A chain extension method for apocarotenoids; lycopene and lycophyll syntheses

Area of Science:

• Organic Chemistry
• Natural Product Synthesis
• Carotenoid Chemistry

Background:

• Apocarotenoids are valuable natural products with diverse biological activities.
• Efficient synthetic routes are needed for accessing apocarotenoid analogues.
• The Julia-Kocienski olefination is a powerful tool for carbon-carbon bond formation.

Purpose of the Study:

• To develop a novel building block for apocarotenoid synthesis.
• To explore the utility of the Julia-Kocienski olefination in constructing carotenoid backbones.
• To synthesize higher homologues of apocarotenoids (C30 and C40).

Main Methods:

• Synthesis of a C5 benzothiazolyl (BT) sulfone building block with an acetal group.
• Double Julia-Kocienski olefination of the BT-sulfone with C10 2,7-dimethyl-2,4,6-octatrienedial.
• Deprotection of acetal groups to yield C20 crocetin dial.
• Repeated application of olefination and hydrolysis for C30 and C40 apocarotenoid synthesis.

Main Results:

• Efficient synthesis of C20, C30, and C40 apocarotenoid homologues was achieved.
• The Julia-Kocienski olefination proved effective for chain extension.
• Steric hindrance affected the reaction with bulky sulfones, but lycopene and lycophyll were synthesized efficiently.
• Hydroxyl group protection was not required for certain substrates.

Conclusions:

• The developed C5 BT-sulfone is a versatile building block for apocarotenoid synthesis.
• The Julia-Kocienski olefination is a robust method for constructing carotenoid natural products.
• The synthetic strategy allows for controlled chain elongation and access to various apocarotenoid structures.