MEDCHEM E CHEMBIO Lecture 5 Insects_Pheromones_Chirality

• Insects (Class Insecta)


  • Major group of arthropods
  • Most diverse group of animals on Earth
• Arthropods


  • Characterized by jointed limbs and cuticles mainly made of chitin
  • Cuticle is rigid and replaced periodically by molting
• Chitin


  Long-chain polymer of N-acetylglucosamine
• Chitosan


  Glucosamine that is (partially) deacetylated, more soluble in aqueous media than chitin
• Uses of chitin


  • Used as fertilizer in agriculture
  • Used in industry to thicken and stabilize foods
  • Used in biotechnology for protein purification
• Uses of chitosan


  • Used as biopesticide in agriculture
  • Used in medicine for bandages to reduce bleeding and as an antibacterial agent
  • Used to help deliver drugs through the skin
• Insects are beneficial to the environment and humans in many ways
• Beneficial interactions of insects with humans


  • Pollination of flowering plants
  • Production of useful substances like honey, wax, lacquer and silk
  • Used as human food ("Entomophagy")
  • Scavengers that recycle biological materials
• Insects that transmit diseases to humans

  • Malaria (Anopheles mosquito)
  • Yellow fever (Aedes mosquito)
  • Filariasis (Culex mosquito)
• Many entomologists are involved in pest control, often using insecticides but increasingly relying on bio-control methods
• Insect cells


  • Higher eukaryotic system than yeast, able to carry out more complex post-translational modifications
  • Have the best machinery for folding of mammalian proteins
• Insect antimicrobial peptides are useful in overcoming bacterial drug resistance
• Insect cell cultures are used for production of viral pesticides, vaccines, and basic research
• Bioengineering of insect-derived products like honey, venom, silk, antimicrobial peptides, and anticoagulants into medicines

  
• Pheromones


  Chemical signals with numerous roles like attraction, aggression, aphrodisiacs, anti-aphrodisiacs, kin recognition, and alarm signaling
• Identification of new pheromones

  1. Fractional distillation to separate components

  2. Testing diluted fractions for behavioral responses
• Bombykol


  First identified pheromone, emitted by female silkworm moths to attract males

  
• Pheromones in insects


  • (Z)-9-tricosene (female housefly attractant)
  • (Z)-7-tricosene (anti-aphrodisiac in Drosophila melanogaster)

  
• Pheromones play roles in kin recognition and maintaining social hierarchy in insect colonies

  
• Alarm pheromones can cause dispersal, recruitment, and aggression in insects
• Alarm pheromones


  • (E)-β-farnesene (released by aphids upon predation)
  • Isopentyl acetate (released by stressed honey bees)
• Alarm behaviour


  Flight or fight responses
• Alarm is often confused with attraction or recruitment and can be hard to distinguish in a bioassay
• Alarm pheromones


  • Can cause dispersal of conspecifics and predators or increase recruitment and aggression towards an antagonist
  • Tend to be less specialized than other kinds of pheromones
  • Can serve as general communication cues capable of being received by other species
• Alarm pheromones


  • (E)-β-farnesene
  • Isopentyl acetate
• (E)-β-farnesene


  Released by many aphid species upon predation and signals conspecifics to stop feeding and disperse

  
• Isopentyl acetate


  Released by stressed honey bees
• Smoke, which is used by bee-keepers to calm hives, inhibits receptors involved in the detection of isopentyl acetate
• Parasitic hive beetles are drawn to bee hives


  By bee alarm pheromones

  
• Kodamaea ohmeri yeast, which use the beetles as a vector


  Also produces isopentyl acetate when grown on pollen in hives

  
• Mimicking of the bee alarm pheromones by yeast


  Attracts even more beetles, causing the hive to be overrun with beetles and the bees to abandon the hive

  
• Food-trail pheromones


  Laid down by ant workers as they walk by touching the gaster (the large posterior section of their body) to the floor, inducing other workers to follow it and allowing trunk trails, like motorways, to be laid to new food sources

  
• Mass recruitment


  • A simple process by which workers can be rapidly allocated to a newly discovered food source in order to prevent competitors getting access to it, ensuring that the colony has the monopoly
  • An autocatalytic (self-reinforcing) process governed by positive feedback mechanisms, ensuring a rapid build up of foragers
  • Allows the allocation of foragers to remain dynamic and flexible
• Pheromone molecules


  Generally limited to about 5 to 20 carbons in size
• The complexity of social functions mediated by insect lipid pheromones is matched by the chemical diversity of both volatile and non-volatile signaling signals

  
• Pheromones from diverse chemical classes

  • Hydrocarbons (linear or branched)
  • Fatty acetate esters
  • Alcohols
  • Acid
  • Epoxides
  • Ketones
  • Isoprenoids
  • Triacylglycerides
• Many insect pheromones are derived from the same pool of biochemical precursors such as fatty acids and isoprenes, thus allowing a diversity of chemical structures to be generated by slight modifications to a main backbone

  
• Chirality


  An object that is chiral cannot be superimposed on its mirror image
• Enantiomers


  Pairs of stereoisomers which are mirror images of each other

  
• Diastereomers


  Non-mirror image non-identical stereoisomers