 <unk> acid is present in several Hydnellum species . This compound , derived metabolically from the shikimic acid pathway , inhibits the enzyme prolyl endopeptidase , which is involved in deteriorating certain <unk> that are believed to contribute to memory and learning . Hydnellum caeruleum and H. concrescens have several para @-@ terphenyl derivatives named <unk> , some of which can inhibit the enzyme alpha @-@ glucosidase . The compounds <unk> A and B are <unk> found in H. suaveolens and H. <unk> . The chemicals responsible for the fragrant anise @-@ like aroma of H. suaveolens have been identified as coumarin and para @-@ <unk> . 
