lactone, any of a class of cyclic organic esters, usually formed by reaction of a carboxylic acid group with a hydroxyl group or halogen atom present in the same molecule. Commercially important lactones include diketene and β-propanolactone used in the synthesis of acetoacetic acid derivatives and β-substituted propanoic (propionic) acids, respectively; the perfume ingredients pentadecanolide and ambrettolide; vitamin C; and the antibiotics methymycin, erythromycin, and carbomycin.

The γ- and δ-lactones, containing five- and six-membered rings, respectively, are the most common. They are formed by loss of water from the corresponding hydroxy acids, a process that often occurs spontaneously even in aqueous solution. Diketene and β-propanolactone are made by the reaction of ketene with itself or with formaldehyde, respectively. Lactones with 7 to 24 atoms in the ring are prepared by slow distillation of the appropriate hydroxy acids under greatly reduced pressure.

Sesquiterpene lactones are a class of chemical compounds; they are sesquiterpenoids (built from three isoprene units) and contain a lactone ring, hence the name. They are found in many plants and can cause allergic reactions and toxicity if overdosed, particularly in grazing livestock.^[1]

Types

Structures of some sesquiterpene lactones:
A: Germacranolides, B: Heliangolides, C+D: Guaianolides, E: Pseudoguaianolides, F: Hypocretenolides, G: Eudesmanolides.

Sesquiterpene lactones can be divided into several main classes including germacranolides, heliangolides, guaianolides, pseudoguaianolides, hypocretenolides, and eudesmanolides.

Examples

Artemisinin, a new, highly-effective anti-malarial compound, is a sesquiterpene lactone found in Chinese wormwood. Lactucin, desoxylactucin, lactucopicrin, lactucin-15-oxalate, lactucopicrin-15-oxalate are some of the most prominent found in lettuce and spinach, giving most of the bitter taste to these crops.

One eudesmanolide, 3-oxo-5αH,8βH-eudesma-1,4(15),7(11)-trien-8,12-olide, can work with vernolic acid and other compounds in plants to reduce inflammation.^[2]

N-Acyl homoserine lactone

From Wikipedia, the free encyclopedia

General chemical structure of an N-acyl homoserine lactone

N-Acyl homoserine lactones (AHLs or N-AHLs) are a class of signaling molecules involved in bacterial quorum sensing. Quorum sensing is a method of communication between bacteria that enables the coordination of group-based behavior based on population density. They signal changes in gene expression, such as switching between the flagella gene and the gene for pili for the development of a biofilm.

Mechanism

Signaling molecules are produced within the cell and are released into the environment. The resulting concentration of signaling molecules in the environment is dependent upon population density. Once the population density has reached a particular threshold, gene expression can begin. This allows bacteria to coordinate group-based behavior. N-AHLs produced by different bacteria differ in the length of the R-group side-chain. Chain lengths vary from 4 to 18 carbon atoms and in the substitution of a carbonyl at the third carbon.  It has also been suggested that N-AHLs alter local surface tension enough to create Marangoni flows which facilitate swarming and colony motility.

Example

One example of the involvement of AHLs in quorum sensing is in the regulation of the bioluminescent protein luciferase in the luminescent bacteria Vibrio fischeri. Similar pathways occur in other luminescent bacteria. In Vibrio fischeri, AHL binds to the protein product of the LuxR gene and activates it. The C-terminal domain of activated LuxR relieves the repression exerted by H-NS nucleoid proteins that bind to the promoters of LuxR, LuxI and the LuxCDABEG operon, as well as to A-T-rich stretches within that operon and other genomic regions. The product of LuxI catalyses the synthesis of AHL. Thus, AHL acts as an autoinducer. Transcription of the LuxCDABEG operon results in luminescence due to the expression of LuxA and LuxB, which form a protein known as a luciferase and the expression of LuxC, D, E, and G, which are involved in the synthesis of the luciferase's substrate, tetradecanal. This is an important feature of quorum sensing, as it makes little sense for one cell to waste the energy producing light, as the resulting light will be so faint that it will be more or less undetectable. Instead, once the bacterial population has reached a specific size, only then does light production commence.

Edman degradation

Homoserine lactone is also a product of the proteolytic reaction of cyanogen bromide (CNBR) with a methionine residue in a protein. This reaction is important for chemical sequencing of proteins, as the Edman degradation process is unable to sequence more than 70 consecutive residues.

PROBLEM
Can we not in the synthesis of lactone using catalyst?
Lactone is a cyclic ester is a condensation product of the alcohol-OH and-COOH carboxylic acid in the same compound. Characteristic of the lactone ring that is a cover consisting of two or more who has the carbonyl carbon and oxygen atoms are adjacent. This condensation reaction can also be referred to as the esterification reaction.
Transesterification reaction is an equilibrium reaction, therefore the presence of a catalyst to accelerate the achievement of a state of equilibrium of the reaction. Meanwhile, to obtain a greater abundance of the product ester compound, one of the reagents used must be in excess amount. The catalyst used can be either strong acid or strong base.
so, if the problem can only be or not, I think it can, but the reaction is slower