Solid Phase Peptide Synthesis: t-BOC and Fmoc protocols, resins and cleavage MCQs With Answer

Introduction

This quiz collection focuses on Solid Phase Peptide Synthesis (SPPS) with emphasis on the two dominant protection strategies: t-BOC and Fmoc. It covers resin types and linkers (Wang, Rink amide, Merrifield, 2-chlorotrityl), common coupling reagents, deprotection and cleavage methods, orthogonality of protecting groups, and practical aspects like monitoring, swelling solvents and preventing racemization. Designed for M.Pharm students studying MPC 202T Advanced Organic Chemistry II, these MCQs test conceptual understanding and applied decision-making in peptide assembly and resin cleavage. Use this set to evaluate readiness for lab work, exam preparation and troubleshooting of SPPS workflows.

Q1. What is the primary distinction between t-BOC and Fmoc strategies in SPPS?

• t-BOC uses base-labile N-terminal protection while Fmoc uses acid-labile protection
• t-BOC uses acid-labile N-terminal protection while Fmoc uses base-labile protection
• Both t-BOC and Fmoc are removed under identical conditions
• t-BOC is only used in solution-phase synthesis while Fmoc is for solid-phase

Correct Answer: t-BOC uses acid-labile N-terminal protection while Fmoc uses base-labile protection

Q2. Which reagent is typically used to remove the Fmoc group during SPPS?

• Trifluoroacetic acid (TFA)
• Piperidine in DMF
• Hydrogen fluoride (HF)
• TFA with scavengers such as water and triisopropylsilane

Correct Answer: Piperidine in DMF

Q3. Which resin is most appropriate for synthesizing C-terminal amide peptides?

• Wang resin
• Rink amide resin
• Merrifield resin (chloromethyl polystyrene)
• 2-Chlorotrityl chloride resin

Correct Answer: Rink amide resin

Q4. Which linker/resin provides the mildest acid cleavage conditions, useful for acid-sensitive sequences?

• Wang resin (benzyl ester)
• Rink amide resin (peptide amide linker)
• 2-Chlorotrityl chloride resin
• Merrifield resin

Correct Answer: 2-Chlorotrityl chloride resin

Q5. During t-BOC SPPS, which reagent is commonly used to remove the t-BOC group?

• Piperidine
• Tert-butylamine
• Trifluoroacetic acid (TFA)
• Hydrogen fluoride (HF) or strong acids like TFA for global cleavage

Correct Answer: Trifluoroacetic acid (TFA)

Q6. Which coupling reagent combination is most frequently used to minimize racemization during activation of carboxyl groups?

• DCC alone
• DCC with HOBt or HOAt
• EDC with no additive
• Thionyl chloride activation

Correct Answer: DCC with HOBt or HOAt

Q7. Which scavenger is commonly included during TFA-mediated cleavage to protect carbocations and scavenge reactive species?

• Triethylamine (TEA)
• Triisopropylsilane (TIS)
• Piperidine
• Dimethylformamide (DMF)

Correct Answer: Triisopropylsilane (TIS)

Q8. What is the main safety concern when using anhydrous HF for cleavage in Boc-SPPS?

• HF is a mild irritant with low toxicity
• HF is highly corrosive, extremely toxic and requires specialized equipment
• HF produces CO2 that can over-pressurize reaction vessels
• HF cannot cleave side-chain protecting groups

Correct Answer: HF is highly corrosive, extremely toxic and requires specialized equipment

Q9. The Kaiser test monitors which aspect of SPPS after a coupling step?

• Presence of free amino groups on resin (unreacted amines)
• Extent of resin swelling
• Removal of side-chain protecting groups
• Amount of TFA scavenger left

Correct Answer: Presence of free amino groups on resin (unreacted amines)

Q10. Which side-chain protecting group is commonly used for serine and threonine in Fmoc SPPS?

• Boc (tert-butoxycarbonyl)
• t-Butyl (tBu)
• Trityl (Trt)
• Cbz (carbobenzyloxy)

Correct Answer: t-Butyl (tBu)

Q11. Which of the following statements about orthogonality in SPPS is correct?

• Orthogonality means no protecting groups are used
• Orthogonality refers to protecting groups that can be removed selectively under different conditions
• Orthogonality is only relevant to solution-phase synthesis
• Orthogonality ensures all groups are removed simultaneously

Correct Answer: Orthogonality refers to protecting groups that can be removed selectively under different conditions

Q12. Which resin is derived from chloromethyl polystyrene and historically important for SPPS?

• Rink amide resin
• Wang resin
• Merrifield resin
• 2-Chlorotrityl resin

Correct Answer: Merrifield resin

Q13. Which reagent pair is commonly used in Fmoc SPPS for rapid, low-racemization coupling (popular in automated synthesizers)?

• HATU with DIPEA
• DCC with pyridine
• EDC with HOBt and no base
• SOCl2 activation

Correct Answer: HATU with DIPEA

Q14. What property of the resin is most critical for efficient coupling reactions in SPPS?

• Color of the resin
• Loading capacity irrespective of swelling
• Ability to swell in chosen solvents to allow reagent diffusion
• Melting point of the polymer backbone

Correct Answer: Ability to swell in chosen solvents to allow reagent diffusion

Q15. In Fmoc SPPS, what is the typical cause of incomplete deprotection when using 20% piperidine in DMF?

• Excessive use of coupling reagents
• Insufficient contact time or poor resin swelling
• Use of TFA-sensitive side chains
• Presence of water scavengers

Correct Answer: Insufficient contact time or poor resin swelling

Q16. Which protecting group is commonly used for cysteine in Fmoc chemistry when disulfide formation must be prevented?

• Boc
• Trityl (Trt) or Acm depending on orthogonality
• Fmoc itself
• 2,2,2-Trichloroethyl (TCE)

Correct Answer: Trityl (Trt) or Acm depending on orthogonality

Q17. What advantage does microwave-assisted SPPS provide?

• Increases resin loading permanently
• Speeds up coupling and deprotection steps, often improving yields
• Eliminates need for protecting groups
• Replaces TFA for cleavage

Correct Answer: Speeds up coupling and deprotection steps, often improving yields

Q18. Which cleavage cocktail is typically used to remove peptide from Wang resin and cleave tBu-type side-chain protections?

• Piperidine in DMF
• TFA with scavengers (e.g., TFA/TIS/H2O)
• Hydrogenation over Pd/C
• Anhydrous HF only

Correct Answer: TFA with scavengers (e.g., TFA/TIS/H2O)

Q19. Which analytical method is most commonly used to confirm peptide identity after cleavage from resin?

• Infrared spectroscopy (IR)
• Mass spectrometry (MS), often LC-MS
• Thin-layer chromatography only
• Polarimetry

Correct Answer: Mass spectrometry (MS), often LC-MS

Q20. When synthesizing a peptide with an acid-sensitive side chain, which combination would you choose to protect the N-terminus and enable mild cleavage?

• Use t-BOC strategy with HF cleavage
• Use Fmoc strategy with 2-chlorotrityl resin for mild cleavage
• Use Bzl (benzyl) N-protection with strong acid cleavage
• Avoid any resin and synthesize in solution only

Correct Answer: Use Fmoc strategy with 2-chlorotrityl resin for mild cleavage

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