2J,(3)J-HMBC: A new long-range heteronuclear shift correlation technique capable of differentiating (2)J(CH) from (3)J(CH) correlations to protonated carbons

The development of a series of new, accordion-optimized long-range heteronuclear shift correlation techniques has been reported. A further derivative of the constant time variable delay introduced in the IMPEACH-MBC experiment, a STAR (Selectively Tailored Accordion F(1) Refocusing) operator is described in the present report. Incorporation of the STAR operator with the capability of user-selected homonuclear modulation scaling as in the CIGAR-HMBC experiment, into a long-range heteronuclear shift correlation pulse sequence, (2)J,(3)J-HMBC, affords for the first time in a proton-detected experiment the means of unequivocally differentiating two-bond ((2)J(CH)) from three-bond ((3)J(CH)) long-range correlations to protonated carbons. Copyright 2000 Academic Press.

11-Isopropylcryptolepine: A novel alkaloid isolated from cryptolepis sanguinolenta characterized using submicro NMR techniques

A new alkaloid has been isolated from extracts of the West African plant Cryptolepis sanguinolenta and identified by submicro NMR techniques as 11-isopropylcryptolepine (1). The unusual incorporation of the isopropyl group at the 11-position of the indolo[3,2-b]quinoline nucleus is suggestive of a mixed biosynthetic origin for the alkaloid.

Thalprzewalskiinone, a new oxobenzylisoquinoline alkaloid from thalictrum przewalskii

A novel oxobenzylisoquinoline alkaloid, thalprzewalskiinone (1), was isolated from the roots of Thalictrum przewalskii, and its structure was established via spectroscopic analysis. Five other alkaloids were isolated: the protoberberines pseudocoptisine and berberine, the aporphines (+)-N-methylnantenine and (+)-magnoflorine, and the simple isoquinolone N-methyl-6,7-dimethoxyisoquinolone. Isovanillin was also isolated from this extract.

Low-level long-range 1H-15N heteronuclear shift correlation at natural abundance using submicro NMR techniques

Gradient inverse-detected NMR methods have provided experimental access to long-range 1H-15N heteronuclear shift correlation data at natural abundance. When used in conjunction with newly developed submicro-inverse-detection gradient (SMIDG) NMR probes, sample size requirements are dramatically reduced. Long-range 1H-15N GHMBC data are shown for a 1 mg sample ( approximately 3 &mgr;mol, 0.11 M) of the alkaloid strychnine (1) dissolved in 30 &mgr;L of CDCl3. All of the correlations observed in previous studies using samples in the range of 20-40 mg in 5 mm NMR probes were observed in data acquired overnight on a 1 mg sample in a 1.7 mm SMIDG NMR probe. A previously unreported long-range correlation, 3JH-15a-N(19), was observed in data recorded over a weekend for the 1 mg sample. Data recorded over a weekend using a 1 &mgr;mol (334 &mgr;g) sample of strychnine (1) in 30 &mgr;L of CDCl3 contained the majority of the responses from the 1 mg sample. The practical limit of detection for long-range 1H-15N heteronuclear shift correlation data at natural abundance would appear to be approximately 1 &mgr;mol with data acquisition over a weekend or longer using present submicro-NMR probe technology.