Abstract
Enzymes from Salvia officinalis and Tanacetum vulgare leaf epidermis catalyze the conversion of the acyclic precursor geranyl pyrophosphate to the cyclic monoterpenes (+)- and (-)-bornyl pyrophosphate, respectively. The antipodal cyclizations are considered to proceed by the initial isomerization of the substrate to the respective bound tertiary allylic intermediates (-)-(3R)- and (+)-(3S)-linalyl pyrophosphate. [(3R)-8,9-14C,(3RS)-1E-3H] Linalyl pyrophosphate (3H:14C = 5.22) was tested as a substrate with the cyclases from both sources to determine the configuration of the cyclizing intermediate. This substrate yielded (-)-bornyl pyrophosphate with 3H:14C ratio greater than 31, indicating specific utilization of (+)-(3S)-linalyl pyrophosphate as predicted. With the (+)-bornyl pyrophosphate cyclase, the 3H:14C ratio of the product was about 4.16, indicating a preference for the (-)-(3R)-enantiomer, but the ability also to utilize (+)-(3S)-linalyl pyrophosphate. (3R)- and (3S)-[1Z-3H]Linalyl pyrophosphate were separately compared to the achiral precursors [1-3H] geranyl pyrophosphate and [1-3H]neryl pyrophosphate (cis-isomer) as substrates for the cyclizations. All functional precursors afforded optically pure (-)-(1S,4S)-bornyl pyrophosphate with the T. vulgare-derived cyclase (as determined by chromatographic separation of diastereomeric ketals of the derived ketone camphor), and (+)-(3S)-linalyl pyrophosphate was the preferred substrate. With the (+)-bornyl pyrophosphate cyclase from S. officinalis, geranyl, neryl, and (-)-(3R)-linalyl pyrophosphates gave the expected (+)-(1R,4R)-stereoisomer as the sole product, and (-)-(3R)-linalyl pyrophosphate was the preferred substrate. However, (3S)-linalyl pyrophosphate yielded (-)-(1S,4S)-bornyl pyrophosphate, albeit at lower rates, indicating the ability of this enzyme to catalyze the anomalous enantiomeric cyclization.
Highlights
Enzymes from Salvia officinalis and Tanacetumvul- nyl pyrophosphate and to (-)-(lS,4S)-bornyl pyrophosphate gare leaf epidermiscatalyze the conversion of the have been isolated from sage (Saluia officinalis) and from acyclic precursor geranyl pyrophosphate to the cyclic tansy (Tameturn uulgare), respectively, and have been parmonoterpenes (+)- and (-)-bornyl pyrophosphate, re- tially purified and characterized [1, 2]
5.22) was tested as a substrate with the cyclases from both sources to determine the configuration of the cyclizing intermediate. This substrateyielded (-)-bornyl pyrophosphate with 'H:14C ratio >31, indicating speare unique, far, among monoterpene cyclasesin affording a pyrophosphate ester as the initial cyclic product, a feature which has allowed direct examination of the role of the pyrophosphate moiety in thecyclization process [4, 5]
(3R)-and (3S)-[1Z-SH]Linalyl pyrophosphate were must be capable of transforming the substrate to a bound separately compared to the achiral precursors [l-'H] intermediate competent to cyclize and of catalyzing the cycligeranyl pyrophosphateand [l-'H]neryl pyrophosphate zation reaction itself
Summary
ENANTIOSELECTIVITY INTHE ENZYMATIC CYCLIZATION OF (+)- AND (-)-LINALYL PYROPHOSPHATE TO (+)- AND (-)-BORNYL PYROPHOSPHATE*. 5.22) was tested as a substrate with the cyclases from both sources to determine the configuration of the cyclizing intermediate This substrateyielded (-)-bornyl pyrophosphate with 'H:14C ratio >31, indicating speare unique, far, among monoterpene cyclasesin affording a pyrophosphate ester as the initial cyclic product, a feature which has allowed direct examination of the role of the pyrophosphate moiety in thecyclization process [4, 5]. With the (+)-bony pyrophosphate cyclase from S. officinalis, geranyl, neryl, and (-)-(3R)-linalyl pyrophosphates gavethe expected (+)-(1R,4R)-stereoisomer as the sole product, and (-)-(3R)-linalyl pyrophosphatewasthe preferred substrate This general proposal is consistent with the results of numerous model studies of terpenoid cyclizations [12,13,14,15,16] and with biosynthetic investigations relevant to the isomerization of geranyl pyrophosphate to linalyl pyrophosphate [10, 17, 18].
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