Table 1

Mass spectrometry data for FK520 analogs

Compound	LC/MS^1-a		HRMS^1-b
Compound	[M ⁺ H]⁺	[M-H₂O ⁺H]⁺	[M-2H₂O ⁺H]⁺	Calculated	Observed
FK520	793	775	757
13-H FK520	763	745	727	C₄₂N₆₆NO₁₀
				([M-H₂O ⁺ H]⁺)
				744.4681	744.4630
13-Me FK520	777	759	741	C₄₃H₆₉NO₁₁Na
				([M ⁺ Na]⁺)
				798.4763	798.4786
13-H-15-H FK520	733	715	697	C₄₁H₆₅NO₁₀Na
				([M ⁺ Na]⁺)
				754.4501	754.4522
13-H-15-Me FK520	747	729	711	C₄₂H₆₇NO₁₀Na
				([M ⁺ Na]⁺)
				768.4657	768.4663
13-H-15-Et FK520	N.O.	743	725	C₄₃H₆₈NO₉
				([M-H₂O ⁺ H]⁺)
				742.4889	742.4897
13-Me-18-OH FK520	793	775	757	C₄₃H₇₀NO₁₂
				([M ⁺ H]⁺)
				792.4893	792.4919

N.O., not observed.
↵1-a Cultures were screened for FK520 analog production by online extraction LC/MS. Under the conditions used, FK520 analogs give prominent ions due to single and double dehydration ([M-H₂O + H]⁺ and [M-2H₂O + H]⁺) of the parent compounds and modest pseudomolecular ions ([M + H]⁺).
↵1-b High-resolution mass spectrometry.