Cyclic esters derived by multiple esterification between two (usually) or more molecules of lactic acid or other hydroxy carboxylic acids.
They are designated as dilactides, trilactides, etc. according to the number of hydroxy acid residues, e.g. a dilactide (a 1,4-dioxane-2,5-dione):
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Source:
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1346 (https://doi.org/10.1351/pac199567081307)