William F. Reynolds

Total assignment of 13C and 1H spectra of three isomeric triterpenol derivatives by 2D NMR: an investigation of the potential utility of 1H chemical shifts in structural investigations of complex natural products

It is shown that a recently proposed indirect heteronuclear shift-correlated pulse sequence, XCORFE, can be used to unambiguously assign the 13C spectra of three isomeric (C30H50O) triterpenols: taraxasterol (1a), pseudo-taraxasterol (2) and lupeol (3). This sequence gives excellent resolution combined with sensitivity far in excess of that given by 13C-13C connectivity experiments. Direct heteronuclear shift-correlated spectra are used to totally assign 1H spectra for 1a, 2, 3 and taraxasteryl acetate (1b). 1H chemical shifts are mainly sensitive to local environment and often show values which are characteristic of a particular environment. Knowledge of 1H chemical shifts and splitting patterns also places useful constraints on assignment of 13C chemical shifts for 13C1Hn units. It is strongly recommended that natural products chemists routinely use 2D NMR to assign 1H chemical shifts of complex organic derivatives in order to build up a data bank of 1H spectral data.

Assignment of 1H and 13C spectra and investigation of hindered side‐chain rotation in lupeol derivatives

Complete 1H and 13C spectral assignments are reported for lupeol (1a) and two derivatives where the C‐30 methyl group is replaced by CH2OH (1b) and HC O (1c). Compound 1c shows conformationally dependent substituent effects on 1H chemical shifts. It also shows line broadening of some 13C signals at 25 °C, suggesting hindered rotation of the side‐chain group. This is confirmed by low‐temperature spectra which show splitting of broadened peaks into pairs in a ca 2 : 1 area ratio. The free energy of activation of hindered rotation is estimated as 13.5 kcal mol−1. By contrast, 1a shows no evidence of hindered rotation down to −40 °C although NOE data suggest the presence of two conformers. Spartan molecular mechanics calculations confirm the presence of two stable conformers for 1a and 1c but overestimate the rotational barrier in 1a. The additional barrier in 1c probably reflects loss of conjugative stabilization during rotation. Copyright

PRENYLATED BENZOPHENONE DERIVATIVES FROM CARIBBEAN CLUSIA SPECIES (GUTTIFERAE). PLUKENETIONES B-G AND XEROPHENONE A

Abstract Six new prenylated benzophenone derivatives plukenetiones B-G (2–7) have been isolated from the fruits of the Barbadian plant Clusia plukenetii. These structures were elucidated by the use of 2D NMR spectroscopic methods. The regiochemistry of xerophenone A from Clusia portlandiana has been revised.

Comparison of13C Resolution and Sensitivity of HSQC and HMQC Sequences and Application of HSQC-Based Sequences to the Total1H and13C Spectral Assignment of Clionasterol

It is demonstrated that HSQC gives considerably better 13C resolution and sensitivity than HMQC for CH2 groups of natural products, particularly when combined with linear prediction. Similarly, coupled HSQC spectra provide a useful method for the determination of 1H multiplet structure and consequent assignment of individual CH2 protons as axial or equatorial in fused cyclohexane rings. These and related techniques are used to assign 1H and 13C spectra of the marine sterol clionasterol.

Steroid hydroxylation by whetzelinia sclerotiorum, Phanerochaete chrysosporium and Mucor plumbeus

The fungi Whetzelinia sclerotiorum ATCC 18687, Phanerochaete chrysosporium ATCC 24725 and Mucor plumbeus ATCC 4740 were examined for their ability to perform steroid biotransformations under single phase, pulse feed conditions. The steroids 3beta-hydroxyandrost-5-en-17-one (dehydroepiandrosterone) (1), 17beta-hydroxyandrost-4-en-3-one (testosterone) (5), 3beta-hydroxypregn-5-en-20-one (pregnenolone) (3), pregn-4-ene-3,20-dione (progesterone) (9), 17alpha,21-dihydroxypregn-4-ene-3,11,20-trione (cortisone) (11), 17alpha,21-dihydroxypregna-1,4-diene-3,11,20-trione (prednisone) (14), and 3-hydroxyestra-1,3,5(10)-trien-17-one (estrone) (15) were fed to each fungus. The production of a number of novel metabolites is reported. Of the fungi investigated W. sclerotiorum performed the most interesting biotransformations and had a clear propensity for 2beta, 6beta/7beta and 15beta/16beta hydroxylations. P. chrysosporium was more prone functionalize steroids in the allylic position. Oxygen insertion at C-14 by M. plumbeus is reported for the first time. All three micro-organisms exhibited redox activity.

Investigation of the Advantages and Limitations of Forward Linear Prediction for Processing 2D Data Sets

Although the potential advantages of f1 forward linear prediction for the processing of multi‐dimensional NMR spectra are well established, this method is surprisingly little used for 2D spectra used for organic structure determination. A detailed investigation of the advantages and limitations of f1 forward linear prediction for this purpose is reported. This is a reliable technique which is particularly useful for 1H‐detected 13C–1H shift correlation spectra, allowing up to 16‐fold linear prediction of the 13C axis of HSQC spectra. In general, the use of linear prediction allows one to obtain comparable 2D spectra in one quarter of the time or double the sensitivity in a comparable time relative to similar spectra without linear prediction. The one exception is the absolute value COSY spectrum, where linear prediction beyond a factor of two gives poor results. Linear prediction is generally superior to zero filling as a time‐saving technique, although the difference between the two approaches disappears as the f1 data point resolution approaches the natural linewidth. By contrast, f2 forward linear prediction is not recommended.

Plukenetione A. An unusual adamantyl ketone from Clusia plukenetii (guttiferae)

Abstract The structure of plukenetione A from Clusia plukenetii Urban has been shown by spectroscopic methods to be 1-benzoyl-8,8-dimethyl-3,5-bis(3-methyl-2-butenyl)-6-(2-methylpropenyl)tricyclo[3.3.1.1 3,7 ]decane-2,4,9-trione.

GLABRESCOL. A UNIQUE SQUALENE-DERIVED PENTA-THF DIOL FROM SPATHELIA GLABRESCENS (RUTACEAE)

Abstract The structure of glabrcscol from Spathelia glabrescens Planch has been shown by spcctroscopic methods to be a meso form of 2,23-dihydroxy-2,6,10,15, 19,23-hexamethyl-3,7,11,15,19-penta(oxacyclopentyl)tetracosane.

A pulse sequence which provides rapid, routine 1H13C shift-correlated spectra

Abstract A pulse sequence is evaluated which gives heteronuclear shift-correlated 2D spectra with full 1H1H decoupling by using a fixed 1H evolution time, T, in combination with incrementally stepped 1H and 13C refocusing pulses. Due to the nature of the sequence, T is restricted to one of two possible values: 0.012 ± 0.002 s and 0.020 ± 0.002 s. Using either of these values, the sequence gives excellent sensitivity and adequate 1H resolution making it feasible to obtain very rapid, routine shift-correlated spectra, even with very limited amounts of sample.

Mephedrone, a new designer drug of abuse, produces acute hemodynamic effects in the rat.

Mephedrone (4-methylmethcathinone) is a new and popular drug of abuse widely available on the Internet and still legal in some parts of the world. Clinical reports are now emerging suggesting that the drug displays sympathomimetic toxicity on the cardiovascular system but no studies have yet explored its cardiovascular effects. Therefore we examined the effects of mephedrone on the cardiovascular system using a combination of in vitro electrophysiology and in vivo hemodynamic and echocardiographic measurements. Patch clamp studies revealed that mephedrone, up to 30 μM, had little effect on the major voltage-dependent ion channels of the heart or on action potentials recorded in guinea pig myocytes. Subcutaneous administration of mephedrone (3 and 15 mg/kg) to conscious telemetry-implanted rats produced dose-dependent increases in heart rate and blood pressure which persisted after pre-treatment with reserpine. Echocardiographic analysis demonstrated that intravenous injection of mephedrone (0.3 and 1mg/kg) increased cardiac function, including cardiac output, ejection fraction, and stroke volume, similar to methamphetamine (0.3mg/kg). We conclude that mephedrone is not directly pro-arrhythmic, but induces substantial increases in heart rate, blood pressure and cardiac contractility and this activity contributes to the cardiovascular toxicity in people who abuse the drug.