L-PAC CAS 1798-60-3(L-Phenylacetylcarbinol), also known as (R)-1-Hydroxy-1-phenylpropan-2-one, is a pivotal chiral pharmaceutical intermediate. It is most renowned as the key precursor in the industrial biosynthesis of L-ephedrine and pseudoephedrine, widely used decongestants and stimulants.
Name :
L-PACCAS No. :
1798-60-3MF :
C₉H₁₀O₂MW :
150.17Purity :
95%Appearance :
Typically a pale yellow to colorless viscous liquid or low-melting solid.Storage Condition :
Should be stored cool, under inert atmosphere, and protected from light.Chemical Properties
Chemical Name: (R)-1-Hydroxy-1-phenylpropan-2-one
IUPAC Name: (1R)-1-Hydroxy-1-phenylpropan-2-one
Synonyms: L-PAC; (R)-PAC; (R)-1-Hydroxy-1-phenyl-2-propanone; L-1-Phenyl-1-hydroxy-2-propanone
CAS Registry Number: 1798-60-3
Molecular Formula: C₉H₁₀O₂
Molecular Weight: 150.17 g/mol
Chemical Structure: It is an α-hydroxy ketone (acyloin) featuring a phenyl group and a chiral center at the benzylic carbon. The natural microbial product is almost exclusively the (R)-enantiomer, which is crucial for its biological activity and downstream utility.
Appearance: Typically a pale yellow to colorless viscous liquid or low-melting solid.
Boiling Point: Decomposes under atmospheric pressure.
Optical Rotation: [α]₂₀ᴰ ≈ -50° to -55° (c=1 in ethanol). This high negative optical rotation is a key identifier for the pure (R)-enantiomer.
Solubility: Soluble in most organic solvents (ethanol, acetone, ethyl acetate, chloroform). Slightly soluble in water.
Stability: The α-hydroxy ketone structure makes it somewhat sensitive. It can decompose upon heating and is susceptible to oxidation and racemization under strong acidic or basic conditions. Should be stored cool, under inert atmosphere, and protected from light.
Biological Activities
Primary Role: L-PAC itself is not a final therapeutic agent. Its primary significance lies in its biological activity as a metabolic intermediate in microbial fermentation.
Biosynthetic Precursor: It is the direct precursor in the microbial pathway for the synthesis of L-ephedrine alkaloids.
Enzymatic Activity: It is produced by the action of pyruvate decarboxylase (PDC), primarily from yeast (e.g., Saccharomyces cerevisiae), on benzaldehyde and pyruvate. This biotransformation is a classic example of a carboligation reaction.
Biosynthesis
L-PAC is almost exclusively produced via microbial biotransformation (fermentation), which is far more efficient and stereoselective than chemical synthesis for this molecule.
1.Microorganism: Bakers' yeast (Saccharomyces cerevisiae) is the most common and historical biocatalyst.
2.Process: In a fed-batch or continuous fermentation, benzaldehyde and a pyruvate source (often pyruvic acid or glucose) are fed to the yeast culture.
3.Key Enzyme: The enzyme Pyruvate Decarboxylase (PDC) catalyzes a two-step reaction: first, decarboxylation of pyruvate to acetaldehyde-thiamine pyrophosphate (TPP) anion; second, carboligation with benzaldehyde to form L-PAC with high enantiomeric excess (>95% (R)).
4.Product Recovery: L-PAC is recovered from the fermentation broth via solvent extraction.
ApplicationsApplications
FAQs
Q1: What is the primary commercial use of L-PAC (CAS 1798-60-3)?
A1: Its exclusive and major industrial use is as the critical biosynthetic precursor in the large-scale fermentation-based production of the decongestants L-ephedrine and pseudoephedrine. Over 80% of the world's pseudoephedrine is manufactured via the L-PAC route.
Q2: Why is the fermentation route preferred over chemical synthesis?
A2: Chemical synthesis of L-PAC typically results in a racemic mixture, requiring costly and inefficient resolution. The yeast biotransformation process is highly stereoselective, producing the desired (R)-enantiomer in high optical purity (>95% ee) in a single, efficient step from cheap starting materials (benzaldehyde and glucose).
Q3: What are the main challenges in L-PAC production?
A3:
Substrate Inhibition/Toxicity: Benzaldehyde is toxic to yeast cells at high concentrations, requiring careful fed-batch control.
By-product Formation: Yeast metabolism can reduce benzaldehyde to benzyl alcohol or reduce L-PAC to phenylpropanediol, reducing yield. Strain engineering and process optimization are used to minimize this.
Product Recovery: Efficient extraction from the aqueous fermentation broth is necessary.
Q4: Can you supply L-PAC, and what specifications are critical?
A4: Yes, it is available from specialized fine chemical and chiral intermediate suppliers. Key specifications include:
Purity (by HPLC/GC, typically >98%)
Enantiomeric Excess (e.e.) (Critical, should be >95% (R))
Optical Rotation (as a key physical constant for identity and purity)
Residual Solvents & Water Content
Q5: Are there any regulatory or safety concerns with L-PAC?
A5: As a direct precursor to pseudoephedrine/ephedrine (which are monitored/controlled substances in many jurisdictions due to potential misuse), the sale and transport of L-PAC are often highly regulated. Suppliers and buyers must comply with strict "know-your-customer" (KYC) procedures, licensing, and regulatory reporting to prevent diversion for illicit drug manufacturing.
Q6: Is there ongoing research to improve L-PAC production?
A6: Yes, significant research focuses on:
Metabolic Engineering: Developing engineered yeast or bacterial strains with higher PDC activity, reduced by-product formation, and greater benzaldehyde tolerance.
Enzyme Engineering: Creating improved PDC variants with broader substrate specificity or higher catalytic efficiency.
Process Intensification: Integrating fermentation with in-situ product removal (ISPR) techniques to overcome inhibition and improve productivity.
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