equipment from contamination prior. The production of quality starting materials must be carefully planned in order to practices (GMP) guidelines published by WHO2 or under development3. the dosage form and the starting materials and are often intended to protect them. Control of starting materials and intermediate, bulk and finished products manufacture or environmental protection: these are normally governed by national.
Material Starting 3. Protect
An internal benchmarking exercise was undertaken with careful consideration of recent health authority feedback. The benchmarking results were used to build and test a risk assessment tool.
The specific criterial for the tool and the algorithm are contained in Table 1. From the synthetic scheme values for each of the criteria can be counted and the algorithm used to calculate a risk score.
The overall risk score is built up from individual risks each contributing to the total. Proximity and purging power were captured as stages and steps respectively where a minimum of 4 bond-making stages and 8 impurity purging steps were considered low risk. Impurity carryover and stability were considered individually as binary risks 0 is low, 1 contributes to overall risk.
The risk assessment tool was applied to starting materials for processes with recent submissions for which significant health authority queries had been received and to some development projects where the starting materials were identified as high risk during internal project review. These queries correlated well with high overall risk scores as illustrated by the following examples.
Demonstration of the Risk Assessment Tool: To demonstrate the risk assessment tool the synthesis scheme for Vemurafenib shown in Figure 1 Patent submitted in 9 was assessed. The results are shown in Table 2.
In this demonstration no starting materials were identified as high risk by the risk assessment tool primarily and the starting materials were globally accepted health authorities.
In the example shown in Table 3 Starting Material 3 was identified as high risk by health authorities. Unfortunately, our editorial approach may not be able to accommodate all contributions. Our editors will review what you've submitted, and if it meets our criteria, we'll add it to the article. Please note that our editors may make some formatting changes or correct spelling or grammatical errors, and may also contact you if any clarifications are needed.
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For the manipulation of functional groups and formation of new covalent bonds we make use of a large number of Reagents and Name Reactions. In complex organic syntheses, the starting materials and intermediates in the synthetic scheme often have more than one reactive functional group. A few such multifunctional building blocks are shown below to illustrate this point Fig 4. While working on such complex.
We would discuss some of the important protecting groups in this chapter. Before proceed further, it must be emphasized here that this protocol should be applied only after alternate options have been critically analyzed.
In large-scale reactions, this leads to a huge impact to the Atom Economy and pollution cost of the synthetic process. All this translates into an increase in the overall cost of the final drug molecule.
By choosing an appropriate selective reagent to suit the scheme on hand, you could selectively attack only one of the reactive sites. Consider an olefinic ketone Fig 4. Sodium borohydride reduction in methanol as solvent could selectively reduce the keto- group to a secondary alcohol. On the other hand, diborane reagent in THF as solvent would be a reagent of choice when the selective reduction at the olefin moiety is desired.
Diborane reduction of an olefin is several times faster than reduction of ketones. The oxidative cleavage of borane product is also selective. In C — C bond formation reactions we come across several such site-selective reagents. One such reagent widely used in research is the Wittig reagent. They attack the aldehyde or ketone selectively in the presence of ester, nitrile. In the case of a molecule like 4. Both the functional groups could react with a Grignard Reagent.
Carboxylic acid group would first react with one mole of the Grignard Reagent to give a carboxylate anion salt. This anion does not react any further with the reagent. When two moles of Grignard Reagent are added to the reaction mixture, the second mole attacks the ketone to give a tertiary alcohol. On aqueous work-up, the acid group is regenerated.
Thus, the first mole of the reagent provides a selective transient protection for the —COOH group. Once the acid group is esterified, such selectivity towards this reagent is lost. The reagent attacks at both sites. If reaction is desired only at the ester site, the keto- group should be selectively protected as an acetal.
In the next step, the grignard reaction is carried out. Now the reagent has only one group available for reaction. On treatment with acid, the ketal protection in the intermediate compound is also hydrolyzed to regenerated the keto- group. This technique is best illustrated with peptide bond formation and associated deprotection reactions. When two amino acids A and B react under conditions for the peptide bond condensation reaction, a mixture of 4 dipeptides at least could be formed as shown below.
If we are interested in only one product A — B, we have to do selective protections and selective deprotections in a proper sequence. Consider the following peptide bond formation reaction. Let us look closely at two different dipeptide formation schemes.
In the following sequence, the C — terminal is protected in two different ways for one amino acid. For the second amino acid, the N — terminal is protected with an acid labile Boc- protection.
In the next step, the two monoprotected amino acids are coupled as shown below. Take a close look at both the products. In the first product, both protections are acid sensitive. If the final product desired is the protection-free dipeptide, this is indeed a short route. If the desired product is a mono-protected dipeptide, then selective deprotection is the preferred reaction. This is feasible only when we use starting compounds that are differentially protected.
This is called Orthogonal Protection. Similar techniques are available for other functional groups as well. In the introduction, we have seen that carboxylate ion lends protection to an attack of Grignard reagents at this carbonyl carbon.
However, this is not sufficient for a vast variety of reagents. The use of this group as protection for —COOH group is rare. The most common protection groups are esters of methanol, ethanol and t-butanol Fig 4.
Methyl esters are readily prepared by two procedures. The diazomethane procedure is suitable for methyl esters small scale only. The alcohol esterification procedure is common for all alcohols except tert-butanol. Note that only t-butyl esters proceed through the O — alkyl fission mechanism.
All other esters proceed via O — acyl fission mechanism. The t-butyl group being bulky, the acyl carbonyl is shielded from nucleophilic attacks. This is of great value in peptide synthesis. Also note that the benzyl esters are labile with base catalysed hydrolysis as well as hydrogenolysis which is another fission involving the ether oxygen bond. In this discussion let us focus on the classes of protecting groups rather than an exhaustive treatment of all the protections.
There are two general methods for the introduction of this protection. Transketalation is the method of choice when acetals ketals with methanol are desired. Acetone is the by-product, which has to be removed to shift the equilibrium to the right hand side. This is achieved by refluxing with a large excess of the acetonide reagent. Acetone formed is constantly distilled. In the case of cyclic diols, the water formed is continuously removed using a Dean-Stork condenser Fig 4.
The rate of formation of ketals from ketones and 1,2-ethanediol ethylene glycol , 1,3-propanediol and 2,2-dimethyl-1,3-propanediol are different. So is the deketalation reaction. This has enabled chemists to selectively work at one center.
The following examples from steroid chemistry illustrate these points Fig 4. The demand for Green Chemistry processes has prompted search for new green procedures. Some examples from recent literature are given here Fig 4. Compared with their oxygen analogues, thioketals markedly differ in their chemistry. The formation as well as deprotection is promoted by suitable Lewis acids. The thioacetals are markedly stable under deketalation conditions, thus paving way for selective operations at two different centers.
When conjugated ketones are involved, the ketal formation as well as deprotection proceeds with double bond migration. On the other hand, thioketals are formed and deketalated without double bond migration Fig 4. These are the classical protecting groups for primary and secondary amines. The reagents are cheap and the protocol is simple.
Such amides generally need drastic conditions for deprotection, though the yields are generally good Fig 4. A standard procedure is refluxing in aqueous alkali or aqueous mineral acid.
Due to the drastic conditions, care should be exercised in this procedure to ensure racemi zation is avoided. Amides are generally crystalline solids that are easily purified by crystallization. When the protection is introduced at the early stages of a long synthetic scheme and a very stable protection is desired as in nucleotide synthesis an amide is the most preferred protection. Several more labile amide bonds have been investigated.
The amides of trifluoroacetic acid are of special interest. N — Phthaloyl Protection N — Pht. When the reaction center is part of the asymmetric center as is the case in amino acids racemization is often observed. Classical deprotection procedure using hydrazine is however very easy and mild, provided a competing reactive center such as ester is absent Fig 4.
Another useful deprotection procedure is reduction using sodium borohydride, which selectively reduces one of the carbonyl groups. The reaction conditions are sufficiently basic to remove the proton from the newly formed —OH and complete the cleavage as shown in the mechanism below Fig 4.
N — Carboxylic acid Esters as protective groups. As described above, the amide bonds are very strong. On the other hand, the ester bonds are easily cleaved by mild base conditions. A carboethoxy protection on amine has an amide bond as well as an ester bond. Since N — COOH groups obtained on hydrolysis are very unstable, this protection provides a large family of protective groups for primary and secondary amines.
These groups are easily introduced using the corresponding chloroformate esters. Anhydrides or mixed anhydrides under mild basic conditions.
Both these protections could be removed under prolonged stirring with base at room temperature. Though mild, some racemisation is sometimes observed. The N — Cbz protection has an added advantage in that it could be easily cleaved under hydrogenolysis conditions Fig 4.
N — Cbz Protection is however stable to acidic conditions. Compare this with —Boc protection discussed below. The Tert-Butyloxycarbonyl Protection could be introduced and removed under very mild acid conditions.
This protection is stable to alkali and hydrogenolysis Fig 4. Thus, N — Z and N — Boc are complimentary as protective groups. N — Fluoromethyleneoxycarbonyl Protection Fmoc. Protection as well as deprotection steps proceed under mild conditions in good yields Fig 4. The mechanism for Fmoc deprotection is shown in Fig 4. Silylation is a common protection for active hydrogen on heteroatoms.
In the case of N — Si bond, quaternary ammonium fluorides cleave this bond Fig 4. This protection is very stable. N — Tosylation is easily carried out through acid chloride procedure. It is cleaved by solvated electron cleavage reaction. When this group is attached to a primary amine, the —NH group becomes very acidic Fig 4. Acetates — Ac and benzoates — Obz: The — OH group protection chemistry has been extensively investigated.
Records of Raw Materials, Intermediates, API Labelling and Packaging Materials. manufacture, nor aspects of protection of the environment. . 3. Reviewing all production batch records and ensuring that these are completed and signed. 3. Quality Assurance. 4. Personnel and Education. 5. Buildings and Facilities quality of starting materials of herbal origin requires an adequate quality . Buildings must provide adequate protection for the harvested medicinal plants/ herbal. To protect patients from potential unknown impurities introduced prior to The high risk score of Starting Material 3 correlates with the health.