( ( Class ( of ( Compounds Retinoids ) ) ) ( ( are ( ( a class ) ( of ( compounds ( consisting ( of ( ( four ( isoprenoid units ) ) ( joined ( in ( a ( head-to-tail manner ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (NNP Class)) (PP (IN of) (NP (NNP Compounds) (NNPS Retinoids)))) (VP (VBP are) (NP (NP (DT a) (NN class)) (PP (IN of) (NP (NP (NNS compounds)) (VP (VBG consisting) (PP (IN of) (NP (NP (CD four) (JJ isoprenoid) (NNS units)) (VP (VBN joined) (PP (IN in) (NP (DT a) (JJ head-to-tail) (NN manner))))))))))) (. .)))
Class of Compounds Retinoids are a class of compounds consisting of four isoprenoid units joined in a head-to-tail manner.
(ROOT (S (NP (EX There)) (VP (VBP are) (NP (NP (CD four) (NNS classes)) (PP (IN of) (NP (JJ biochemical) (NNS compounds))))) (. .)))